Environmental Health & Safety

Laser Safety Program

January 2011


In accordance with your Environmental Health & Safety Policy, the Massachusetts Department of Public Health, the Occupational Safety and Health Administration (OSHA) and other local, state and federal requirements, including American National Standards Institute, ANSI Z-136.1-2000 Amherst College has designed the following Laser Safety Standard Operating Guidelines for the health and safety of the faculty, staff, students, contractors, and visitors.




To provide the faculty, staff, students, contractors and visitors of Amherst College with the requirements and safe operating practices for low, medium, and high powered lasers in the classrooms, laboratories, construction sites and other locations where Class II, III, and IV lasers are placed, operated, maintained, or stored.


Under the direction of the Radiation Use Committee, The Laser Safety Officer, The Chemical Hygiene Officer, Environmental Health and Safety and qualified faculty, the placement, operation, maintenance and storage of Class II, III, and IV lasers shall be conducted in a manner, identified here-in that will ensure personnel protection for authorized and affected faculty, staff, students, contractors, and visitors at Amherst College. The College is committed to limit exposure to laser radiation as specified in the Massachusetts General Law Chapter 111, section 51. Additionally, the College will require adherence to the applicable sections of ANSI Z 136.1-2000, National Standard for Safe Use of Lasers, the Laser Institute of American Guidelines, and Prudent Practices in the Laboratory to ensure that health and safety of the campus community, and to preserve and protect College property and the environment.


The definitions below are specific to the Amherst College Laser Safety Standard Operating Guidelines and may not be all inclusive. Some terms such as laser classes will be defined, when appropriate, in the specific sections of the guidelines.

Absorption - Transformation of radiant energy to a different form of energy by interaction with matter.

Accessible Emission Limit (AEL) - Maximum accessible emission level within a particular class.

Accessible Optical Radiation (AOR) - Optical radiation to which the human eye or skin may be exposed for the condition (maintenance, operation, or service) specified.

Alpha Max - The angular limit beyond which extended source Maximum Permissible Exposures (MPE's) for a given exposure duration are expressed as a constant radiance or integrated radiance.

  • The value is defined as 100 mrad.

Alpha Min - The apparent visual angle which decided small source viewing.

  • The value is defined as 1.5 mad.

Aperture - An opening or window through which radiation passes.

Aphakic - An eye condition in which the crystalline lens is not present.

Apparent Visual Angle - The Angular substance of source as calculated from the source size and distance from the eye. It is not the beam divergence of the source.

Attenuation - Decrease in the radiant flux as it passes through an absorbing or scattering medium.

Authorized Personnel - Individuals who, because of education and training (including safety), and having been approved of by the Amherst College Laser Safety Officer, can install, operate, maintain and place laser equipment in rooms, laboratories or sites designed and setup for the intended purpose.

Authorized Operators shall, under the direction of the Laser Safety Officer:

  1. Be able to exercise good judgment when using the laser or laser systems.
  2. Have the level of training and experience of laser users commensurate with the type of work and level of hazard.
  3. Be aware of potentially hazardous radiation that may be present and that appropriate safety precautions that will be required.
  4. Be familiar with the laser being used, Manufacturers Specifications and the Safety Protocols required.
  5. Be familiar with the other hazards in the laboratory that are unrelated to the laser, but have a potential to cause illness, injury or property damage.

Aversion Response - Closure of the eyelid, or movement of the head to avoid an exposure to a noxious stimulant or bright light. The aversion response to an exposure from a bright laser source is assumed to occur within 0.25s, including the blink reflex time.

Beam - A collection of rays characterized by direction diameter (or dimensions) and divergence (or convergence).

Beam Diameter - Distance between diametrically opposed points in the cross-section of a beam where the power per unit area is 1/e (0.368) times that of the peak power per unit area.

Beam Divergence - The plane angle projection of the cone that includes 1-1/e (ex. 63.2%) of the total radiant energy or power.

  • The value of the distance is expressed in radians or milliradians.

Correction Factors

  1. CA - Correction factor that increases the maximum permissible exposure values in near infrared (IRA) spectral band (700-1400nm) based upon reduced absorption properties of melanin pigment granules found in the skin and in the retinal pigment epithelium.

  2. CB - Correction factor that increases the maximum permissible exposure values in the red end of the visible spectrum (450-600nm), because of greatly reduced photochemical hazards.

  3. CC - Correction factor that increases the maximum permissible exposure values for ocular exposure because of pre-retinal absorption of radiant energy in the spectral region between 1150 and 1400 nm.

  4. CE - Correction factor used for calculating the extended source Maximum Permissible Exposure, when the laser source subtends a visual angle exceeding alpha min.

  5. CP - Correction factor which the maximum permissible exposure for repetitive-pulse exposure of the eye.

Carcinogen - An agent potentially capable of causing cancer.

Coagulation - The process of congealing by an increase in viscosity characterized by a condensation of material from a liquid to a gelatinous or solid state.

Coherent - A light beam is said to be coherent when the electric vector at any point in it is related to that at any other point by a definite, continuous function.

Collateral Radiation - Any electromagnet radiation except laser radiation, emitted by a laser or a laser system which is physically necessary for its operation.

Collecting Optics - Lenses or optical instruments having magnification and thereby producing an increase in energy or power density. Such devices may include telescopes, binoculars, microscopes, or loops.

Collimated Beam - Essentially a "parallel" a beam of light with very low divergence or convergence.

Conjunctival Discharge - Increased secretion of mucous from the eye.

Continuous Wave (CW) - The output of a laser which is operated in a continuous rather than a pulsed mode. In this standard, a laser operating with a continuous output for a period > 0.25s is regarded as a CW laser.

Controlled Area - An area where the activity of those within, or other affected persons are subject to control and supervision for the purpose of protection from radiation hazards.

Cornea - Transparent outer coating of the eye which covers the iris and the crystalline lens. It is the main refracting element of the eye.

Critical Frequency (CF) - The pulse repetition frequency above which the laser output is considered continuous wave (CW).

  • For a 10s exposure to a small source, the CF is 55kHz for wavelengths between 0.4 and 1.05 micrometers and 20kHz for wavelengths between 1.05 and 1.4 micrometers.

Diffuse Reflection - Change of the spatial distribution of a beam of radiation when it is reflected in many directions by a surface of by a medium.

Diopter - A measure of the power of a lens, defined as 1/fo, where fo is the focal length of the lens to meters.

Divergence - The plane angle projection of the cone that includes 1-1/e (i.e. 63.2%) of the total radiant energy or power.

  • The value of the divergence is expressed in radians or milliradians.
  • Many lasers have astigmatic divergence. There are different divergences in 2 axes. In such conditions, the divergences may be considered separately or averaged.

Effective Energy - (Queff) Energy, in joules, through the applicable measurement aperture.

Effective Power - Power in watts, through the applicable measurement aperture.

Electromagnetic Radiation - The flow of energy consisting of orthogonally vibrating electric and magnetic fields lying transverse to the direction of propagation.

  • X-ray, ultraviolet, visible, infrared and radio waves occupy various portions of the electromagnetic spectrum and differ only in frequency, wavelength, and photon energy.

Embedded Laser - An enclosed laser with an assigned lass number higher than the inherent capability of the laser system in which it is incorporated, where the system's lower classification is appropriate due to the engineering features limiting accessible emission.

Energy - The capacity for doing work. Energy content is commonly used to characterize the output from pulsed lasers, and is generally expressed in joules.

Erythema - Redness of skin due to congestion of the capillaries.

Fail-Safe Interlock - An interlock where the failure of a single mechanical or electrical component of the interlock will cause the system to go into, or remain in, a safe mode.

  • Interlocks shall be included in the housing of the laser and the access points to the "controlled area".

Focal Length - The distance, measured in centimeters, from the secondary nodal point of a lens to the secondary focal point.

  • For a thin lens imaging a distant source, the focal length is the distance between the lens and the focal point.

Focal Point - The point toward which radiation converges or from which radiation diverges or appears to diverge.

Half Power Point - The value on either the leading or trailing edge of a laser pulse at which the power is ½ of its maximum value.

Hertz (Hz) - The unit which expresses the frequency of a periodic oscillation in cycles per second.

Infrared (IR) - The region of the electromagnetic spectrum between the long-wavelength extreme of the visible spectrum (about 0.7 micrometers) and the shortest microwaves (about 1mm).

Integrated Radiance - The integral of the radiance over the exposure duration, expressed in joules-per-square-centimeter per-steradian.

Intrabeam Viewing - The viewing condition where by the eye is exposed to all or part of a laser beam.

Irradiance - Radiant power incident per unit area upon a surface, expressed in watts-per-square-centimeter.

  • Also known as Power Density.

Joule - A unit of energy. 1 joule = 1 watt per second.

Lambertian Surface - An ideal surface whose emitted or reflected radiance is independent of the viewing angle.

Laser - A device that produces radiant energy predominately by stimulated emission. Laser radiation may be highly coherent temporally, or spatially, or both.






        Laser Barrier - A device used to block or attenuate incident direct or diffuse laser radiation.

        • Laser barriers are frequently used during times of service to the laser system when it is desirable to establish a boundary for a temporary or permanent laser controlled area

        Laser Diode - Laser employing a forward -biased semiconductor junction as the medium.

        Laser Pointer - A Class II or III a laser product that emits a low-divergence visible beam of less than 5mW and is intended for designating specific objects or images during discussions, lectures or presentations as well as for the aiming of beams for construction sites for the purpose of leveling etc.

        Laser Safety Officer (LSO) - The person designated by the Amherst College Radiation Safety Committee, who has the authority to train, authorize, control and enforce proper laser safety work practices, and con effect the knowledgeable evaluation and control of laser hazards.

        Limiting Aperture (Df) - The maximum diameter of a circle over which radiance and radiant exposure are averaged for purposes of hazard evaluation and classification.

        Limiting Cone Angle - Angle of acceptance for measurement of photochemical hazard for extended sources with radiance and integrated radiance.

        Maintenance - Performance of those adjustments or procedures specified here-in, which are to be performed by the authorized user to ensure the intended performance of the product. It does not include operation or service.

        Maximum Permissible Exposure (MPE) - The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin.

        May - To be allowed or permitted to.

        Nominal Hazard Zone (NHZ) - The area within which the level of direct, reflected, or scattered radiation during normal operation can exceed the Maximum Permissible Exposure.

        Nominal Ocular Hazard Distance (NOHD) - The distance along the axis of the unobstructed beam from a laser, fiber end, or connector to the human eye beyond which the irradiance or radiant exposure, during installation or service, is not expected to exceed the appropriate maximum permissible exposure.

        Operation - The laser or laser system working over the full range of its intended functions.

        Optically Aided Viewing - Viewing of the laser source with an optical device such as a hand magnifier, microscope, binoculars, telescope or eye loupe.

        • Optically aided viewing does not include viewing with corrective eyewear or with indirect image concreters.

        Optical Density - Logarithm to the base ten of the reciprocal of the transmittance.

        •  The greater the optical density, the lower the transmittance. Ten times the optical density is equal to the transmission loss expressed in dB's.
          • An optical density of 0.3 corresponds to a transmission loss of 3 dB, i.e., 50%

        Plasma Radiation - Black-body radiation by luminescence of matter in a laser generated plume.

        Power - The rate at which energy is emitted, transferred, or received.

        • Unit : watts (joules per second)

        Protection Housing - The enclosure surrounding the laser or laser system that prevents access to laser radiation above the MPE level. The protective housing may enclose associated optics and workstation, and limits access to other associated radiant energy emissions and to electrical hazards associated with components and terminals.

        Pulse Duration - The duration of a laser pulse, usually measures the time interval between the ½ power points on the leading and trailing edges of the pulse.

        Pulse Repetition Frequency (PRF) - The number of pulses occurring per second, expressed in hertz.

        Pulsed Laser - A laser which delivers its energy in the form of a single pulse or a train of pulses.

        Q-Switch - A laser for producing very short (~10-250 nanoseconds) intense laser pulses by enhancing the storage and dumping or electronic energy in and out of the lasing medium, respectively.

        Q-Switched Laser - A laser that emits short (~10-250 nanoseconds) high power pulses by means of a Q-switch.

        Radian (rad) - A unit of angular measure equal to the angle subtended at the center of a circle by an arc whose length is equal to the radius of the circle.

        • 1 radian ~ 57.3 degrees

        Radiance - Radiant flux or power output per unit solid angle per unit area expressed in watts-per-centimeter squared-per-steradian.

        Radiant Energy - Energy emitted, transmitted, or received in the form of radiation.

        • Unit : Joules

        Radiant Exposure - Surface density of the radiant energy received, expressed in joules-per-centimeter squared.

        Radiant Flux - Power emitted, transferred, or received in the form of radiation.

        • Unit : Watts
        • Also known as Radiant Power

        Radiant Intensity - Quotient of the radiant flux leaving a source and propagated into an element of a solid angle containing the direction, by the element of solid angle.

        Radiant Power - Power emitted, transferred, or received in the form of radiation.

        • Unit : Watts
        • Also known as Radiant Flux

        Reflectance - The ratio of total reflected radiant power to total incident power.

        • Reflectivity

        Reflection - Deviation of radiation following incidence on a surface.

        Refraction - The bending of a beam of light in transmission through an interface between two (2) dissimilar media or in a medium whose refractive index is a continuous function of position.

        Repetitive Pulse Laser - A laser with multiple pulses of radiant energy occurring in sequence.

        Scanning Laser - A laser having a time-varying direction, origin, or pattern of propagation with respect to a stationary frame of reference.

        Shall - A directive or requirement.

        Should - Used to express probability or expectation, a recommended practice.

        Service Performance of those procedures or adjustments described by the manufacturer's service instructions which may affect any aspect of the performance of the laser or laser system.

        • Service does not include maintenance or operation.

        Solid Angle - 3 dimensional angular spread at the vertex of a core measured by the area intercepted by the cone on a unit sphere whose center is the vertex of the cone.

        Ultraviolet Radiation - Electromagnetic radiation which can be detected by the human eye.

        • Range = 0.18 - 0.4 micrometers.

        Visible Radiation - (light) electromagnetic radiation which can be detected by the human eye.

        • Range = 0.4 - 0.7 micrometers

        Watt Unit of Power or Radiant Flux

        • 1 watt = 1 Joule per second

        Wavelength the distance between two (2) successive points on a periodic wave which have the same phase.

        Laser Safety Officer

        The Amherst College Laser Safety Officer has the authority and responsibility to implement, review and enforce the control of lasers and laser systems, to evaluate and mitigate any identified laser hazards in accordance with the applicable regulations and appropriate standards, under the direction of the Radiation Use Committee.

        The Laser Safety Officer shall review and modify Amherst College Laser Safety Standard Operating Guidelines, establish Nominal Hazards Zones, identify engineering controls, personal protective equipment, and conduct environmental inspections and training in cooperation with Environmental Health & Safety and the Chemical Hygiene Officer. The Laser Safety Officer can delegate appropriate responsibilities to the Radiation Safety Committee, Environmental Health & Safety, the Chemical Hygiene Officer, and other authorized Amherst College faculty, staff and students.

        Laser Safety Officers duties shall include, but not be limited to:

        1. Classification of laser or laser systems unless classified by the laser specific manufacturer.

        2. Hazard evaluations of laser work areas, including NHZ.

        3. Insuring the use of proper administrative and procedural control measures for reasons of health, safety and the preservation of property.

        4. Assist with the design, approval and implementation of administrative and procedural guidelines, including:

        • Alignment procedures
        • Personal Protective Equipment
        • Laser signage and lights
        • Maintenance repair and service
        • Operations and use
        • Qualifications of laser and laser system operators
        • Housekeeping and general laboratory safety

        5. Set up and operation of new or renovated laser facilities in classes III and IV.

        6. Insure proper training and testing for potential laser operators.

        7. Advise, when necessary the Radiation Safety Committee on matters pertaining to laser and laser systems of Class III and IV

        8. Periodically review with the department of Human Resources the status of employees and students records, specifically related to general medical and eye, as it pertains to laser use.

        9. Periodically inspect and mitigate hazardous conditions in the laser facilities to reduce the risk of illness, injury or property damage

        10. Insure the necessary records are being kept and maintained in accordance with local, state and federal regulations.

        11. Assist the office of Environmental Health and Safety with inspection and accident/incident investigations to improve the health and safety of laser facilities.

        Hazard Classification

        Laser Classifications are based on the potential for personnel injury and property damage. Both the laser and laser systems can be considered hazardous from an exposure to excessive radiation, during operation.

        Lasers, because they produce a photon beam through stimulated emission utilizing photons of the same wavelength and in phase (coherence), traveling in the same direction are considered hazardous and require warning labels, even if less then 1mW. The laser generates radiant energy in the optical portion of the electromagnetic spectrum with wavelengths between 180nm and 1mm.

        Although the wattage of a 1 mW laser is considerably less than either a flahslight or a multicolored 100 W light bulb, it is still hazardous. It is hazardous because of the highly concentrated, point-directed beam.

        When a concentrated "point source" laser beam makes contact with skin, it can raise the temperature of the tissue several degrees. Photochemical changes can also occur because of the potential high concentration of photons. For the eyes, the lens and cornea concentrate laser energy by 100,000 times so that retinal burn or lesion is possible.

        Lasers with wavelengths between 400 and 1400nm are the most hazardous because they can cause eye injury. Laser operators and other affected persons exposed to a continuous stream of pulses from a repetitively pulsed laser, are at more risk than if they were exposed to a single pulse of the same pulse energy or exposure to a continuous wave source with the same average power.

        Only authorized Amherst College faculty staff, students, qualified representatives and service technicians, who are approved by the Laser Manufacturer shall be permitted to operate, service or otherwise handle lasers that are regulated by the Standard Operating Procedure.

        Laser - Common Hazards

        The four categories of basic laser hazards are:

        Laser Radiation

        1. Infrared
        2. Ultraviolet
        3. Visible
        4. X-rays
        5. Gamma rays
        Laser beams emit optical radiation
        •  Non-ionizing radiation can be:
          • Ionizing radiation, which have been known to cause biological abnormalities are:
        • Eye Hazards
        1. Burns of the cornea and/or retina are possible from acute exposure, depending on the wavelength.
        2. Corneal or lenticular opacities (cataracts) and/or retinal injury may be possible if the eyes are exposed to excessive levels otherwise known as chronic exposure
        • Skin Hazards

          Burns are a concern from an acute exposure to high levels of optical radiation.

          • At certain ultraviolet wavelengths, skin cancer could present itself.
          • Sunburn that cause skin cancer and accelerated aging of skin can occur at 230-280nm wavelength range. Exposure to ultraviolet radiation in the 280-315 range (UV-B) is extremely hazardous.
          • Photosensitive reactions occurs in the 310-400nm range (near UV) and 400-600nm range (visible) wavelength regions.
        • Chemical Hazards
        Some lasers such as chemical dye and excimer lasers could be hazardous from an absorption and/or inhalation exposure.
        • Electrical Hazards
        Electrical hazards are always present, especially high-power laser systems.
        • Additional Hazards
        1. Administrative and procedural non-compliance
        2. Cryogenic and other coolant hazards
        3. Fires and Explosions
        4. Noise exposure
        5. Radiation from uncontrolled high voltage (>15KV) power supply units

        Class II and IIIa lasers that are used on sites, such as construction for the purpose of aligning, leveling etc shall be operated by personnel that are trained and qualified by the manufacturer or manufactures representative.

        Classifications of lasers are based on the maximum out put available for the intended use. The most hazardous possible operation for a specific laser or laser system shall dictate the actual classification level.

        1. Multi-wavelength Lasers can operate as a single or multiple wavelength region. Classification is based on the most significant potential hazard for that particular laser.
        2. Repetitive Pulse Lasers must be evaluated using certain correction factors as it may pertain to eye and skin exposure.
        In order to properly classify all lasers, the following must be identified:
        1. Wavelength or wavelength range
        2. Average power output, within specified limiting apertures and limiting exposure duration for both Continuous Wave (CW) and Repetitive-Pulse lasers.
        3. For Pulsed Lasers:
        4. For extended source laser and laser systems like laser rays, injection laser diodes and lasers with permanent diffusers within the output optics will require, in addition to the other requirements identified here-in familiarity with the apparent visual angle enclosed by the source.
        5. For highly diverging beam lasers classification requires determination of effective power of energy at a specified distance.
          • It is identified from the closest ocular exposure distance, but is not less than 10 cm.
          • If determination of hazards is being made from optically aided viewing equipment such as telescopes or binoculars, it should be made at the closest viewing distance, but not closer then 2 meters, for all wavelengths that transmit through common optics.

        Reflected Energy

        When a laser beam strikes a matte surface a diffuse reflection is produced and it is considered an extended source when viewed at a close distance. Laser energy from a diffuse reflection is less hazardous than that from a direct beam. Authorized operators should note that some lasers can pose a serious hazard for any person observing a diffuse surface, such as walls, shields, curtains, mattes and target boards, used as a "stop" for a laser beam. Diode projection systems have a larger source than the more common laser systems. The MPE's for the extended sources are elevated because the laser energy or power entering the eye is distributed over a wider surface of the retina, which lowers the potential for retinal heating.

        To be safe, the hazard evaluation should consider all laser sources to be small sources

        Class I Lasers and Laser Systems

        Class I Lasers or Laser Systems contain a laser that is not able to emit accessible laser radiation levels in excess of the applicable Class I AEL for any emission duration during operation as specified by the manufacture.

        1. Class I Lasers meeting the above criteria are exempt form all control measures or other forms of surveillance with the exception of applicable requirements for embedded lasers.
        2. The maximum exposure duration should not be greater than 30,000s,
            • 100s shall be used
            • the exception applies strictly to emitted laser radiation hazards and not to other potential hazards.
        3. Class I Lasers can also be identified by the Amherst College Laser Safety Officer on the basis of use for a limiting exposure duration of Tmax, less than 100s, provided that the accessible laser radiation does not exceed the corresponding Class I AEL for any emission duration within the maximum duration inherent in that specific use.
        • Laser Printer

        Class II Lasers and Laser Systems

        Class II Lasers and Laser Systems are visible (0.4 to 0.7 micrometers). Continuous Wave and Repetitive Pulse Lasers and Laser Systems which can emit accessible radiant energy exceeding the applicable Class I Accessible Emission Limit for the maximum duration inherent in the design or intended use of the laser or laser system, for any applicable pulse (emission) duration <0.25s and not exceeding an average radiant power of 1mW.

        1. Bar Code Scanners
        2. Laser Pointers
        3. Bar Code Scanners

        Class IIa Lasers: (very low power) Class II Lasers: (low power with visible beams)

        Class III Lasers and Laser Systems

        Class IIIa Lasers and Laser Systems that have accessible output between 1 and 5 times the Class I Accessible Emission Limit for wavelengths shorter than 0.4 micrometers or longer than 0.7 micrometers, or less than 5 times the Class II accessible emission limit for wavelengths between 0.4 and 0.7 micrometers.

        1. 2 types of class IIIa lasers based on irradiance:
          • Low irradiance produce a CW beam
            • Construction laser
            • Less than 2.5 mW/cm2
            • Momentary viewing is considered safe, unless viewed through an optical instrument for even a brief time.
        2. High irradiance class IIIa lasers have a small diameter beam.
        • greater than 2.5 mW/cm2
        • Momentary viewing is of this beam is not safe

        Class IIIb Lasers and Laser Systems are both Ultraviolet (UV) from 0.18 to 0.4 micrometers and Infrared (IR) form 1.4 micrometers to 1 millimeters that can emit accessible radiant power in excess of the Class IIIa accessible emission limit during any emission duration within the maximum duration inherent in the design of the laser and laser system, but which:

        1. Cannot emit an average radiant power in excess of 0.5W for >0.25s, and
        2. Cannot produce a radiant energy greater than 0.03 joules per pulse
        • Laser Pointer
        • Laser Scanners
        • Construction Alignment Devices
        • Entertainment Light Shows
        • Spectrometry
        • Stero-lithography

        Class IV Lasers and Laser Systems

        Class IV Lasers and Laser Systems are those units that emit radiation that exceed the accessible emission limit of a Class IIIb

        Lasers that are used for:

        • Research
        • Drilling
        • Cutting
        • Welding
        • Surgery

        Class IV Lasers

        Class IV Laser Safety

        Whenever possible the authorized laser operator shall use remote firing and video monitoring or remote viewing through a laser safety shield.

        Beam shutter and laser output filters should be used to reduce the laser beam irradiance to a less hazardous level, if the full beam power is not required.

        Lasers for Alignment, Leveling, and Surveying - Construction

        1. Whenever possible Class II lasers and laser systems should be used for construction activities such as alignment, leveling and surveying.
          • Although some applications require high ambient illumination levels with output powers of approximately 2mW, the output power for this type of laser cannot exceed 5mW.
        2. Only authorized (qualified and trained) personnel shall be permitted to adjust, operate and place lasers used for construction purposes.
          • qualified laser operations shall be able to show proof of training, and shall have in their possession a card of certificate indicating same.
          • Certificates shall be obtained, and the laser operator has a thorough understanding of the equipment operation, maintenance and use.
        3. When lasers are not in use for extended periods of time, such as lunch breaks, overnight and at changes of shift, the beam shutters or caps shall be used, or the laser turned off or otherwise disconnected.
        4. When guiding the alignment of the laser, mechanical or electro-optic means shall be used as a detector, whenever possible.
        5. It is the responsibility of the authorized laser operator to take all of the appropriate precautions to assure that employees or affected persons do not look into the beam of the laser.
        6. The beam form the laser should be terminated at the end of its necessary path and shall in every application be terminated if the beam path extends beyond the controlled area of the construction site.
        7. The laser and laser system shall bear all of the appropriate labels, signs and stickers to indicate maximum output and the NHZ beyond which the laser beam irradiance does not exceed 2.5mW/cm².
        8. At no time shall unauthorized personnel handle or gain access to the laser or laser system indicated in this section. The units shall be locked or otherwise secured to prevent improper use.
        9. At no point should the laser beam be placed at or near eye level.
        10. Accidental illness or injury caused by improper maintenance, operation use or storage of the laser or laser system, which has been determined to have been used contrary to manufacturers specifications or training is the responsibility of the authorized person to whom the laser or laser system was assigned.
        11. The laser beam must not be pointed at mirror-like (specular) surfaces.
        12. The authorized laser operator shall, under the direction of the general contractors project manager post appropriate signage (Warning or Danger) on the doors of the building and the specific area in which the laser or laser system was being operated.
        13. Amherst College Physical Plant personnel using similar Class IIa, II and IIIa lasers shall be responsible for posting the required signage as indicated above.

        Laser Accidents and Incidents

        Most incidents involving lasers, laser beams, and laser systems adversely affect the eyes and skins. The types of situations that most frequently cause these conditions:
        1. Exposure to the beam during alignment
          • Improperly directed beams
          • Improper engineering controls
          • Misaligned optics
        2. Personal protective equipment issues
          • Eye protection - improper
          • Eye protection - not worn
        3. Other adverse conditions might include
          • Electrical hazards
          • Fires
          • Equipment malfunctions
          • Equipment use - improper
          • Inhalation of air containments, gases, or particles
          • Untrained, unauthorized personnel using equipment
          • Failure to follow standard operating guidelines
        • 75% of all laser incidents in laboratories occur during beam alignment.

        Laser Components

        A generalized laser consists of a lasing medium, a "pumping" system, and an optical cavity. The laser material must have a metastable state in which the atoms or molecules can be trapped after receiving energy from the pumping system. Each of these laser components is discussed below.

        Pumping Systems

        1. The pumping system imparts energy to the atoms or molecules of the lasing medium enabling them to be raised to an excited "metastable state" creating a population inversion. Optical pumping uses photons provided by a source such as a Xenon gas flash lamp or another laser to transfer energy to the lasing material. The optical source must provide photons which correspond to the allowed transition levels of the lasing material.
        2. Collision pumping relies on the transfer of energy to the lasing material by collision with the atoms (or molecules) of the lasing material. Again, energies which correspond to the allowed transitions must be provided. This is often done by electrical discharge in a pure gas or gas mixture in a tube.
        3. Chemical pumping systems use the binding energy released in chemical reactions to state.

        Optical Cavity

        If, on the other hand, one of the decaying atoms or molecules releases a photon parallel to the axis of the lasing material, it can trigger the emission of another photon and both will be reflected by the mirror on the end of the lasing rod or tube. The reflected photons then pass back through the material triggering further emissions along exactly the same path which are reflected by the mirrors on the ends of the lasing material. As this amplification process continues, a portion of the radiation will always escape through the partially reflecting mirror. When the amount of amplification or gain through this process exceeds the losses in the cavity, laser oscillation is said to occur. In this way, a narrow concentrated beam of coherent light is formed.

        The mirrors on the laser optical cavity must be precisely aligned for light beams parallel to the axis. The optical cavity itself, i.e. the lasing material, must not be a strong absorber of the light energy.

        Laser Media

        SOLID STATE LASERS employ a lasing material distributed in a solid matrix. One example is the Neodymium: YAG laser (Nd: YAG). The term YAG is an abbreviation for the crystal Yttrium Aluminum Garnet which serves as the host for the Neodymium ions. This laser emits an infrared beam at the wavelength of 1.064μ (μ = 10 -6 m). Accessory devices that may be internal or external to the cavity may be used to convert the output to visible or ultraviolet wavelength.

        GAS LASERS use a gas or a mixture of gases within a tube. The most common gas laser uses a mixture of helium and neon (HeNe), with a primary output of 632.8 nm (nm = 10 -9m) which is a visible red color. It was first developed in 1961 and has proved the forerunner of a whole family of gas lasers. All gas lasers are quite similar in construction and behavior. For example, the carbon dioxide (CO 2) gas laser radiates at 10μ in the far-infrared spectrum. Argon and krypton gas lasers operate with multiple frequency emissions principally in the visible spectra. The main emission wavelengths of an argon laser are 488 and 514 nm.

        DYE LASERS use a laser medium that is usually a complex organic dye in liquid solution or suspension. The most striking feature of these lasers is their "tunability."

        • Proper choice of the dye and its concentration allows the production of laser light over a broad range of wavelengths in or near the visible spectrum.
        • Dye lasers commonly employ optical pumping, although some types have used chemical reaction pumping. The most commonly used dye is Rhodamine 6G, which provides tunability over 200 nm bandwidth in the red portion (620 nm) of the spectrum.

        SEMICONDUCTOR LASERS (sometimes referred to as diode lasers) are not to be confused with solid state lasers. Semiconductor devices consist of two layers of semiconductor material sandwiched together. These lasers are generally very small physically and individually of only modest power. However, they may be built into larger arrays. The most common diode laser is the Gallium Arsenide laser with a central emission of 840 nm.

        Time Modes of Operation

        • CONTINUOUS WAVE (CW) lasers operate with a stable average beam power. In most higher power systems, one is able to adjust the power. In low power gas lasers, such as HeNe, the power level is fixed by design and performance and usually degrades with long term use.
        • SINGLE PULSED (normal mode) lasers generally have pulse durations of a few hundred milliseconds. This mode of operation is sometimes referred to as long pulse or normal mode.
        • SINGLE PULSED Q-SWITCHED lasers are the result of an intracavity delay (Q-switch cell) which allows the laser media to store a maximum of potential energy. Then, under optimum gain conditions, emission occurs in single pulses, typically of a 10-8 second time domain. These pulses will have peak powers often in the range from 106 to 109 Watts peak.
        • REPETITIVELY PULSED or scanning lasers generally involve the operation of pulsed laser performance operating at a fixed (or variable) pulse rates which may range from a few pulses per second to as high as 20,000 pulses per second. The direction of a CW laser can be scanned rapidly using optical scanning systems to produce the equivalent of a repetitively pulsed output at a given location.
        • MODE LOCKED lasers operate as a result of the resonant modes of the optical cavity which can effect the characteristics of the output beam. When the phases of different frequency modes are synchronized ("locked together") the different modes will interfere with one another to generate a beat effect. The result is a laser output which is observed as regularly spaced pulsations. Lasers operating in this mode locked fashion usually produce a train of regularly spaced pulsations, each having a duration of 1015 (femto) to 1012 (pico) seconds. A mode locked laser can deliver extremely higher peak powers than the same laser operating in the Q-switched mode. These pulses will have enormous peak powers often in the range of 1012 Watts peak.

        Types of Laser

        • A simple laser consists of a lasing medium, an excitation system and an optical rescinator. The lasing medium can be solid, liquid, gas or a semi conductor.
        • It is the substance that is substance that is energized or excited in order to get its electrons to emit light into packets referred to as photons.
          • Examples of lasing mediums include
            • Carbon dioxide
            • Nitrogen gases
            • Solid ruby

        Excitation systems pump energy in the form of electricity or light into the lasing medium. When atoms in the lasing medium are excited, many of their electrons move to higher energy levels. As the electrons return to a lower energy level, they can emit photons. Many of the photons strike electrons that have also been excited. The collisions that occur cause other electrons to drop to lower energy states that emit more photons, and the process continues.
        Many photons travel along the optical access of the lasing medium. They would escape at both ends if it weren't for the optical rescinator.

        Optical rescinators consist of two mirrors placed in exact parallel and perpendicular positions to the optical access.
        Some of the photons that travel along the optical access of the lasing medium strike the mirrors and are reflected back. The reflected photons strike other excited electrons, creating an increase in photons. Because they are same wavelength traveling in the same direction, the photons add their energy together. The energy of the light wave is amplified, resulting in the intense light of the laser.
        In order for the light to escape from the lasing medium, one of the mirrors is made partially transparent.

        Helium Neon Lasers

        The first Continuous Wave (CW) system was the Helium Neon (HeNe) gas mixture. Although its first successful operation was at an infrared wavelength of 1.5μ, the HeNe laser is most well known operating at the red 633 nm transition. Some HeNe lasers today can also operate at other wavelengths (594 nm, 612 nm, 543 nm). Some earlier HeNe lasers were excited by radio frequency (RF) discharge, but virtually all HeNe lasers today are driven by small DC discharge between electrodes in the laser tube.

        The HeNe laser operates by an excitation of the helium atoms from the ground state. This energy excess is coupled to an unexcited neon atom by a collision process with the net result of an inversion in the neon atom population, thus allowing laser action to begin. Power levels available from the HeNe laser ranges from a fraction of a milliwatt to about 75 milliwatts in the largest available systems. The HeNe laser is noted for its high frequency stability and TEM(oo)(single mode) operation. The HeNe laser is one of the most widely used lasers in existence today. Its pencil thin beam is used in surveying work, to align pipelines, as a sawing guide in sawmills, and is also used to align patients in medical X-ray units, just to name a few of its many applications. It is also used in many retail scanners, lecture hall pointers, and display devices. In addition, holograms are often made using the coherent light of HeNe lasers.

        Argon, Krypton, and Xenon Ion Lasers

        This family of ion lasers utilize argon, krypton, xenon, and neon gases to provide a source for over 35 different laser frequencies ranging from the near ultraviolet (neon at 0.322μ) to the near infrared (krypton at 0.799μ). It is possible to mix the gases, argon and krypton for example, to produce either single frequency or simultaneous emission at ten different wavelengths ranging from the violet through the red end of the spectrum.

        The basic design of an ion gas laser is similar to the HeNe. The major difference is that the electrical current flowing in the laser tube will be 10-20 amperes: sufficient to ionize the gas. Population inversion is obtained only in the ionized state if the gas. An important feature of these lasers is the very stable (0.2%) high output power of up to 20 Watts/CW. Commercial models will normally have a wavelength selector (a prism) within the cavity to allow for operation at any one of the wavelengths available. In addition, approximately single frequency operation can be achieved by placing an etalon inside the optical resonator cavity.

        Argon ion lasers produce the highest visible power levels and have up to ten lasing wavelengths in the blue-green portion of the spectrum. These lasers are normally rate by the power level (typically 1-10 Watts) produced by all of the six major visible wavelengths from 458-514 nm. The most prominent argon wavelengths are the 514 and 488 nm lines. Wavelengths in the ultraviolet spectrum at 351 and 364 nm are available by changing resonator mirrors. To dissipate the large amount of generated heat, the larger argon ion laser tubes are water cooled. Although some lasers have separate heat exchangers, most use tap water.

        Simple pulsed versions of argon ion lasers are also available. Since the duty cycle ("on" time divided by the time between pulses) is low, the heat energy generated is small, and usually only convective cooling is needed. The average power output may be as high as several Watts, though the peak powers can be as high as several kilowatts. Pulse widths are approximately 5-50 microseconds, with repetition rates as high as 60 Hz.

        Carbon Dioxide Lasers

        The carbon dioxide laser is the most efficient and powerful if all CW laser devices. Continuous powers have been reported above 30kilowatts at the far infrared 10.6μ wavelength

        An electrical discharge is initiated in a plasma tube containing carbon dioxide gas. CO2 molecules are excited by electron collisions to higher vibrational levels, from which they decay to the metastable vibrational level. Establishing a population inversion between certain vibrational levels leads to lasing transitions of 10.6μ, while a population inversion between other vibrational levels can result in lasing transitions of 9.6μ. Although lasing can be obtained in a plasma tube containing CO2 alone, various gases usually added, including N2, He, Xe, and H2O. Such additives are used to increase the operating efficiency of CO2 lasers. The most common gas composition in CO2 lasers is a mixture of He, N2, and CO2.

        Carbon dioxide lasers are capable of producing tremendous amounts of output power, primarily because of the high efficiency of about 30%, as compared to less than 0.1% for most HeNe lasers. The principle difference between the CO2 laser and other gas lasers is that the optics must be coated or made of special materials to be reflective or transmissive at the far infrared wavelength of 10.6μ. The output mirror can be made of germanium, which, if cooled, has very low loss at 10.6μ.

        There are three common laser cavity configurations of the CO2 laser. The first is the gas discharge tube encountered with the discussion of the HeNe laser. Second is the axial gas flow, where the gas mixture is pumped into one end of the tube and taken out the other. The gas flow allows for the replacement of the CO2 molecules depleted (disassociated CO2 molecules) by the electrical discharge. Nitrogen is added to the CO2 to increase the efficiency of the pumping process and transfers energy by collisions. Associated effects enhance the de-excitation process. Helium is added to the mixture to further increase efficiency process of pumping and stimulated emissions. The third method is the transverse gas flow. This technique can produce CO2 laser emissions at power levels approaching 25 kW.

        The CO2 laser has a strong emission wavelength of 10.6μ. There is another strong line at 9.6μ and a multitude lines between 9 and 11μ. CO2 lasers are highly efficient (10-30%), give high output powers (used for welding cutting), and applications out of doors can take advantage of the low transmission loss atmospheric window at about 10μ.

        ND:YAG Lasers

        One of the most widely used laser sources for moderate to high power use a neodymium doped crystal Yttrium Aluminum Garnet (YAG), commonly designated Nd:YAG lasers. In addition, other hosts can be used with Ndm such as calcium tungstate and glass. The Nd:YAG laser is optically pumped by either a tungsten or a krypton pump lamp and is capable of CW outputs of approaching 200 W at the 1.06μ wavelength. The ends of the crystal (the crystal is usually in the shape of a rod) are lapped, polished, and may be coated to provide the cavity mirrors.

        • Nd:YAG lasers belong to the class of solid state lasers. Solid state lasers occupy a unique place in laser development. The first operational laser medium was crystal of pink ruby (a sapphire crystal doped with chromium); since that time, the term solid state laser has been used to describe a laser whose active medium is a crystal doped with an impure ion. Solid state lasers are rugged, simple to maintain, and capable of generating high powers.
        • Although solid state lasers offer some unique advantages over gas lasers, crystals are not ideal cavities or perfect laser media. Real crystals contain refractive index variations that can distort the wavefront and mode structure of the laser. High power operation causes thermal expansion of the crystal that alters the effective cavity dimensions, and thus, changes the modes. The laser crystals are cooled by forced air or liquids, particularly for high repetition rates.
        • The most striking aspect of solid state lasers is that the output is usually not continuous, but consists of a large number of often separated power bursts. Normal mode and Q-switched solid state lasers are often designed for a high repetition rate operation. Usually the specific parameters of operation are dictated by the application.
        • For example, pulsed YAG lasers operating 1Hz at 150 Joules per pulse are used in metal removal applications. As the repetition rate increases, the allowable exit energy per pulse necessarily decreases. Systems are in operation which can produce up to 10 Joules per pulse at a repetition rate of 10Hz. A similar laser, operated in Q-switched mode, could produce 1 megawatt per pulse at a rate of up to 10 pulses a minute

        Excimer Lasers

        High power ultraviolet (UV) lasers have been the desire of many in the laser applications community for over twenty-five years. Theoretically, such a laser could produce a focused beam of sub-micrometer size, and therefore, be useful in laser microsurgery and industrial microlithography. Also, photochemical processes which are dependent on shorter UV wavelengths would be possible at significantly greater speeds because of the enormous UV photon flux presented by a laser beam.

        • In 1975 the first family of new UV laser devise was discovered by Searles and Hart. This type of laser was to be referred to as an excimer laser, an abbreviation for the term excited dimmer. It took about a decade for these devices to move from the development lab into real world applications.
        • Excimer lasers operate using reactive gases such as chlorine and fluorine mixed with inert gases like argon, krypton, or xenon. The various gas combinations, when electrically excited, produce a pseudo molecule (called a dimmer) with an energy level configuration that causes the generation of a specific laser wavelength emission which falls in the UV spectrum. The reliability of excimer lasers has made significant strides over the past several years. Now, systems operating at average powers of 50-100 Watts are commercially available. A typical excimer operates in a repetitively pulsed mode of 30-40 ns pulses at pulse rates up to 50Hz with pulse energies of 1-2 Joules per pulse. Some systems use X-rays to pre-ionize the excimer laser's gas mixture, so as to enhance the lasing efficiency and increase the overall output power.
        • Until the late 1980s, excimer lasers were more commonly found in the research laboratory where they were used either as a specific UV source or, in many cases, to serve as a "pumping" or exciting source to generate visible laser emissions. In the latter case, the excimer's UV output was directed into a tunable dye laser or Raman shifter module and converted into a modestly high power visible frequency emission.
        • Excimer lasers are now making the transition from the lab to the production area for a few unique uses in industry, and in the operating room for exploratory surgical applications.

        Semiconductor Lasers

        The semiconductor or diode injection laser is another type of solid state laser. The energy level scheme is constructed by charge carriers in the semiconductor. They may be pumped optically or by electron beam bombardment, but most commonly, they are pumped by an externally applied current. Although all of these devices operate in the near infrared spectral region, visible laser diodes are being made today.

        1. Gallium Arsenide
        2. Gallium Aluminum Arsenide
        3. These lasers use very small diodes to produce a highly efficient source of laser light.

        Other Lasers

        Dye Lasers were the first true tunable laser. Using different organic dyes, a dye laser is capable of producing emission from the ultraviolet to near infrared. Most are operated in the visible with tunable emissions of red, yellow, green, or blue laser emission at almost any wavelength. The more common organic dye lasers are optically pumped. The most common dye used is Rhodamine-6G in solution. Such lasers may either be flashlamp pumped, or more commonly pumped with another laser such as an Argon or Nitrogen laser. To obtain CW reliable operation the dye is made to flow through a thin cell. Using the appropriate dye solutions, as argon-ion laser as a pump, and a prism, the dye laser is tunable across most of the visible spectrum. Tunable dye lasers are now widely used in high resolution atomic and molecular spectroscopy.

        Laser Wavelengths by Type in Nanometers

        Alexandrite 755
        Argon 457 476 488 514
        Carbon Dioxide 10,600
        Copper Vapor 511 578
        Erbium : Glass 1540
        Gallium - Arsenide 905
        Helium - Neon 633
        Krypton 351 356 530 647
        Neodymium : Yag 1064  
        Nitrogen 337
        Ruby 694

        Control Measures and Engineering Practices

        Amherst College shall, under the direction of the Radiation Safety Committee, the Laser Safety Officer or his/her designee shall, to the best of their ability, reduce the possibility of exposure of the eye and skin to hazardous levels of laser radiation and other hazards associated with the laser, laser systems or laser operations and maintenance.

        Laser and Laser Systems must be placed, set up, maintained and used in an "approved" and safe manner in accordance with manufactures specifications. A total hazard evaluation must be done by the Laser Safety Officer, his/her authorized designee, the Chemical Hygiene Officer, and/or Environmental Health & Safety, and shall be performed specifically for the Classification of Laser.

        The Laser Safety Officer can exceed, but can not be less stringent than that which is required by regulatory requirements which is specified in the applicability section when performing the Total Hazard Evaluation. Both property and more importantly personnel exposure to hazardous laser radiation shall be taken into consideration when the Total Hazard Evaluation is conducted.

        For all uses of lasers and laser systems, the "Authorized Operator" shall minimize the laser radiation required for the laser being used as much as practical for the work to be performed.

        The beam height shall be maintained at a level other than the normal position for the eye of a person in the standing or sitting position.

        Engineering Controls

        1. Engineering controls, whenever possible should be used to prevent illness, injury, and property damage and to limit access to laser radiation
        2. Enclosure of the laser equipment or beam path is one of the most effective means of limiting exposure to laser radiation.
        3. If Engineering controls are in practical or insufficient, other controls may be required, as directed by the Radiation Safety Committee, Laser Safety Officer and/or their designee. Other controls that may be applicable would include:
          • Administrative controls
          • Procedural Controls
            • "No person shall enter the facility unless."
          • Personal Protective Equipment

        Control Measures for Lasers

        The following engineering, administrative and procedures controls shall be implemented and enforced in accordance with the Amherst College Laser Safety Standard Operating Guidelines. The control measures identified here-in are laser class specific.

        n/a No requirement
        ® Shall (Required)
        * Shall if enclosed Class IIIb or IV
        MPE * Shall if MPE is exceeded  
        NHZ Nominal Hazard Zone Analysis Required  


        Engineering Controls I IIa II IIIa IIIb IV
        Protective Housing ® ® ® ® ® ®
        No Protective Cover or Housing Alternative Controls are established by the Laser Safety Officer
        Protective Cover or Housing - Interlocks ® ®
        Service Access Panel - Interlocks ® ®
        Access Control n/a n/a n/a n/a ®
        Viewing Points n/a MPE MPE MPE MPE MPE
        Access Control n/a n/a n/a n/a ®
        Collecting Optics MPE MPE MPE MPE MPE MPE
        Beam Path Open n/a n/a n/a n/a ® NHZ ® NHZ
        Beam Path Limited Opening n/a n/a n/a n/a ® NHZ ® NHZ
        Beam Path Enclosed None if Protective Housing requirements are fulfilled.
        Remote Interlock Connection n/a n/a n/a n/a ®
        Beam Stop or Attenuator n/a n/a n/a n/a ®
        Laser in Use - Warning Systems n/a n/a n/a n/a ®
        Emission Delay n/a n/a n/a n/a n/a ®
        Laser Controlled Area - Indoor n/a n/a n/a n/a ® NHZ ® NHZ
        Laser Controlled Area - Class 3b Indoor n/a n/a n/a n/a ® n/a
        Laser Controlled Area - Class 4 n/a n/a n/a n/a n/a ®
        Laser Controlled Area - Outdoors n/a n/a n/a n/a ® NHZ ® NHZ
        Laser Controlled Area - Temporary ◘ MPE ◘ MPE ◘ MPE ◘ MPE n/a n/a
        Firing and Monitoring - Remote n/a n/a n/a n/a n/a
        Labels, Warnings, and Signage ® ® ® ® ® ®
        Laser Area - Posting n/a n/a n/a ® NHZ ® NHZ
        Administrative and Procedural Controls
        Amherst College Standard Operating Guidelines n/a n/a n/a n/a ®
        Output Emission Limitations n/a n/a n/a Determined by Laser Safety Officer
        Education and Training n/a n/a ® ®
        Authorized Personnel n/a n/a n/a n/a ® ®
        Alignment Procedures n/a n/a ® ® ® ®
        Protective Equipment n/a n/a n/a n/a ®
        Spectator n/a n/a n/a n/a ®
        Service & Repair Personnel ◘ MPE ◘ MPE ◘ MPE ◘ MPE ® ®
        Laser Optical Fiber Systems MPE MPE MPE MPE ® ®
        Laser Robotic Installations n/a n/a n/a n/a ® NHZ ® NHZ
        Eye Protection n/a n/a n/a n/a ♦ MPE ® MPE
        Protective Windows n/a n/a n/a n/a ® NHZ ® NHZ
        Protective Barriers and Curtains n/a n/a n/a n/a
        Skin Protection n/a n/a n/a n/a ® MPE ® MPE
        Personal Protective Equipment Use may be required.
        Warning Signs and Labels (Design Requirements) n/a n/a ® NHZ ® NHZ
        Service and Repairs Determined by Laser Safety Officer.
        Modifications and Laser Systems Determined by Laser Safety Officer.

        Laser Area Warning Labels and Signage

        In accordance with all applicable regulatory agencies, including, but not limited to, Nuclear Regulatory Commission (NRC), the Occupational Safety and Health Administration (OSHA), the Massachusetts Department of Public Health, and Amherst College policies, which include ANSI and NFPA standards, appropriate labels and signs shall be posted to properly warn affected persons about the health and safety hazards inside the laser control area, or with a specific laser, laser system, or part thereof.

        Warning labels and signs should appear on or around

        1. Doors entering into facility or building when appropriate
        2. Nominal hazard zones
        3. Barriers, curtains, screens
        4. Lasers and laser systems
        5. Parts of a laser or laser equipment that can be defeated, such as interlocks
        6. Other appropriate laboratory equipment
        7. Chemicals

        Amherst College requires the posting of proper warning labels and signs on all doors that allow access to rooms or areas that contain IIIa, IIIb, and IV lasers. These areas include, but are not limited to

        1. Classrooms
        2. Construction sites
        3. Laboratories
        4. Other areas or rooms where these classes of lasers are being utilized

        There are only two recognized laser symbol designs that are acceptable for use in accordance with Amherst College policy and ANSI standards

        1. ANSI Z 535 -Utilizes a sunburst pattern consisting of two sets of radial spokes of different lengths and one long spoke radiating from a common center
        2. IEC 60825-1 -Utilizes an equilateral triangle surrounding a sunburst pattern consisting of two sets of radial spokes of different lengths and one spoke radiating from a common center

        Laser warning labels and signs shall have signal words and be color coded in accordance with the regulatory requirements of OSHA. Wording for labels and signs shall be standardized in accordance with ANSI Z 136.1-2000, tables 11a and 11b (pages 53 and 54), and figures 1a-1d (pages 55-58). Signal words and applicable wording shall be:

        1. NOTICE- indicates Amherst College policy as the message relates directly or indirectly to personal health and safety. It shall not be used in place of Caution, Warning, or Danger where death or severe injury may occur.
        2. CAUTION- indicates hazardous conditions or situations which may result in minor or moderate injury. It shall not be used in place of Warning or Danger.
        3. WARNING- indicates hazardous conditions or situations which have some probability of death or severe illness or injury. It shall not be used in place of Danger or Property Damage unless a personal risk injury or illness is present.
        4. DANGER- indicates an imminently hazardous situation which, if not avoided, could result in death or serious illness or injury with high probability. Its use shall be limited to the most extreme conditions.
        • Low Irradiance Lasers-yellow and black Caution label
        • High Irradiance Lasers-red, black, and white Danger label

        Signage, including warning labels, shall be acquired through the laser manufacturer and should be specific to the laser purchased and used in that particular area. Signs can also be acquired through Amherst College Office of Environmental Health and Safety to insure compliance with OSHA standards.

        All signage must be conspicuously posted to properly warn persons that could be potentially exposed to the laser or laser systems

        • Only authorized and properly trained faculty, staff, students, invited guests, maintenance/service personnel should be provided access to the laser in accordance with Amherst College policies
        1. Persons who may have access, but are not authorized, shall be warned of the hazard through the use of appropriate signage before an incident occurs.
        • As a minimum, the following shall be included on signage:
        1. Laser protective eyewear required
        2. Invisible laser radiation (if applicable)
        3. Do not enter when light is on
        4. Restricted Area
        • For laser specific class, the following is required on signage
        1. Class II- Laser radiation, do not stare into beam
        2. Class IIIa - Laser radiation, avoid direct eye exposure
        3. Class IIIb - Laser radiation, avoid direct exposure to the beam
        4. Class IV - Laser Radiation, avoid eye or skin exposure to direct or scattered radiation
        • At position 2, below the tail of the sunburst, the type of laser (Nd: YAG, Helium - Neon, etc), or the emitted wavelength, pulse duration, and maximum output
        • At position 3, the class of the laser and laser system shall be indicated

        Audible/ Visible Signs

        Class IIIb and IV lasers shall have an audible alarm such as a bell, buzzer, chime, or horn, a warning light or other appropriate signal which is visible through protective eyewear, or a verbal countdown command for a single pulse or intermittent operations shall be used during activation or setup.

        The alarm for the start up of the laser should be distinctive and clearly identifiable.

        Amherst College classroom and laboratory lasers class IIIb and IV are clearly identified with signage located above the main door that indicates:

        Danger - Laser in Use

        1. The signs are red letters against a white background with flashing red lights on both sides of the sign.
        2. The College has also installed card access for the laboratories that use Class IIIb and IV lasers. These rooms will only be accessible to a person who has received the proper training and are authorized to be in a Class IIIB or IV laboratory facility.
        3. Card access will be regulated by the appropriate department, and shall information updated each semester, or as needed to insure appropriate access and proper security.

        Equipment Labels

        1. All lasers, laser systems, other equipment, and parts thereof requiring labels in accordance with manufacturer specifications, OSHA, NRC, and ANSI standards shall be conspicuously posted for hazard recognition purposes
        2. In the event of label loss, label deterioration, or obstruction of the warning, a replacement or alternative site location is required!
        3. Missing labels or other warning notices shall be considered a violation of OSHA standards'.

        Signs and Labels - Required Non Beam Hazard Warning Signs

        Signage warning of hazards unrelated to laser, laser beams, and laser systems shall be posted in accordance with the applicable OSHA regulations and associated standards.

        Hazard warnings for chemicals, compressed gas, electrical, fire, hazardous materials and waste shall be placed in close proximity to the actual hazard and/or on the door to the laboratory of facility when appropriate.

        Nominal Hazard Zone (NHZ)

        The Laboratory Safety Officer is responsible for establishing the Nominal Hazard Zone, where appropriate, such as in the presence of unenclosed Class IIIb and IV beam paths.

        The first step in calculating the NHZ is to determine the maximum permissible exposure (MPE).

        • The area surrounding the laser device where the MPE is exceeded is the NHZ.
        • The NHZ can be a large area. The size depends on:
          1.  Laser power
          2. Beam divergence
          3. Emergent beam diameter
          4. Characteristics of focusing lenses or reflective surfaces

        If the beam of an unenclosed Class IIIb or IV laser or laser system is within an area with engineering controls to protect personnel from exposure to levels of radiation above the maximum permissible emission limit, the area may be considered to contain the NHZ.

        The NHZ for lasers and laser systems may be determined using applicable information from the laser manufacture, by measurement, or by using the appropriate laser range equation or other appropriate assessment as described by manufacturer or Laser Safety Officer.

        Under no circumstance can the NHZ be made less safe or less restricted than that which is dictated by the manufacturer.

        The Laser Safety Officer shall be responsible for the laser control area and other applicable engineering controls taking direct, scattered and reflected radiation into consideration.

        General Safety Guidelines

        1. When using laser and laser systems, at least two persons should be working together in the laser facilities.
          • Working above, especially after normal business hours is strongly discouraged.
        2. Laser operators shall not work with laser or laser systems while under the influence of alcohol, drugs, or medications, including those sold over the counter that can cause drowsiness or fatigue.
        3. Laser operators shall not engage in activities that could result in illness or injury.

        Dye lasers utilize complex organic chemicals.

        1. Many of these dyes are considered to be toxic, and the documentation is limited.
        2. Some are considered to be mutagenic and capable of changing the genetic information in living cells.
        3. Some of the dyes, when mixed with dimethyl sulfoxide, are capable of penetrating the skin.

        Compressed Gases Used in Lasers

        1. Carbon Dioxide
        2. Carbon Monoxide 
        3. Halogens
          •  Halogen gases, such hydrogen chloride, hydrogen bromide, and fluorine are used with eximer lasers. These gases are both corrosive and toxic.
          • Gases may also be biologically inert buffer gases, like helium and argon, which are not toxic.
          • Proper exhaust ventilation is required for both dye and hazardous gases.
        1. Laser facilities using hazardous materials, like those referenced above, should be under at least a 10% negative pressure with respect to the corridor.
        2. General room exhaust or ventilation is not adequate. A local exhaust or capture type hood or gas cabinet is necessary.
        3. Canopy hoods are NOT acceptable.
        4. Care must also be taken when the laser beam comes in contact with a surface, such as plastic or vinyl. Hazardous gases can be generated at this point. Proper exhaust must be addressed for health and safety reasons.

        For High Powered Class IIIb and IV Lasers

        1. incorporate fault-current-limiting devices such as breakers, fuses, switches, or resistors, capable of clearing or dissipating total energy.
        2. Protect against projectiles or other moving objects that may be produced during faults by using barriers and enclosures specified by the manufacturer for that specific laser or laser system.
        3. Enclosures should be designed to prevent accidental contact with terminals, cables or exposed electrical contacts.
        4. Incorporate a grounded metal enclosure that is locked and/or interlocked.
        5. Reduce combustible storage in the facility to an absolute minimum.
        6. Properly store flammable liquids in approved containers, or in rooms or facilities outside the laser facility.
        7. Provide a short discharge time constant in the grounding system.
        8. Verify that each capacitor is discharged, shorted and grounded before allowing access to capacitor area.
        9. Verify reliable grounding, shorting and interlocking.
        10. Incorporate grounding switches, cables, and other appropriate safety devices that will withstand the mechanical forces that could exist when faults occur or crowbar currents flow.
        11. Install appropriate audible/visual warning devices, lights and signs in accordance with ANSI Standard Z136.1
        12. Provide shorting straps at each capacitor during maintenance repair or service while capacitors are in storage.
        13. Incorporate metal grounding equipment that has the connecting cable visible for its entire length.
        14. Install as necessary the appropriate safety devices such as personal protective equipment, eyewear, face shields, gloves and insulating mats.
        15. Provide metering, control and auxiliary circuits that are protected form possible high potentials even during fault conditions.
        16. Inspect capacitors for leaks
        17. Provide and properly train staff using a grounding stick that has discharge resistor at contact point, an insulated ground cable and grounding cable permanently attached to ground.

        Electrical Hazards

        Many laser systems contain high voltage supplies that can operate from 50 to thousands of volts.

        • The hazard from contact with an energized electrical system can depend on
          • Level of current
          • Path of current through the body
          • Environmental conditions such as humidity, flammable materials, and water
        • Any person working on a laser or laser system must be authorized and qualified.
        • Before working on a system like this, the repair or service personnel must perform proper lock-out/tag-out procedures as required by Amherst College policy.
        • Electrical Safety
        1. Laser operators shall remove jewelry such as rings, watch bands, and other metallic objects.
        2. The use of only one hand (when possible) if working on a circuit or control device is strongly recommended.
        3. The laser operator should not handle equipment that is electrically energized if any portion of their body, or the area they are located in is wet.
        4. Consider all floors conductive and grounded unless covered with an appropriate, well maintained dry matting, approved by the manufacturer for that type of laser or laser system, when suing high voltage electrical equipment.
        5. Verify the location of all emergency shut-down procedures to be used in cases of shock or electrocution. This protocol must be part of the training process for all potential laser operators.

        Emission Limitations

        The Laser Safety Officer or his designee shall be responsible for controlling excessive power or radiant energy during maintenance and operation activities of a Class IIIa, IIIb, or IV laser or laser systems.

        1. The LSO shall take action as necessary to reduce the levels of accessible power or radiant energy for the type of work being performed.
        2. Power shall be reduced to the absolute minimum when beam adjustments are being performed for reasons of health and safety.

        Indoor Laser Operations

        For Indoor operations of lasers and laser systems such as classrooms, laboratories, carpentry and mechanical related work, the following procedures (in order) shall be followed for the establishment of the NHZ and to protect faculty, staff, students, and other authorized personnel from a potential for exposure. The evaluation must take into account lenses, mirrors, fiber optics, warning and danger signage and personal protective equipment which are part of, or an integral piece of the laser beam path.

        1. Include multi-beam paths when lack of fixed positioning and unintended beam paths due to loose or unsecured mounts, bearing wear, vibration and improper placement is possible.
          • The power used for laser and laser systems during a demonstration, display, or performance shall be set at the level necessary to produce the desired or intended effect.
        2. Evaluate the NHZ for all possible beam paths.
        3. Evaluate the NHZ for specular reflections.
        4. Authorized Operator shall determine the extent of hazardous diffuse reflections if the emergent laser beam is focused.
          • Hazardous diffuse reflections are possible from a focused or small-diameter beam of a Class IIIb laser.
            • The angular subtense of the source is normally small at all practical viewing distances that Small Source Maximum Permissible Exposures will apply.
            • Determine the Nominal Hazard Zone (NHZ)
        5. Authorized Operators shall determine whether or not the beam will visually interfere with critical tasks.
          • Protocols are modified when using laser systems outdoors at night.
            • See Outdoor Laser Operations section and ANSI Standards Z136.6
        6. Authorized Operators shall determine by hazard assessment, the possibility of custodial or maintenance personnel being in the Nominal Hazard Zone during operation.
          • In accordance with the Amherst College Laboratory Entry Policy, no Amherst College personnel or outside contractor shall have entered any laboratory, inclusive of laser laboratories without first obtaining the permission of:
            • Laboratory Principal Investigator (Professor Responsible)
            • Chemical Hygiene Officer
            • Environmental Health & Safety Officer Manager
        7. Laboratory personnel familiar with the laboratory and equipment shall, prior to laboratory or laser utilization determine and correct as appropriate any hazard that could cause personal illness or injury and/or damage to property
        8. Laser Beam Termination
          • All lasers and laser systems used for performances and demonstration purposes shall be equipped with an accessible method of shut-down in cases of emergency
          • If the demonstration, display, or performance is not required to be continuously supervised, or under direct authorized operator control during the performance or display, then a trained, designated, responsible person shall be required to terminate the laser, laser beam, or laser system in case of equipment malfunction or other unsafe condition.
        9. Laser Power - Displays and Performances
        10. Class IIIb laser areas shall
          • Be set up in such a way as to prevent unauthorized access to the area
            • Doors to the area shall be self closing and latching in a locked mode
            • Classroom or passage lock systems cannot be used
          • Have potentially hazardous beams terminated in a beam stop using the appropriate and approved material
          • Have only diffusely reflecting materials in or near the beam path, when appropriate
          • Have the appropriate personal protective equipment available, including ANSI approved eyewear specified in ANSI Z87.1-1989
          • Have the laser secured in such a way that exposed beam path is either above or below the eye level of any area occupant who is either standing or sitting.
            (Exception - medical use)
          • Have all windows, doors, and other potential exposure sites covered or restricted in such a manner as to reduce the transmitted laser radiation to levels below the MPE
          • Have a means to render the laser disabled when not in use to prevent unauthorized operation
        11. Class IV areas shall meet all the requirements of a Class IIIb laser and in addition
          • Be set up to allow emergency egress, in cases of emergency, without delay or hazard
          • Require training, including the selection types, uses and safe operating procedures, the use of personal protective equipment, administrative and any applicable procedural controls for the classes of lasers to be used, maintained, repaired, or serviced.
          • Whenever appropriate, Class IV lasers and laser systems shall be controlled and monitored at position as distance from the emission as possible.

        Optical Fiber Transmission Systems

        Transmission systems for lasers that use optical cables and fibers are enclosed systems because the cable forms the enclosure.

        1. If disconnection of a connector reduces accessible radiation below MPE through engineering controls, connection or disconnection may take place in an uncontrolled area and not other control measures are required.
        2. when the laser or laser system allows access to laser radiation above the applicable MPE through a connector, then the following shall apply.
          • During laser operation, connection, or disconnection shall take place in the appropriate laser control area.
          • During maintenance, modification, repair, or service, connection or disconnection shall take place in a temporary laser controlled area.
            • When the connection or disconnection is made by means of a connector, other than one within a secured enclosure, such a connector shall be disconnected only by the use of a tool.
        3. Class IIIb and IV lasers or laser systems shall not be disconnected before termination of transmission of the beam into the fiber.
          • If laser radiation accessible by disconnection of a connector, the connector shall bear a label or warning tag with the following wording.
            • "Hazardous Laser Radiation when Disconnected"
        4. Appropriate procedures should be set up by the LSO to prevent accidental exposure to personnel form a broken or un-terminated fiber, such as lock and tag requirements at the laser source.
        5. No tools for connector disconnection are required when the connection or disconnection is made within a secured enclosure.

        Class IIIb and IV Laser Robotic Installations

        When lasers and laser systems are used in connection with robots, the robot working area shall be included in the NHZ. When the beam is focused by a lens associated with the robotic device, then the appropriate safeguards will work provided:

        1. Positive beam termination control measures have been designed into the operation of the laser.
        2. The beam geometry is limited to the work area only
        3. Personnel are located at a distance greater than or equal to the lens-on laser NHZ value for the laser robotic system.

        In case of equipment malefaction, hardware failure or software abnormalities, the laser beam from the robotic system can be deflected at angles that could lead to potential scattering that must be completely evaluated NHZ must be properly measured to confirm appropriate boundaries.

        Outdoor Laser Operations

        Outdoor laser operations must be approved (in advance) by the Laser Safety Officer.

        Navigable Air Space

        • If an Amherst College Class IIIa, IIIb, or IV laser is used in navigable air space, which is regulated by the Federal Aviation Administration (FAA), the department responsible shall contact and coordinate with the FAA prior to the utilization of the equipment.
        • The FAA has regional offices, or can be contacted on-line for additional information and regulatory requirements.

        A complete hazard assessment of the specific laser system will depend on several potentially hazardous conditions. The Authorized Operator and the Laser Safety Officer shall consider all optics during the evaluation because they are part of the laser beam path. Lenses, mirrors, fiber optics etc must be addressed.

        The following steps should be performed:

        1. Identify the Nominal Hazard Zone of the laser.
        2. The Authorized Operator must evaluate potential hazards from the transmission of the laser beam through windows as well as specular reflections. Specular surfaces such as mirrors and windows of buildings and vehicles are oriented vertically and will usually reflect a horizontally aimed beam.
          • Care should be taken whenever there is a possibility of a beam striking a specular surface such as 8% of the beams original irradiance or radiant exposure can be reflected back to the laser off any reflective surface.
        3. Look for the possibility of hazardous diffuse reflections and determine what the Nominal Hazard Zone shall be.
        4. Evaluate the stability of the laser platform(s) to determine the extent of the lateral range control and the lateral constraints that should be placed on the laser beam transverse.
          • What will the Nominal Hazard Zone be?
        5. How will the Authorized Operator and Laser Safety Officer prevent unauthorized access into the Nominal Hazard Zone.
        6. Because laser irradiance as low as 50nWcm2 can be of concern to airports and similar operations, the authorized operator shall, in advance contact the Federal Aviation Administration or other applicable agency before using the laser.

        Control Measures for Personnel

        Personnel who may be affected by, or in the vicinity of the laser and the emitted beam(s) can influence the hazard assessment performed by the authorized operator and/or the laser Safety Officer.

        1. Policies and procedures, including the appropriate engineering controls, shall be incorporated into the evaluation process to reduce the risk of personnel illness, injury or property damage.
        2. It is the responsibility of the Authorized Operator, Laboratory Principle Investigator and/or the Laser Safety Officer to mitigate any known or potential hazards.
        3. Warning signs and labels shall be posted visible, and shall properly indicate the degree of hazard. Affected persons must be able to recognize and understand the signs and labels, or more appropriate restrictive measures will be required.

        Laser Operation without Protective Cover or Housing

        At certain times, with accordance with manufacturer's specifications, laser and laser systems can be operated without a protective housing or covering.

        Under these circumstances, the laser safety officer must ensure that control measures be utilized that are appropriate for the class of laser. These control measures may include, but are not limited to the following:
        1. Designation of a laser controlled area.
        2. Appropriate personal protective equipment
        3. Placement of beam stops, curtains, and shrouds.
        4. Administrative controls
        5. Procedural controls
        6. Training and education

        Interlocks on Lasers with Removable Covers and Housings

        Class IIIb and IV lasers shall have a functional interlock system that is activated when the protective cover or housing is opened or removed for maintenance or service.

        1. The interlock may be electronically or mechanically connected to a shutter that interrupts the beam when the cover or housing is opened or removed.
        2. The protective cover or housing interlock shall not be defeated or overridden during operation unless a alternative safety measures, such as engineering or administrative controls sanctioned by the laser safety officer, are in place and functional.

        Laser Access Panels

        When appropriate parts of the protective cover or housing are removed from the laser or laser system by service personnel that permits direct access to laser radiation with a Class IIIb or IV laser, then the laser shall either

        1. Be interlocked

        Laser Primary Control

        Class IIIb and IV lasers or laser systems shall have a main switch. The switch shall control beam termination and/or system shut-off. It should be operated by an authorized operator with a key or access code.

        1. Keys shall not be left in the main or primary control unless an authorized operator is present.

        The primary energy source for a class IIIb and IV laser shall be designed to accommodate lockout/tagout procedures that are required by OSHA.

        Viewing Points, Windows, and Diffusing Display Screens

        Viewing points, windows, diffuse display screens, and laser barriers are protective devices that can be incorporated into a laser or laser system.

        These protective devices, which are an integral part of a laser or laser system, shall have in place suitable interlocks and filters. Attention shall be given to maintain the laser radiation at the viewing position at or below the maximum permissible exposure.

        These protective devices must be appropriate for the laser or laser system in accordance with the manufacturer's specifications.

        1. Safeguards should be built in to windows, viewing points, and/or display screens to prevent decomposition and the generation of airborne contaminants, and to insure personal health and safety.


        Collecting optics (which include lenses, telescopes, microscopes, endoscopes, etc.) that are intended to be used with lasers and laser systems for viewing purposes shall have suitable filters, interlocks, and maintenance of laser radiation transmitted through the collecting optics to levels at or below maximum exposure levels.

        Laser Alignment & Beam Paths

        Alignment of Class IIa, II, IIIa, IIIb, and IV lasers shall be...

        1. Performed by authorized persons
        2. Performed in a manner that will not expose eyes to levels above the applicable MPE for the primary specular or diffuse reflection of a beam
        3. Performed with all appropriate health and safety controls in place
        4. When applicable, performed in accordance with manufacturer's specifications, and under the guidelines of the LSO.
        5. Performed using the lowest possible power recommended for alignment of the higher power Class IIIb and IV laser or laser systems.

        Laser beam paths be controlled in the following manner for Class IIIb and IV lasers...

        1. Fully Open-a laser hazard analysis shall be performed by the laser safety officer when a beam path is unenclosed in order to establish appropriate safety controls and NHz (see manufacturer's specifications).
        2. Limited Opening-for Class IIIb and IV lasers or laser systems where the beam path is limited by design to significantly reduce the ability to access the open beam.
          • The laser safety officer shall perform the hazard analysis and determine the necessary health and safety controls to be used to prevent laser radiation from reaching the maximum permissible exposure.
        3. Enclosed-when the entire beam path of the laser or laser system is completely enclosed, all requirements for protective covering and housing have been met.
          • If the protective covering and housing controls must be compromised for service, the laser safety officer, or this designee, shall incorporate other engineering, administrative, or procedural control for the health and safety of the approved service technician and other potentially affected persons.

        Interlock Connection-Remote

        Class IIIb and IV lasers or laser systems shall have a remote interlock connector. This connector will tie the electrical connectors to an emergency master disconnect interlock.

        If the terminals of the connector are "open," the accessible radiation shall not be able to exceed maximum permissible exposure levels.

        Beam Attenuators and Stops

        Class IIIb and IV lasers and laser systems shall have a permanently attached beam attenuator or stop.

        The beam attenuator or stop shall be capable of preventing access to laser radiation in excess of the maximum permissible exposure level when the laser or laser system output is not required, such as during equipment set up.

        Work Space

        Sufficient room shall be provided for the reasons of health and safety when using lasers and laser systems. The authorized operator, under the direction of the LSO shall sollow manufacturers specifications and ANSI Standards for proper compliance.

        • Electrical hazards shall be labeled and protected from possible contact.
        • Housekeeping shall be maintained to eliminate incidents involving fire and injury.
          • Combustible and flammable materials shall be kept to an absolute minimum and "means of egress" shall be properly maintained at all times.

        Personal Protective Equipment (PPE)

        Engineering Controls such as complete laser beam and equipment enclosure shall be the primary method of control to minimize health and safety hazards.

        1. When engineering controls do not provide adequate protection, or when normal engineering controls are not practical to prevent access to direct or reflected beams at levels above the MPE, then Personal Protective Equipment, including the appropriate eye protection such as spectacles, goggles, face shields, that meet the requirements of ANSI Standard Z87.1-1989 Additionally, barriers, windows, clothing, gloves, and other appropriate protective devices which are specifically applicable to the laser, laser beam or laser systems must be in place in other to provide protection against laser radiation
          • Low irradiance Class IIIa lasers can be considered a hazard if you view the beam directly for more than ¼ second without using an optical instrument, or if you do use an optical instrument and view the beam for more than ¼ second.
            If you look directly into the beam of a class IIIa high irradiance laser, you could be subject to an acute viewing hazard.
        2. Personal Protective Equipment for high-powered, Class IV lasers or laser systems shall be appropriate for the hazards associated with a Class IV laser.

        Eye Structure and Laser Hazards

        The eye is the sensory organ that responds to light

        • Light enters through the transparent outer surface of the eye, which is the cornea
        • The cornea and the lens focus the light onto the retina on the back interior surface of the eye.
        • Focusing concentrates on a small area, which increases the irradiance at the retina. When looking directly at an object, the eye focuses the light on the macula, a small area of the retina.
          • The center of the macula (fovia) is the part of the eye responsible for clear and critical vision. The light strikes the photoreceptors, which create an electrical impulse. This signal is passed on to the neural network to the visual cortex of the brain, where the visual signals are interpreted.
          • The optics of the eye increase the irradiance of incoming light by a factor of 100,000-150,000, which has the potential to cause serious eye injury.

        Acute Viewing

        • Viewing laser radiation for < ¼ second (Aversion Response Time)
          •  Class II lasers are not considered acute viewing lasers because of hazard severity and aversion time.
        • Chronic Viewing
          •  Viewing class II lasers for > ¼ second can be hazardous and is considered chronic viewing.


        The laser protective eyewear selected must be able to withstand either a direct or diffusely scatted beam. Protective eyewear shall be evaluated and purchased to withstand a "worst-case" exposure scenario.

        1. Wearers of the protective eyewear referenced above should ask for the test data form the laser eyewear manufactures.

        High Powered Lasers

        There are two classes of high powered lasers. Both can be "pulsed" or "CW," and the radiation can be either visible or invisible.

        1. IIIb
          • IIIb CW lasers range in power up to ½ Watt.
        2. IV
          • IV lasers power greater than ½ Watt.

        Skin Protection for Class IIIb and IV lasers

        Skin cover shall be required if repeated exposures are anticipated for laser operations such as eximer lasers that are operated in the ultraviolet mode (295 - 400 nm) and/or laser cutting or welding operations. Examples of appropriate skin protection would include:

        1. Gloves as recommended by ANSI and by manufacturer
        2. Sunscreen of adequate protection factor
        3. Tightly woven fabric clothing or covering
        4. Laboratory coat or jacket
        5. * For Class IV Lasers flame retardant materials such as Nomex shall be used. * Chronic (long term or frequent) exposure may cause adverse health effects that are not yet completely known.

        Additional Equipment for Laser Facilities

        Adequate ventilation shall be provided as the most appropriate engineering control for fumes, smoke and particulates generated by lasers and laser systems.

        1. If adequate exhaust is not practical then respiratory protection can be provided.
          • In order to obtain and wear the appropriate respiratory protection, the authorized operator must undergo a medical examination, pulmonary function test and respirator fit test as required by OSHA and the Respiratory Protection Policy of Amherst College. See the Amherst College Environmental Health & Safety website for additional details and requirements.
        2. Dye laser hazards and compressed gases.

        Hearing Protection as required by the Occupational Safety and Health Administration (OSHA)

        Personal Protective Equipment - Ultraviolet Laser

        When using ultraviolet light laser and laser systems, the following requirement shall apply:

        1. Beam shields and clothing which alternate the radiation levels below the MPE for specific UV wavelengths shall be used to minimize exposure to UV radiation.
        2. The hazard assessment shall take into consideration other potential health and safety concerns such as skin sensitizing agents and ozone.

        Personal Protective Equipment (PPE) shall be used when personnel are working with a Class IIIb or IV UV laser with an open beam. The PPE shall include eye, face and skin protection.

        Protective eyewear, including prescription and safety glasses, goggles and face shields for the protection of eyes, unrelated to lasers shall comply with the ANSI Standard Z87.1-1989.

        Protective eyewear for lasers must be appropriately selected, and shall take into consideration the following "worst case" concerns:

        1. Laser power and/or pulse energy
        2. Wavelengths of laser output
        3. Potential for multi-wave operation
        4. Radiant exposure or irradiance levels
        5. Exposure time
        6. MPE (eye and skin)
        7. Optical density requirement of eyewear filters at laser output wavelengths
        8. Angular dependence of protection afforded
        9. Visible light transmission requirement and assessment of the effect of the eyewear on the ability to perform tasks while wearing the eyewear
        10. Need for side shield protection and maximum peripheral vision requirement
        11. Radiant exposure or irradiance and the corresponding the factors at which laser safety filter characteristic change occurs, including transient bleaching, especially for ultra short pulse lengths.
        12. Comfort and fir
        13. Degradation of filter media, such as photo bleaching
        14. Strength of materials (impact and exposure) as referenced in ANSI Z87.1-1989
        15. Compatibility of the front surface to produce a hazardous specular reflection
        16. Antifog design or coating.

        Filter Material - Optical Density

        When determining the optical density of a filter material, the length of use for the laser or laser system shall be taken into consideration. The following are ANSI Recommendations are applicable when the determinations are being made:

        1. Aversion Response Criteria to Visible Class IIIb and IV lasers (0.4-0.7μm)
          • If long term exposure to visible lasers is not intended, to applicable MPE used to establish the optical density requirements for eye protection should be based on an exposure time of 0.25 seconds.

        Near - Infrared (Class IIIb and IV) Controls

        When long term exposure to near-infrared (0.7-1.4μm) lasers is not intended, the applicable MPE used to establish the optical density requirement for eye protection should be based on a 10 second exposure. This would be considered "worst case" time period because natural eye motion dominate for periods longer than 10 seconds.

        Diffuse Viewing (Class IIIb and IV) Criteria

        When viewing an extended source or the diffuse reflection of the beam from a Class III or IV laser or laser beam system where intermediate viewing time is intended, for optical alignment procedures, the applicable MPE should be based upon the maximum viewing time which may be required during any given 8 hour period.

        When long-term exposure to visible (0.4 - 0.7μm) CW lasers is not specifically intended, the applicable MPE used to establish the optical density requirement for eye protection may be based on a 600-second exposure. This would be a "worst case" time period during tasks such as alignment and is applicable for most alignment procedures when viewing a diffusely reflecting target. In some situations where staring is anticipated, such as during a surgical procedures, even longer times should be considered, during the hazard assessment, based on actual conditions of use.

        Daily Occupational Exposure Criteria for Class IIIb and IV

        A full one day (8 hour exposure) = 30,000 seconds

        1. Within a 24 hour time period, the maximum time of expected direct exposure should not exceed 30,000 seconds, except for ultraviolet light.
        2. When long term exposure to any laser is possible, the applicable MPE used to establish the optical density requirement for eye protection shall be based on a 30,000 second (8 hr) exposure.

        Optical Density - Now Laser Emissions

        ANSI approved eye protection shall be provided for the ultraviolet and blue-green spectral region (0.18-0.55μm) for laser welding processes. A minimum optical density of 2.3-3.0 (neutral density) or welding shade 6 is recommended for emission in the ultraviolet and blue-green spectral regions.

        1. The optical density values given above would apply for laser induced plasma, such as a laser welding system.
        2. Greater optical densities are required for higher power laser welding systems.

        All protective eyewear must be clearly labeled with the optical density and wavelengths for which protection is afforded.

        1. Color coding or other distinctive identification of laser protective eyewear is recommended in multi-laser environments.
        2. Protective eyewear shall meet the requirements, and be labeled in accordance with ANSI Z-87.1-1989

        Protective eyewear shall be cleared and inspected. At a minimum eyewear should be checked for breaks, cracks, discoloration, pitting, and structural abnormalities and other obvious deficiencies whenever worn. A very thorough evaluation of all eyewear should be performed annually, as recommended by the manufacturer, or more frequently, if required by the LSO.

        1. The Cleaning of protective eyewear for lasers shall be performed in accordance with manufactures specifications.

        Protective Eyewear - Purchasing

        Protective eyewear shall be evaluated and purchased with the following criteria taken into consideration.

        1. Manufactures recommendations and shelf life as applicable to that laser.
        2. Wavelengths and corresponding optical density for which protection is afforded.
        3. Pertinent data such as damage threshold for laser safety.

        Protective Equipment – Installations

        Window Protection - Class IIIb and IV Laser Facilities

        For any windows in classroom, laboratory and other laser facilities, which are located in the NHZ of a Class IIIb and IV Laser and laser system shall have the appropriate absorbing filter, scattering filter, blocking barrier, or screen which reduces any transmitted laser radiation to levels below the MPE level.

        The windows shall be able to withstand both direct and diffusely scattered laser beams.

        1. The window barrier or filter shall be able to exhibit a damage threshold for beam penetration for the specified exposure time as determined by the LSO during the hazard evaluation.
        2. When selecting windows for laser areas, the LSO and other applicable personnel shall take into consideration
          • Decomposition
          • Flammability
          • Structural Integrity
          • Past performance for similar applications
        3. In accordance with the requirements of the Massachusetts Building Code (780 CMR), the windows chosen shall not support combustion, nor shall it create the release of an airborne toxin following laser exposure.

        Window Barriers and Curtains for Class IIIb and IV Lasers and Laser Systems

        In order to prevent laser light or beams form exiting the laser area through a door or window, a blocking barrier, curtain or screen shall be installed inside the controlled area in a manner not easily defeated.

        • The LSO must conduct a hazard evaluation, including the NHZ to assure the health and safety of person both inside and outside the controlled area.
        • The LSO and other applicable personnel involved in the process of selecting barriers, curtains and screens shall verify that the material used will not be combustible and/or create fumes when exposed to the laser beam.
        • All laser protective barriers, curtains and screens shall bear the appropriate label that includes the threshold limit and exposure time for the laser or laser system being used, in accordance with manufactures specifications laser system being used, in accordance with manufactures specifications.

        Laser Protective Windows - Labeling

        Laser protective, barriers, curtains and screens shall be labeled with the appropriate information such as optical density and wavelengths for the laser or laser system being used, in accordance with manufactures specifications or the LSO's hazard evaluation (more stringent shall apply). All laser protective windows shall be labeled with the threshold limit and exposure time applicable to that site specific laser.

        Collecting Optics Filters- Labeling

        Permanently mounted ceiling optics housing containing laser protective filters shall be labeled with the optical density and wavelengths. The collecting optics filter housings shall be labeled with the Threshold Limit and exposure time for the equipment it serves.

        Fire Extinguishers shall be placed inside the laser facility for the protection of the equipment and property.

        1. The most appropriate fire extinguishing agent, most likely Carbon Dioxide shall be used for this purpose.
          • Only fire extinguishing trained faculty, staff and students are permitted to operate a portable fire extinguisher as required by OSHA.
          • If an extinguisher or extinguisher training is needed for your facility, contact Environmental Health and Safety 542 - 8189.

        Laser Maintenance, Operation and Service

        Maintenance may not require beam access. Maintenance activity typically refers to cleaning and replenishment of expendables and is recommended by the manufacturers of the laser.

        1. Laser manufacturer specifications shall be immediately available to any authorized operator for health and safety reasons, as required by OSHA.

        Laser operation is directed by the manufacturer and shall be found in operating instructions given by the manufacturer.

        Service is understood to be a more involved process than is maintenance. It is done with less frequency, and it would be indicative of replacing the resonator mirrors and the repair of faulty components. Service is normally specified by the manufacturer and should be adhered to for health and safety reasons.

        Maintenance, Repair, and Service Personnel

        The LSO shall require that all maintenance, repair and service personnel to have the education, including health and safety, that is most appropriate for the class, type, and potential hazard of the laser or laser system being maintained, repaired, or serviced.

        General Public Laser Demonstrations

        When lasers or laser systems are used for artistic events, entertainment, or other laser related uses where the general public is in attendance, the following controls shall be utilized at Amherst College

        1. For outdoor artistic laser shows, the FAA shall be notified (FAA Order 7400.2)
        2. Only Class I lasers or laser systems can be used for general public demonstrations, displays, or entertainment in unsupervised areas without any additional requirements.
        3. For Class II and IIIa lasers or laser systems, unsupervised activities shall be limited to installations which prevent access to the direct or specularly reflected beams, or where the accessible radiation is maintained at the appropriate distance requirements.
        4. Class IIIb and IV lasers or laser systems shall only be permitted by the LSO, provided all the appropriate controls have been set into place for the protection of the general public under the following conditions
          • The laser operation must be under the control of a trained, authorized operator for the class and type of laser demonstration or display
          • When the laser is operated in an installation that is unsupervised, provided that the authorized, qualified person, who is present at all times, is responsible for the immediate deactivation of the laser system in the event of malfunction or other unsafe condition.
          • When all local, state, and federal requirements for safe and healthy operations have been met prior to the operation of the laser or laser system.
          • When the pre-show alignment and verification have been completed.
        5. Laser emission limitations
          • The general public shall not be exposed or have access to emissions of the laser radiation at wavelengths outside of the visible range (0.4μ-0.7μ) at levels exceeding the MPE.
        6. Optical laser radiation limitations
          • The general public shall not be exposed to laser radiation that exceeds the MPE levels during operation
          • Reflection from other surfaces and scattering material must be taken into consideration.
        7. Authorized operators and associated performers
          • All authorized operators, performers, and employees shall be able to perform their normal work activities without being adversely exposed to laser radiation levels in excess of the MPE.
        8. Scanning Devices
          • All devices, including rotating balls, used for display show shall be equipped with a means to prevent laser emission if the scanning device or associated equipment malfunctions.
        9. Laser operations - supervised
          • Laser demonstrations shall be conducted under the direction of an authorized operator who must maintain constant surveillance of the laser display, and terminate the laser emission in the event of equipment malfunction or other unsafe condition.
        10. The authorized operator shall be familiar with, and be able to see the entire area. If obstacles or other obstructions limit visual observation by the operator, then multiple observers shall be used. The observers must be able to communicate with the authorized operator.
        11. For these supervised installations, the laser radiation must not be limited by barriers, windows, or other applicable methods, so as not to exceed the MPE at any point unless
          • Laser radiation is to be maintained at a minimum distance of 3.0 meters above any surface upon which the general public would be able to stand or be elevated to during a performance.
          • The accessible laser radiation must be maintained at a minimum distance of 2.5 meters in lateral separation from any position where the general public is permitted to be during a performance or demonstration.

        Laser Education, Safety and Training

        It is the responsibility of Amherst College, under the direction of the Radiation Safety Committee and the Laser Safety Officer, to provide appropriate laser, laser system, and other applicable training to each person that will adjust, operate, maintain, repair, or service a laser.

        The level of training is dependent on the class and power of the laser

        Persons that are affected, but may not use the laser, laser systems, or other associated equipment must be trained at a level appropriate to their position.

        • This training will be for hazard recognition, as required by OSHA. Trainign of this type would apply, but is not limited to:
        1. Campus Police
        2. Custodial Staff
        3. Departmental Support Service Personnel

        Amherst College must establish and maintain a laser health and safety program that includes policies and procedures, training, and proof of adequate understanding of the training specific to the class and power of the laser.

        1. General contractors working for Amherst College that utilize lasers for alignment, leveling, and other applicable work shall insure that all persons working with or that are affected by the laser are appropriately trained. This includes signage recognition for the class of laser being use.
        2. Training is NOT required for Class I lasers.
        3. Any person who maintains, operates, repairs, or services a Class II, IIa, IIIa, IIIb or IV laser shall be trained to the appropriate level for the laser class, type, amount of use, and potential hazard.

        It shall be the responsibility of the Laser Safety Officer to determine the appropriate material, length of time, and any applicable internship before the potential laser operator becomes authorized.

        • Training, depending on the class, type, and potential hazard of the laser, is available in the following formats
          1.  Manufacturer's instructions or specifications
          2. Video Tapes
          3. Blackboard (on-line) Training
          4. Internship with a qualified, authorized operator, as permitted by the LSO The LSO shall be responsible for determining whether or not the potential user/operator has met the appropriate qualifications before permitting the person authorized status.

        In accordance with OSHA and other regulatory requirements, the LSO and Amherst College shall verify that the qualified, authorized person has met the applicable training criteria, and understands the material presented by completing a test or other evaluation. The test or evaluation will have both a test and a practical.

        Medical Surveillance

        Medical evaluation of potential laser operators* should be performed by a physician having knowledge of lasers and radiation. A physician having an occupational background would be appropriate for a medical evaluation of this type.

        Amherst College utilizes the services of

        1. Cooley Dickinson Hospital - Occupational Health

        Persons intent on using Class IIIb and IV lasers must first have the appropriate medical evaluation before becoming an authorized user. Medical evaluations, including eye exams, are NOT required for working with the following lasers

        1. Class I
        2. Class II and IIa
        3. Class IIIa

        Medical evaluations shall be required for persons working with the Class IIIb and IV lasers

        1. In accordance with ANSI standards and Best Management Practices, Amherst College shall include a thorough ophthalmologic and dermatologic examination for persons using Class IIIb and IV lasers.
        2. The authorized users of Class IIIb and IV lasers should be identified to Amherst College Human Resources by the LSO so that the appropriate medical evaluation, ophthalmologic, and/or dermatologic exam can be scheduled.
          • Included in the scheduling of medical evaluations shall be laser personnel-those persons that routinely work in the laser environment. These persons are most often full protected by engineering controls and administrative procedures.
          • The following are NOT required to be medically evaluated, even though they may be considered affected persons
        3. Incidental personnel-those persons whose work makes it possible (although unlikely) to be exposed to laser energy sufficient to damage their eyes and skin, persons using Class I, II, IIa, IIIa lasers

        Prior to Laser Use

        The primary reason for a prelaser operator examination is to determine a baseline health level for the potential laser operator. From the baseline, which is a measure of health and well-being, before work with lasers or laser systems is initiated, a physician (preferably occupational) can determine if any future adverse health (illness and/or injury) effects have occurred. These illnesses and injuries could include eye and /or skin abnormalities.

        Additionally, the pre-exam can identify whether or not a potential laser operator might be at risk, and not physically able to perform the assigned tasks or work activity.

        For laser class IIIb and IV laser operators, the following is required as part of the pre-examination:

        1. Medical History
        2. Visual Acuity Measurement, and
        3. any other examination as determined by the physician.


        Period examinations are not required.

        Incident examinations shall be performed by a physician having the appropriate knowledge for the work being performed. For eye injuries or exposures, an ophthalmologist or optometrist shall be consulted. For skin illness or injury, an occupational physician or physician having knowledge of laser or radiation exposure should be consulted.

        Termination examinations should be conducted by an occupational physician, ophthalmologist or optometrist as directed by the LSU and Human Resources.

        Medical Records

        Medical records, including examinations (prework, incident and termination) shall be maintained by the Amherst College office of Human Resources.

        Medical records shall be made available to the employee at anytime during normal business hours. If the medical records are requested by a physician or other applicable health care professional, the records can be provided with the express written consent of the employee.

        Waste Disposal

        All waste generated by the operator of lasers or laser systems shall be handled in accordance with Amherst College Policies and Procedures as directed by the EPA, NRC and Massachusetts Department of Environmental Protection (DEP). These wastes would include: dyes, flue and smoke filters, any solvents or other potentailly hazardous materials no longer usable.

        Click here to take the Laser Safety Assessment

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