From RISKS 25.57.
I have friends who dive and hope to get certified myself soon so this is of particular concern.
Date: 17 Feb 2003 05:35:20 -0800 From: tom.race@skipton.co.uk (Tom Race) Subject: Scuba diving computer recall
[See also Risks in scuba equipment, Carl Page, RISKS-21.41]
In simple terms, a dive computer monitors the amount of nitrogen dissolved in the diver’s blood. Typically worn like a wrist watch, it tracks the diver’s depth and calculates the absorbed nitrogen according to a mathematical model of the human body’s various tissues.
If a diver surfaces too quickly with too much nitrogen in the body it is released as bubbles within the blood or tissues, potentially causing injury or death through Decompression Sickness (DCS). Divers typically rely heavily on a computer to tell them when to surface to avoid DCS.
The manufacturer below is being sued over the mathematical model, which has a faulty assumption, or more likely a complete oversight. The model embedded in this computer assumes that the diver on the surface continues to breath whatever gas mixture they were diving with. When the diver is using nitrox, a gas mixture containing extra oxygen and therefore less nitrogen than air, the computer will assume that they are releasing nitrogen at a higher rate than reality. Over several dives and several intervals on the surface, the state of the mathematical model and the diver’s actual nitrogen levels may become seriously different, and in the ‘wrong’ (more risky) direction.
A failure of requirements specification or code inspection? The lawsuit refers to a ‘manufacturing defect’.
I have an interest, since I have a nitrox computer from the same manufacturer. Fortunately mine is more recent, and I have not used it for gases other than air.
Tom Race
- - - - - - - - - - - - Uwatec, Scuba Pro and Johnson Outdoors Subject of Class Action Seeking Product Recall; 5 Feb 2003 Dive industry leaders Uwatec and Scuba Pro, and their parent company, outdoor equipment conglomerate Johnson Outdoors, Inc., have been sued in federal court by a former authorized reseller, Robert Raimo, seeking a mandatory recall of all Aladin Air X Nitrox dive computers manufactured before 1 Feb 1996. The suit seeks certification as a class action on behalf of all owners of the dive computers, and all persons who acted as retailers, dealers, wholesalers or distributors of the dive computers. The suit claims that 1995 model Aladin Air X Nitrox dive computers have a manufacturing defect that prevents the computer from switching from underwater to surface, or air mode when the user returns to the surface. As a result, the computer continues to calculate a diver’s decompression obligations as if the diver were breathing enriched air, or nitrox, containing as little as 50% nitrogen, while on the surface, instead of properly calculating the diver’s decompression obligations and off-gassing while the diver is breathing air, which contains 78% nitrogen. This defect causes the computer to underestimate residual nitrogen loads, and to overestimate the diver’s safe repetitive bottom times, thereby significantly increasing the diver’s risk of contracting decompression sickness (bends). The suit alleges that the defect is likely to affect experienced divers making multiple nitrox dives in a single day to maximize bottom time, such as those conducted on increasingly popular “live-aboard” dive vacations in exotic locations, far away from the nearest treatment centers capable of saving the life of a diver stricken with decompression sickness. The so-called “air-switching defect” was first described in an internal Uwatec memo dated 30 Jan 1996, which warned one of the company’s test divers about “the faulty Aladin Nitrox”. The memo described how to manually override the defect so the diver could safely use his computer until it was replaced by Uwatec. After this memo was sent to Uwatec’s U.S. management, they drafted a product recall notice. However, the suit alleges the managers were fired before they could issue the recall notice, and the defendants have maintained a “conspiracy of silence” ever since. Copies of the 1996 memo and recall notice are attached as exhibits to the complaint and may be viewed on the News section of the Web site of Raimo’s attorney, David Concannon, at www.davidconcannon.com. Raimo was stricken with Type II decompression sickness after using a 1995 model Aladin Air X Nitrox on four nitrox dives off Bonaire in Apr 2002. He is the former owner of two retail dive centers in New York. According to Concannon, the suit was filed as a class action only after Johnson, Scuba Pro and Uwatec rebuffed Raimo’s requests that the companies issue a voluntary recall. The suit was filed in Oakland, California because four other lawsuits filed by divers alleging they were injured by the same model computer are currently pending there and are scheduled for trial in Nov 2003.