The Open Canopy Fatality and Risk Homeostasis Story
In 1999 I wrote a paper examining open canopy fatalities. Throughout the 1990’s the number of skydivers getting killed under fully open canopies was increasing every year. This was quite a cause of concern for USPA and parachute center operators. It was clear that part of the reason was the introduction and phenomenal popularity of parachutes made of zero porosity fabric. Ram air canopies made of ZP fabric are able to be pressurized at much greater levels than older canopies, make for a much more efficient airfoil. Aerodynamic efficiency translates in to higher speed and greater performance. Skydivers were exploiting those advantages very close to the ground with fatal results. In the past landing miscalculations might have resulted in a broken leg. With ZP canopies those same mistakes resulted in crippling injuries and deaths.
The question I originally addressed was “Why were skydivers taking such risks?” Were the increased fatalities a result of perception problems close to the ground? Was decision making errors the cause?
As I reviewed the fatality data and considered different possibilities I noticed that Cypres sales were increasing during the same time that open canopy fatalities were increasing, and remembered a grizzled old master rigger muttering, “Every time you make skydiving safer skydivers will figure out a way to make it dangerous again”. This was a very accurate restatement of the theory of risk homeostasis and seemed a likely avenue for investigation.
At the time SSK Industries was the only US distributor of Cypres units, and Cliff Schmucker very graciously shared sales and maintenance information. At that time Cypres had not yet introduced field replaceable cutters, so Cypres unit that fired had to be sent to SSK to be refitted. With data on sales and Cypres activation I was able to compare the increasing use of Cypres units, no pull/low pull fatalities that had been prevented, and open canopy fatalities.
I found that there was a strong correlation between Cypres saves and open canopy fatalities, as well as the increasing numbers of Cypres units in use and increasing open canopy fatalities. One of the graphs showed a spooky relationship in which Cypres saves one year were followed by an increase in open canopy fatalities the next, as if news of increasing safety was manifested a year later in more dangerous behaviors.
Correlation is not causation, but these results strongly supported the theory of risk homeostasis. I posted the paper on my website and it gained a fair amount of notice among skydivers and academics. In 2007 Casey Findley and Dr. Ron Self of Auburn University edited the paper and we presented it at the American Society of Business and Behavioral Sciences conference in Las Vegas.