Diving Accident Investigation

Diving helmets waiting for accident investigations. Click for a larger image.

Compared to aircraft accident investigations, diving accident investigations are often ad hoc in nature, poorly conceived and poorly funded. Nevertheless, these investigations are just as important for the safety of the diving public as are similar investigations for the flying public. Unfortunately, no national regulations presently address how investigations of diving accidents should be conducted: volunteer investigators have no legal status for extracting information about an accident, and they have no legally binding protection from litigation based on the conduct of their investigation or on its results. That is, no business case can be made for conducting diving accident investigations, in spite of the moral authority for conducting them.

With the conviction that this untenable situation must eventually change, this presentation will describe one approach to diving accident investigations with particular emphasis on rebreathers and will draw some comparisons to aviation accident investigations by the National Transportation Safety Board (NTSB).

Aircraft accident investigations

The "black box" containing data recorded just prior to, and during, a commercial aircraft accident.

Pilots know that if they are involved in a fatal crash, the NTSB will investigate the accident by examining in excruciating detail everything those pilots did for hours, perhaps even days or weeks, leading up to that accident. It will investigate how often they called flight service to check on the weather. The NTSB will go through those pilots’ personal logbooks to check on their currency and proficiency, and it will check Federal Aviation Administration (FAA) records for a history of violations. NTSB investigators will also examine an aircraft’s logbooks to scrutinize its maintenance records. They will play back voice and radar data, and if a data recorder is available, they will analyze its contents.

Then they get personal. The NTSB and its FAA counterparts will talk to mechanics, surviving passengers, and friends to ask questions such as, “What were the aviators’ attitudes toward flying? Were they cavalier? Did they take unnecessary risks, or were they careful and methodical?”

Accidents happen.

Due to the detailed, scripted nature of NTSB procedures, the investigation may take up to a year to complete.

A few years ago a pilot’s engine failed and he was forced to make a water landing just off a beach. The ditching should have been survivable, but he lost consciousness on impact and sank with the airplane as it settled to the bottom in relatively shallow water. He drowned.

If he had been a diver, that would have been the end of the story. The public judgment would have been, “A diver drowned. He tried to breathe underwater; this is what happens.” But this victim happened to drown inside an airplane. So instead of the medical examiner simply saying that he drowned, the NTSB started its very thorough investigation procedures.

Fortunately, the pilot also had a surviving passenger. From the survivor’s statement, the aircraft’s maintenance records, and the mechanic’s testimony, an ugly story of reckless disregard for the most basic safety rules of flying began to emerge.

Do divers ever show a reckless disregard for basic safety rules? You bet. It’s unfortunate that the pilot died, but the events leading to his death were a useful reminder that the media in which we work and play, high-altitude air and water, are not forgiving. Humans are not designed for flying or diving, and nature only begrudgingly lets us trespass — on its terms.

The U.S. Navy and Coast Guard are chartered to investigate diving accidents. Unfortunately, there is a huge discrepancy in the number of personnel and the amount of funding for aviation accident investigations compared to diving accident investigations. The NTSB has hundreds of personnel and tens of millions in funding available, whereas the entire U.S. Navy has at most a handful of investigators with no investigation-specific funding.

Investigation team requirements

In the best of all worlds, an investigation team should have access to both a manned and an unmanned test facility, access to experts in all diving equipment (scuba, rebreathers, helmets), and the ability to conduct and interpret gas analyses — sometimes from minuscule amounts of remaining gas. At a minimum, such a team needs the ability to download and interpret dive computer/recorder data. Some investigations may require the simulation of UBA-human interactions for “re-enactment” purposes. An investigation team should also have diving medical expertise available to review medical examiner reports for consistency with known or discovered facts regarding the accident. Last, it should have in-depth knowledge of police investigative procedures, particularly of the procedures and documentation for maintaining “chain of custody”.

Do rebreather investigations have a future?

Considering the resources and time-frames required for laboratories such as the Navy Experimental Diving Unit (NEDU) to conduct diving equipment evaluations on a limited set of accident cases, and the unfunded costs associated with those investigations, it is difficult to imagine a resolution to an ever-increasing need for rebreather investigations. Almost certainly, no independent federal agency similar to the NTSB will ever be responsible for investigating diving accidents, simply because diving accidents lack national attention: the public at large is not being placed in jeopardy.

It is also unlikely that diving equipment manufacturers would welcome federal agency oversight and regulations comparable to those engendered by the FAA and NTSB. Diving might become exorbitantly expensive. For instance, if a $5 part available for purchase in an automotive store were to be used in an aircraft, it would become a $50–$500 part because of FAA required  documentation that it meets airworthiness standards.

The U.S. Coast Guard initiates diving accident investigations and in some cases conducts hearings into those accidents; however, with its enhanced role in Homeland Security, the Coast Guard is unlikely to welcome any efforts to diversify its mission. The cost/benefit ratio would appear to be too great.

For the future, as Dick Vann of DAN has suggested, the resolution may ultimately depend on rebreather users funding a team of dedicated, professional accident investigators. The cost of conducting worthwhile investigations has yet to be determined, and therefore the amount of funding needed to support it is unknown. I suggest that obtaining those estimates should be a priority as we, rebreather users and the industry, decide the next steps in investigating rebreather accidents.


The above are highlights from this author’s publication of the same name, found in: Vann RD, Mitchell SJ, Denoble PJ, Anthony TG, eds. Technical Diving Conference, Proceedings. Durham, NC: Divers Alert Network; 2009; 394 pages. ISBN# 978-1-930536-53-1.

This book is available for download at no cost as a PDF file from the Divers Alert Network website (http://www.DiversAlertNetwork.org/or from http://archive.rubicon-foundation.org/8300

A Frog Drowned in My Pool

Leopard Frog (Rana pipiens). Photo credit: Bill Sutton

The little fellow was fast, and wily.

I was chasing him around the pool with a skimmer net, trying to herd him to the side of the pool where I had some chance of scooping him up with my hands. As the net approached he would kick to the eight foot deep bottom and then gracefully glide, legs in trail, along the contour of the bottom and sidewalls up to the edge of the pool. In dark water that tactic worked beautifully because his enemies could not see where he was going. But since he was in clear pool water I could see exactly where he was headed.

I’d sneak around the pool edge, out of his sight, and then grab for him as he floated at the surface. But he’d invariably see me in time to flip over and kick to the bottom again.

I had to admire his strength, speed and agility. He was clearly in his element. And besides that, he could breathe through his skin, absorbing oxygen from the water. Neat trick I thought, as I remembered various attempts by engineers to create artificial gills for humans — attempts that have all failed — so far.

Tadpoles have gills, but those gills are lost as the tadpoles metamorphose into frogs. Instead, frogs use a combination of lung breathing and skin breathing, called cutaneous respiration. Breathing through their skin allows them to remain underwater for months during the winter, when they are hibernating. However, when frogs are actively swimming, their oxygen demands are quite high, as you would expect. As the chase continued I had no idea how much or how little oxygen he could extract from the pool water.

For cutaneous respiration to work, frog skin has to stay moist, hence their desire to be close to water. But this frog was in the wrong water. I was about to pour chlorine into the pool, and if he didn’t get out of the pool, he wouldn’t survive. The chase was really in his best interest, but he didn’t know that of course; he was simply trying to avoid becoming my lunch.

So basically he never had time to take a breather. I figured at some point he’d grow tired from all the exercise and would allow me to catch him in the net and lift him out of the pool.

I was wrong. Before he quit swimming he apparently ran out of oxygen, in spite of the fact that he was getting oxygen from the water through his skin. But he wasn’t getting enough; he passed out.

Well, that sure made it easy to scoop him up.

Once I got him in my hands, I started frog CPR. No, I did not give him mouth to mouth ventilation. But I did give his little chest tiny squeezes, thinking that would do him some good. Apparently it didn’t; he never regained consciousness.

I buried him in my garden with all the solemnity due a frog, and vowed over his little green body that I’d do better with keeping the chlorine levels up so future frogs would not be attracted to the pool. Of course that was for my benefit as well, because where frogs are, water moccasins are not far behind.

I think it’s tough being a frog.

I mostly kept to my promise, but inevitably, another leopard frog or two attempted to take up residence in my concrete lined pond.

Being a scientist, I decided to conduct an experiment. I repeated my earlier, potentially deadly chases, but this time I reacted instantly when the frogs passed out. Soon as they went limp I scooped them up with my net and laid them in the grass. Before long they recovered and started frog-hopping away. Speed was of the essence in their rescue, and quick reactions on my part worked to keep the frogs alive.

So yes, frogs can breathe through their skin, absorbing oxygen and releasing carbon dioxide, but only enough to support resting needs. When they are active, they must supplement gas exchange by gulping air into their lungs. Now I know.

(The loss of the first frog was an accident, not animal cruelty! Do not repeat this in the name of science, because it also is not science.)

I’ve since learned that I’m not the only person with frog-in-pool problems, and conveniently, small animal escape devices are available. Here’s a video of one that allows frogs to self-rescue without being dependent on any near-death escapes foisted upon them by me. (I’m not associated with the manufacturers or dealers in any way.)