The National Lightning Safety Institute (NLSI) recommends the suspension of outdoor activities when lightning is within a 6 mile range and further recommends remaining in shelter for 30 minutes after lightning has passed.
Lightning range can be detected via commercially available lightning detectors.
More often the “5 second rule” is used:
Sound travels 1 mile per 5 seconds.
To calculate lightning range divide the number of seconds counted from the time a lightning flash is seen by the naked eye until the time the associated thunder clap is heard by the number 5.
For example, if the difference between a visible lightning strike and the associated thunder is 15 seconds the lightning strike is approximately 3 miles away.
NLSI states that if you can see lightning and hear the associated thunder, lightning is within 6 to 8 miles, and lightning strikes can, indeed, occur 6 to 8 miles out from an electrical storm system.
It is Local 478’s policy that:
If lightning is seen and thunder heard all manned aerial lifts must be lowered to the ground and cease to operate. Unmanned lifts should be secured and all personnel are required to remain at a safe distance from the equipment.
If lightning is seen and thunder heard production must direct all but essential staff to shelter.
If lightning or related electrical storm activity is within a 6 to 8 mile range of production all outdoor activity must cease and employees must be sheltered until 30 minutes after the storm has passed.
For more information on workplace safety as pertains to lightning you may visit the National Lightning Safety Institute’s website at http://www.lightningsafety.com.