Have you ever wondered what happens when a severe storm comes in while you are diving? Ideally, this will never happen to you, because you do due diligence when it comes to the weather and safe diving. But, what if you are boat diving when one of those wild squalls rolls in and there is lightening? I was watching the weather on the news last night and wondered about lightning strikes when diving. I decided to do a little research and blog about lightening and the boat diver.
During research today I read an old article about a boat diver in Florida who died after lightning struck his scuba tank. Instructors briefly go over weather and boat diving in Open Water Certification classes, to the degree that you should stay in when it storms. So we all know the drill, but I guess this guy went boat diving despite a severe thunderstorm warning. In any case, he paid the ultimate price for being on the water during a storm. The short version of the story goes like this: The diver resurfaced during a boat dive to exit the water. The boat was 30 or so feet away from the diver. While waiting for the boat to swing around, a bolt of lightning struck the diver’s tank and knocked him unconscious. He died from electrocution before ever seeing the shore.
According to an article in Undercurrent.org, 2007, statistics show that approximately 75% of USA fatalities by lightning strike occur in the open or under a tree. While another 12% or so take place near or in the water, while boating or fishing. It would follow that divers would also run a relatively high risk of lightning strike while on the surface of the water. I finished the article determined to write a blog on the issue today, because death by lightning is certainly a potential risk for every diver.
Because of the mechanism of action of lightning, it rarely strikes the surface of the ocean. This is good news. The bad news is water is highly conductive, and the degree of conductivity is proportional to salinity. I remember this from science class. Because water conducts electricity so well, and the ocean has a high salinity, one would assume when lightning strikes the water it would be carried for some distance? And, if you are in or under the water during a strike, you will be electrocuted?
To answer this question I went to review the properties of water and this is what I found:
- Rain water is essentially distilled water and conductivity equals zero. And, water from runoff, being for the most part rain water, is a very poor conductor of electricity.
- Spring water is slightly more conductive than rain water due to the presence of minerals. Conductivity will vary according to mineral content of the spring water.
- Ocean Spray has some salinity. The information I read reinforces my memory, Salt (NaCl) does increase the conductivity of water. Coastal waters and coastal air contain salt, thus spray is somewhat more conductive than spring water.
- Water in areas where fresh water contains some salt are more conductive than ocean spray. The level of salinity of these areas varies with the tides. When the tide flows in, or is high, the salinity tends to increase. With outflowing tides the salinity decreases. These areas are more conductive than ocean spray.
- Evaporation increases salinity by raising the salt to water ratio. Loss of fresh water will increase the salinity of the water, thereby increasing the conductivity of the water.
- Temperature also determines conductivity. Heat excites atoms and molecules, which increases conductivity. The surface of the ocean tends to have higher concentrations of salt due to evaporation, and warmer temperatures due to the warmth from sunlight, so conductivity is slightly higher at the surface of the ocean.
- Pressure (depth) itself doesn’t really have much effect on conductivity.
- Distance works in your favor. As you move away from the lightning strike on the ocean (which is rare) or a strike on an object on the ocean surface (much less rare), conductivity decreases.
What is the bottom line? Although lightning rarely strikes the surface of the ocean, it is drawn to objects floating in the ocean. You, your boat, your dive buddies, and flotsam, are all lightning rods. If something or someone floating in the water close to you receives a lightning strike, you will likely get zapped. Even if you are not fatally electrocuted, you could suffer electrical burns, organ injury, and/or cardiac arrest. And, your dive buddy who was struck is likely a fatality.
What should you do if you find yourself caught on the surface in a lightning storm? Get out of the water, onto the boat, and out of your gear as quickly as possible. Then follow the instructions of the boat ops crew until they get you safely to shore. They will likely instruct you to stay towards the middle of the boat, and under cover if possible. Stay away from metal and electrical equipment. If the boat has antennas or a lightning rod of some sort, stay away and do not touch it.
Be your own safety advocate. Check the weather before any kind of diving. Don’t depend on the Dive Guide, boat operator, Instructor, or other dive leader to know the weather forecast. If the forecast is for thunderstorms, don’t go near the water. If you are on the water when a storm appears in the distance, return to shore long before the storm arrives. Stay out of the water, off the dock, and indoors during severe weather. Safety first! Now we know what happens when lightning strikes when you are diving.
Authored by Lisa J Henry
“Be the sea”