UVM Tower The University of Vermont date
  A Publication of UVM Extension's Vermont Vegetable and Berry Program

Lightning Safety

by Vern Grubinger
Vegetable and Berry Specialist

A recent tragedy in my state serves as a reminder of the dangers of lightning. A teenager was hit by a ‘bolt from the blue’ during his first week of work on a vegetable farm. The owners have asked me to spread the word about lightning safety, in the hope that something positive can come from this terrible occurrence.

The challenge to farmers is that agricultural work must be done during a variety of weather conditions. Farm work doesn’t stop just because the weather forecast calls for rain or thunderstorms. The key to keeping your family, employees,  visitors (and yourself!) safe is knowing when to interrupt or cancel farm activities and having a plan to protect people from injury or death when thunderstorms threaten.

There are millions of lightning strikes every year, and though the odds of getting hit are low, they are high enough that the risk must be taken seriously. Lightning is more deadly than hurricanes or tornadoes, killing an average of 73 people and injuring 300 others annually in the United States.

The National Oceanic and Atmospheric Administration (NOAA), home to the National Weather Service, provides a lot of following information about the nature of lightning and how to avoid its perils. Some of the following is adapted from their web site http://www.lightningsafety.noaa.gov/.

Lightning is a gigantic electrostatic discharge--the same kind of electricity that can shock you when you touch a doorknob--between a cloud and the ground, other clouds, or within a cloud. It is caused by the attraction between positive and negative charges in the atmosphere, resulting in the buildup and release of electrical energy. This is associated with rapid heating and cooling of the air which produces a shock wave that creates thunder.

Thunder is the sound made by a flash of lightning. As lightning passes through the air, it heats the air quickly, causing it to expand rapidly and create a sound wave. That sound, thunder, travels about a mile every 5 seconds. If you count the seconds between the flash of lightning and the crack of thunder and divide by 5, you get the number of miles away from you, so 10 seconds is 2 miles. Normally, you can hear thunder about 10 miles from a lightning strike. Since lightning can strike outward 10 miles from a thunderstorm, if you hear thunder, you are likely within striking distance of the storm.

While many lightning casualties happen at the beginning of an approaching storm, more than half of all lightning deaths occur after a thunderstorm has passed. The lightning threat diminishes after the last sound of thunder, but may persist for more than 30 minutes. When thunderstorms are in the area, but not overhead, a lightning threat can exist even when skies are clear. If you can see lightning or hear thunder, the risk is present. Louder or more frequent thunder means lightning activity is approaching, increasing the risk. Coordinators of outdoor events, including farmers and their crew leaders, should monitor the weather and know when to evacuate workers to safety, erring on the side of caution.

There is no safe place outside when thunderstorms are in the area! If you hear thunder, you are likely within striking distance of the storm. Adhere to the slogan: When Thunder Roars, Go Indoors! Too many people wait far too long to get to a safe place when thunderstorms approach. Unfortunately, these delayed actions lead to many of the lightning deaths and injuries in the U.S.

Some safety organizations promote the “30-30 rule.” If the time delay between seeing the flash of lightning and hearing the bang of thunder is less than 30 seconds, you should already be moving toward shelter. To be safe, outdoor activities should cease a half hour before and after a thunderstorm, since lightning can strike 30 minutes before or after a visible storm.

Have a lightning safety policy for your farm, and make sure all employees understand it. This should include: canceling or postponing outdoor activities early if thunderstorms are expected; making sure that crew leaders or other supervisors know they must stop work if the weather becomes threatening; making sure crew leaders pay attention to early signs of thunderstorms such as high winds or dark clouds and do not start any new task that cannot be stopped quickly; making sure that crew leaders can communicate quickly with all workers, regardless of their location on the farm, using radio or other devices; making sure that everyone working outside or in unsafe structures such as greenhouses has the ability to get to a safe place quickly. Everyone on your farm should know the procedure for contacting emergency services if cell phones are not available, or lack reception.

Relatively safe places during a thunderstorm are substantial buildings and fully-enclosed, metal-topped vehicles. A substantial building is one that is fully enclosed with a roof, walls and floor, and has plumbing or wiring that provides grounding. Once inside, stay away from showers, sinks, bath tubs, and electronic equipment such as stoves, radios, corded telephones and computers. Less safe buildings include car ports, open garages, picnic shelters, pavilions, tents of any kinds, and sheds. Hoop houses and greenhouses with significant ground contact through ground posts or dedicated grounding or lightning protection systems are safe. Finding cover is important and being under a structure is better than being in the open.

Fully enclosed metal-topped vehicles include cars, vans, buses, trucks, or tractors with an enclosed cab. Unsafe vehicles include golf carts, convertibles, or any open cab vehicle. While inside a safe vehicle, do not use electronic devices such as radio communications during a thunderstorm, and keep windows closed. If you drive into a thunderstorm, slow down and use extra caution. If possible, pull off the road into a safe area. Do not exit the vehicle during a thunderstorm.

If someone is struck by lightning, get immediate medical attention. Lightning victims do not carry an electrical charge and are safe to touch. Call 911 and monitor the victim. They may need CPR or an automated external defibrillator; is your farm prepared to provide either of these?

For more information see OSHA's publication: Lightning Safety When Working Outdoors

Published: July 2012. Revised July 2021.
Return to Vermont Vegetable and Berry Grower Pages