Diving Safety
QUESTION: I was delighted to read your well-thought-out article on Diving Safety. I have been an active diver for longer than I care to remember and I also happened to work as safety professional before I retired. Since I retired I have done some volunteer work at the Naval Undersea Museum Library here in Keyport, Washington. While I was there I did a little study of SCUBA safety statistics and found the major concern was that the exposure time was unknown, and at that time no one seemed to want to even estimate it. So I found it surprising that you mentioned a death rate in you article (one death per 200,000 dives). If you have a reference for those figures I would appreciate your telling me what it is. I truly believe that the raw data DAN provides annually is not useful without knowing more about the time spent u/w. For example it is not significant to know that accidents have increased if the amount of diving increased proportionally during the same time period. In other words, knowing accident rates can help us identify and focus on true safety issues and accident trends. Thanks for your concern with safety. - Jim
ANSWER: I wrote that blog entry on scuba safety. Let me state right upfront, and maybe I should have made that clearer, that my thoughts were just that, thoughts on a topic based on what I believe in, what I've read and what I've seen. I DO have formal training in statistical analysis and actually did my doctoral thesis in part on the then-new use of computers for multivariate regression analysis and discriminant analysis and so on, but that was a long time ago.
As is, the figures I used in my statement, "Unfortunately, that number is uncomfortably close to the roughly 150 people who die every year in the US from/while diving. But what does this really mean? The rate is about five deaths per million dives. So the chance is one in every 200,000 dives." are gleaned from a variety of dive books I have read, some Google searches, and mostly from "Diving Science" by Michael Strauss and Igor Aksenov, both MDs. On page 185 they state" Deaths from SCUBA diving accidents have remained level at approximately 100 per year even though the number of SCUBA divers has increased 10-fold over the past three decades." (Also, on page 27 they state, "About one injury requiring medical attention occurs for every 1,000 SCUBA dives," and on page 32: "Two or three case of decompressions sickness occur for ever 10,000 SCUBA dives. (in the US).)
Now how did I get from that data to my statement? Like I said, I can not recall if I read it or computed it. I am certain, because I know how I write and think, that I did not simply guess or make it up. My likely thought process was this: "Diving Science" states that there are "an estimated 5 million certified SCUBA dives in the US..." I've read higher and much lower numbers, but let's assume it is 5 million. Let's say of those 5 million, half are somewhat active, and those half do an average of 12 dives a year, so that would be 30 million dives. If 150 people die from diving accidents, that would five deaths per million dives. If it's more like 100 deaths a year, then it'd be three deaths per million dives. If my assumption of half of all certified divers doing about a dozen dives a year is way off, then it is yet another number. If there are far fewer certified divers, the rate goes up, and so on.
I also have no doubt that a dive is not a dive is not a dive. In other words, yes, bottomtime makes a difference, as well as gender (according to "Diving Science" the vast majority of diving deaths are males), age (foolishness/invincibility in youth vs. declining health at age), equipment, training and so on. - Conrad H. Blickenstorfer