A safe distance from lightning

You said that the bolt of lightning occurs thirty seconds before one hears the sound. I heard that if you count five seconds after seeing the lightning it is five miles away. I don't remember ever hearing thunder after thirty seconds. It seems to me the sound would have diminished so as to not be audible after that time. Please check on this. Are pool personnel aware of this requirement (clearing swimmers from the pool)?  Ethel, Santa Fe, New Mexico

I said, in the Lightning Strikes Indoor Pools article:

If the "Flash-To-Bang" delay (length of time in seconds between a lightning flash and its subsequent thunder) is 30 seconds [not 5], the lightning is five miles away.

You can probably hear thunder up to 15 miles away, but rarely beyond 15 miles (about 75 seconds flash-to-bang delay), because the sound bends upward and misses you. Also thunderstorms are chaotic maelstroms that disorganize and dissipate sound waves before the thunder sound can reach you from that far away.

But back to the 30 second warning. If the time is 30 seconds or less between seeing the flash to hearing the bang, you are too close, and need to find shelter. Lightning can leap and strike two to three miles from its last strike. So five miles may place you fairly close to the next strike.   Yes, lifeguards are aware of the requirement. They do clear the pool.

Further Reading

Kaleidoscope Sky by Tim Herd

(Answered , 2008)

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