Environmental Health & Safety

Lightning Plan

June 2012

Emergency - Call Amherst College Police 

(413) 542-2111 

(Ambulance, Fire, Haz-Mat, Police)






According to the National Lightning Safety Institute (NLSI) the following procedure should be used to determine when a swimming pool should be evacuated during thunderstorms and lightning strikes. The NLSI recommends this conservative attitude because lightning's behavior is random and unpredictable.

1st: Designate a Weather Safety Person

This person should watch the weather and monitor a weather station (radio or television) to obtain a reputable, localized weather report.

2nd: Use a "Flash to Bang" method to determine rough distance and speed

The "F-B" method gives a distance (in miles) as to how far the storm is.

To perform this procedure:

  • Watch for a lightning strike and count the number of seconds (one-one thousand, two-one thousand etc.) before the thunder. For every (5) seconds of F-B the lightning is approximately one (1) mile away.
  • F-B range of 10 seconds = 2 miles
  • F-B range of 15 seconds = 3 miles
  • F-B range of 20 seconds = 4 miles
  • F-B range of 30 seconds = 6 miles

3rd: At a F-B count of 30 (6 miles) the swimming pool should be evacuated, and should not be re-entered until 30 minutes after last thunder

This procedure applies to both indoor and outdoor swimming pools, which are connected to much larger surface area of underground water pipes, gas lines, electric and telephone wiring. Lightning strikes to ground anywhere and can utilize this system of metal, causing shocks elsewhere, including pools.

If you have comments, concerns or questions contact Environmental Health & Safety at (413) 542-8189, or the National Lightning Safety Institute at http://www.lightningsafety.com/