Lightning and the Outdoor Crew
Why this matters
Lightning kills about 20 people a year in the United States in recent years, by National Weather Service counts, and injures many more, most of whom survive with lasting nerve, hearing or memory damage. Roofers, landscapers, pool techs and anyone working a yard or a ladder are in exactly the places and postures that put a person in the path. The rule that prevents nearly all of it, repeated in the OSHA and NOAA fact sheet for outdoor workers, costs a crew about half an hour: when you hear thunder, go indoors, and stay there for thirty minutes after the last thunder. The failure is waiting for the rain, the dark cloud or the first flash overhead, because by then the risk has already been present for some time.
The shop's stop-work procedure, including who calls it and when work restarts, is its own document. See related: The Lightning Stop Work SOP. This card explains why the rule is built the way it is.
Why "when thunder roars, go indoors" replaced the older rule
Sound travels roughly one mile every five seconds, so counting the seconds from a flash to its thunder gives the distance. The older "30-30 rule" told people to take shelter when that count fell to 30 seconds, about six miles. The National Weather Service dropped that first half because lightning routinely strikes well beyond six miles from the storm, sometimes from a clear patch of sky ahead of it, and because counting delayed people while the storm closed in. The current message is simpler and safer: thunder is audible out to roughly ten miles, and lightning can reach about that far, so if you can hear thunder, you are within striking distance. The count still has one use, telling you how fast the storm is closing, but it no longer tells you whether to move.
Why the second thirty minutes exist
The trailing edge of a storm is as dangerous as its leading edge. The rain stops, the sky lightens, people go back out, and the storm's back side is still producing strikes miles behind the rain. That is the reason for the thirty-minute wait after the last thunder, not after the last rain or the last visible flash. Every new rumble restarts the clock. On a day with storms training through, the clock can reset several times, and that is the rule working, not failing.
How a strike reaches a person
Few lightning casualties come from a direct strike. The current spreads, jumps and travels along conductors, which is why being near the strike point is enough.
HOW CURRENT REACHES A CREW MEMBER
direct strike side flash ground current
| | |
v [ tall tree ] strike point
person | \ |
| \-> person ~~~~~+~~~~~
| nearby current runs out
through the soil;
two feet apart =
a voltage across
the legs
conduction upward streamer
strike on fence, gutter, a person under a
pipe, wiring -> current runs charged cloud sends
along metal to whoever is up a streamer that
touching it, inside or out joins the strike
Ground current causes more casualties than any other route, according to the National Weather Service, and it is why a whole crew can be injured by one strike in a yard. Side flash is why sheltering under a tree is one of the worst things to do. Conduction is why "inside" is not automatically safe for a tech who is touching the service, a panel or metal piping.
Why roofs, ladders and open yards are the worst places
A roof puts you at the top of the lot. Lightning favors the tallest, most isolated object in the area, and on most residential lots a person on a ridge is close to it. The roof also gives no shelter, and the crew's way down is a ladder that takes time, often with wet hands and a slick surface, which is how a lightning stop turns into a fall. The decision to come down has to be made earlier on a roof than anywhere else, because getting off takes the longest.
A ladder is height and an exposed posture. Metal does not attract lightning; this is a common myth. What makes a ladder dangerous is height, isolation and the fact that the person is standing on it in the open. A fiberglass ladder does not make anyone safer from lightning.
An open yard, a field or a pool deck makes you the tallest thing nearby, and a pool or wet ground adds a path for ground current. A pool tech at the water's edge is in one of the more exposed positions in residential service.
A tree is worse than open ground, because it invites the strike and then side-flashes to whoever is beside it. An open-sided shed, a carport, a porch, a gazebo or a pole barn without wiring and plumbing does not protect either; the National Weather Service lists these small and open structures as unsafe.
What actually counts as shelter
Two things count. A substantial enclosed building with wiring and plumbing, because the building's conductors carry the current around and into the ground rather than through the people inside. And a hard-topped, fully enclosed metal vehicle with the windows up, because the metal shell carries the current around the occupants. It is the shell, not the tires, that protects. A truck with a hard cab qualifies; an open cab, a convertible, a mower, a golf cart or a utility vehicle with a fabric top does not.
Inside, three behaviors still matter: stay off corded phones, away from plumbing fixtures and water, and away from wired equipment and the electrical service. For a tech working on a panel, a service entrance, an outdoor disconnect or metal piping that runs outside, a storm overhead is a conduction risk even while standing indoors. Stop that work, close up, and step away until the clock clears.
Worked example: a roofing crew and a storm that arrives fast
A three-person crew is shingling a two-story house in July. Two are on the roof, one is cutting at the ground. A storm was forecast for late afternoon.
2:10 p.m. The ground man sees a flash to the west and counts 40 seconds to the thunder. At five seconds a mile that is 8 miles. He calls it immediately, which is correct: thunder was heard, so the crew is within striking distance whatever the count says.
Why the count still mattered. Thunderstorms commonly move at 10 to 25 miles an hour. At 20 miles an hour, a storm 8 miles out reaches the house in about 24 minutes (8 divided by 20 is 0.4 of an hour). Getting off this roof takes time: tarping the open section, lowering tools, and two people descending a ladder one at a time took the crew about 12 minutes on a dry day. That leaves a margin of roughly 12 minutes on the storm's arrival, and no margin at all on the risk, which started at 2:10. Had they waited for the first raindrops, they would have been on the ladder with wet rungs and the storm already overhead.
2:22 p.m. All three are in the truck cab, windows up. The open roof section is tarped. Nobody sits in the open-sided garage, which would have felt like shelter and is not.
The clock. Thunder continues. The crew notes each rumble: the last ones come at 2:31, 2:44 and 3:02. Each one restarts the thirty minutes, so the earliest return is 3:32, which is 30 minutes after 3:02. At 3:15 the rain stops and the sky to the west brightens; one crew member wants to go back up. That is the trailing-edge trap, and the clock says no.
3:32 p.m. No thunder since 3:02. Before anyone climbs, the lead checks the roof surface and ladder footing, which are wet; the crew waits until the shingles dry enough to walk, and works the ground tasks first.
What would have changed the call. If the storm had been forecast to build directly overhead, as afternoon storms often do in humid weather, there would have been no flash-to-bang warning at all, and the first thunder could have come from a few miles away. On such days the right move is to plan the work so the roof is closed up and the crew is off before the forecast window opens. And if the nearest shelter had been a long walk away, as on a large rural property, the time to get to it would have had to be added to the time to get off the roof. That is a planning question for the morning, not the moment.
Myths that get people hurt
- "Rubber boots or tires protect you." They do not; a strike has crossed miles of air and a few millimeters of rubber mean nothing to it.
- "Lightning never strikes the same place twice." Tall structures are struck repeatedly.
- "If it is not raining, it is safe." Strikes routinely land outside the rain.
- "Crouching makes you safe." The lightning crouch is a last resort for someone caught with no shelter at all, and it only slightly reduces risk. If a crew is caught in the open, spread out so one strike cannot injure everyone, and get to shelter as soon as possible.
If someone is struck
A person struck by lightning carries no electrical charge and is safe to touch immediately. Call 911. Lightning often stops the heart and breathing, and the injured can recover if CPR starts quickly, so start CPR on anyone not breathing normally and use an AED if one is available. When several people are struck, treat first those who appear lifeless, because people who are breathing and moving are likely to survive without immediate help, the reverse of ordinary triage. Move the victim and the rescuers to shelter if the storm is still active and it can be done quickly, because the rescuers are still under the storm. Anyone struck needs medical evaluation even if they feel fine, because burns, eye and ear damage and heart rhythm problems may not show at first.
References
- National Weather Service, Lightning Safety program (when thunder roars, go indoors; 30-minute rule; how lightning injures; safe shelter)
- OSHA and NOAA, Lightning Safety When Working Outdoors fact sheet
- American Heart Association guidance on CPR and AED use
- See related: The Lightning Stop Work SOP