DAN Will Help Divers with Breathing-Gas Analysis

Reported Story: Case 1

I was checking my regulator during a pre-dive check and I noticed my air tasted weird. Not knowing what the unusual taste was, I began my dive. Shortly after entering the water, I started having issues with my vision and difficulty breathing at 25 fsw (8 msw). I signaled to my dive partner and we surfaced, however both of us barely made it back to the boat. I exited the water with the help of a deck hand and a witness on board the boat said my eyes were rolling upward in my head.

Later that day I experienced vomiting and difficulty breathing for approximately one hour. My dive partner as well as another diver also experienced the same symptoms as me. The dive shop where the tanks were filled was contacted and advised to check the equipment used to fill tanks, but the dive shop staff denied any issues. I was informed the dive shop would send copies of the tank inspections; however that never happened.

Reported Story: Case 2

A diver experienced a bad taste in the air from the regulator, shortness of breath, dizziness, light-headedness, and nausea while descending past 60 fsw (18 msw). The reported symptoms increased until the dive was aborted at 90 fsw (27 msw). The diver and his dive buddy surfaced with a normal ascent rate (>60 fsw/minute). Both divers slowly returned to the shoreline and rested. The injured diver was alert but fatigued with persisting symptoms of dizziness and nausea.

While removing their dive gear, the divers noticed the air from the injured diver's tank smelled funny and was described as a strange chemical smell, not like exhaust or fuel. The diver experienced tightness of the chest, congestion, coughing and stomach aches. The diver did see a physician and after a few days, the symptoms subsided.

The injured diver did not get the tank tested themselves, due to gas analysis cost; however the dive shop who issued the tank was notified of the suspected bad air in the tank. Others also reported to the dive shop they suspected the tanks were being filled with contaminated air, possibly from oil leaking from the compressor used to fill the tanks. However, it is unknown if the dive shop addressed the issue.


In general, incidents involving breathing bad gas, whether that be compressed air, nitrox, trimix or other mixture, are rare. Sources of bad breathing gas vary, but could include impurities found in the air used for filling tanks, contaminants produced by a compressor, or the actual tank may be damaged or tainted. If the compressed gas from a tank has an unusual smell or taste when breathed in, a diver should never proceed to use that supply for diving. Unfortunately, not all contaminants have an odor or taste and some, such as carbon monoxide, may go undetected. If a diver suspects they were exposed to bad breathing gas it is important to be evaluated medically and if possible, have the tank tested to verify and confirm contamination. It is difficult to base poisoning on symptoms alone, as these associated symptoms such as headache, nausea, fatigue, and stomach ache are often similar to other dive related illnesses.

Issues associated with breathing contaminated gas are occasionally reported, however it is suspected the number of incidents associated with contaminated tanks is often under-reported. To encourage divers to report compressed gas contamination, DAN is offering to assist with the gas analysis of reported and approved cases. If you have an incident possibly related to breathing contaminated gas and have lawful control of the tank, please preserve your tank and contact DAN Research by phone (919-684-2948, ask for Research department) during regular office hours (8:30am-5:oopm EST) or through the online incident reporting system.

— Brittany Trout, DAN Research Associate

Additional Readings

Rossier, Robert N. "When Gas Goes Bad," Alert Diver, Fall 2010.