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January 2009    Download the Entire Issue (PDF) Available to the Public Vol. 24, No. 1   RSS Feed for Undercurrent Issues
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When Bad Air is Pumped into Your Tank

a recent study states it happens more often than you think

from the January, 2009 issue of Undercurrent   Subscribe Now

The risk of getting bad air is low, but it exists and can be fatal. One still finds occasional cases of faulty air compressors that suck in contaminants like engine exhaust, paint fumes and solvent vapors, resulting in a lethal mix. That’s what happened aboard the Maldives liveaboard Baani Adventurer last May. A Russian diver died, two dive instructors were hospitalized and eight other divers had to be treated for carbon monoxide poisoning in their tanks. The police investigation found that a crack in the air pipe leading to the boat’s Bauer compressor was poorly mended with duct tape, allowing contamination in the form of engine exhaust to enter (read the details in our July 2008 article “The Baani Adventurer’s Lethal Air Compressor” online at Undercurrent).

After a chance meeting on a dive trip, Ian Millar, director of hyperbaric medicine at the Alfred Hospital in Melbourne, and Peter Mouldey, M.D., of Southdown Medical Centre in Mississauga, Canada, agreed there was a widespread lack of knowledge about the potential of contamination within the compression process, and the limitations and failure risks of commonly used filtration systems. There’s little evidence of a widespread problem related to compressor production of carbon monoxide or volatile hydrocarbons. However, after studying unrecognized, unreported deaths by compressed-air contamination, Millar and Mouldey believe that the dive industry could be missing a wider problem, and that there’s a higher potential for these types of fatalities than previously thought.

There’s the cave-diving incident in Florida, a near-miss due to toluene contamination, with the diver initially becoming disoriented and swimming in an agitated fashion before becoming lethargic and requiring a rescue. Then there’s a case involving an air compressor at a Canadian fire department station, which often produced carbon monoxide. The contamination disappeared after a full overhaul and filter change, only to recur shortly afterwards. It appears to have been due to a poor installation location that allowed hot exhaust air to recirculate, resulting in compressor overheating, with consequent oil breakdown contaminating the breathing air.

Even Low Levels of CO Can Kill Divers

After diving deaths, air is often untested or insufficiently tested with techniques that would detect low levels of carbon monoxide or volatile hydrocarbons. This is important, because levels that don’t cause loss of consciousness may still pre-dispose the diver to cardiac arrhythmia or underwater impairment of judgment that can lead to fatal error.

In the Divers Alert Network (DAN) data of diver fatalities between 1995 and 2000, 145 fatalities were recorded as a result of drowning or near-drowning, with the initial injury or problem labeled as “unknown.” It seems reasonable to speculate that gas contamination may have contributed to some of these deaths. A DAN review of 451 fatalities over a five-year period suggests that only 15 percent of the divers had a carboxyhaemoglobin (COHb) measurement (the amount of the body’s hemoglobin mixed with carbon monoxide instead of oxygen) taken at the time of death. Of those sampled, 3 percent had a fatal concentration of COHb at the time of measurement.

In 2006, the United Kingdom’s Health and Safety Executive reported on an examination of diving equipment implicated in 54 accidents and incidents of all types. While only five involved a suspected “bad fill,” 41 of the 54 tested air samples failed the moisture content standard. The Swedish Consumer Agency sampled air from nine dive suppliers in 1996, finding one case of oil contamination. In 2007, five of 20 failed, two due to excess carbon dioxide and three due to moisture. In parts of the U.S. where lab analysis of the air is required rather than simple detector tube sampling, rates of failure to meet acceptable carbon-monoxide levels have been as high as 3 percent in recreational dive air (10 parts per million is the limit). The U.S. Navy has encountered similar problems at a frequency of 2.5 percent using a carbon-monoxide specification of 20 parts per million.

While this doesn’t confirm there is a specific problem with volatile hydrocarbon contamination produced within compressors, it does suggest there is probably a systematic deficiency in the quality and performance of compressor installations.

What About Nitrox?

With the rapid increase in the use of Nitrox, there are many instances of conventional air compressors being used with oxygen- enrichment systems feeding the intake to provide Nitrox fills. Makeshift arrangements are of concern with respect to the risk of fire as well as contamination of breathing air. The increased oxygen concentration passing through Nitrox compressors degrades the compressor oil more rapidly than normal, which may generate toxic byproducts, shorten the compressor and filter life, and increase the risk of contaminated breathing air.

High-quality synthetic oils should, in theory, be less susceptible to thermal and oxidative degradation than mineral oils. Even so, evolving recommendations suggest oil changes may be needed after only 25 percent of the time usually allowed.

How Divers Can Ensure a Clean Tank

Millar and Mouldey believe it’s clear that air quality is an important issue that has been inadequately addressed. They suggest divers ask questions, look for certificates of compliance with appropriate standards or codes of practice, and investigate standards of air-quality control at dive destinations, before traveling there if possible. Particular caution should be applied for hot, humid locations, especially if compressors are installed near walls in small rooms, or if they’re run in the heat of the day.

The most sensitive analytic method for hydrocarbons is to get into the habit of smelling tank air well before you dive. If you don’t have a clear nose and intact sense of small, ask someone else to do it. Many contaminants have a significantly oily, rubbery or solvent type of smell. A musty smell may indicate excessive moisture is present. Being odorless, carbon monoxide won’t be detected by smell, but CO analyzers have become significantly cheaper and could well be used alongside the oxygen analyzers that are routine for Nitrox divers. If one notes CO or an unusual odor, abort the dive.

Finally, it would be useful if the dive industry, consumer agencies and researchers conducted regular surveys of air quality to provide a clearer picture of how often low-level contamination is happening.

This is a synopsis of the article “Compressed Breathing Air: The Potential for Evil from Within” by Ian Millar and Peter Mouldey. It was published in the journal Diving and Hyperbaric Medicine, September 2008. Undercurrent accepts full responsibility for any errors due to editing.

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