Inspecting for Breathing Gas Contamination

A diver presenting symptoms finds oil and water in his tank during a visual inspection.

Reported Story

My buddy and I did our first dive to a maximum depth of 60 fsw (18 msw) for about 40 minutes. At the end of the first dive I felt dizzy and a little nauseous. We took about an hour break until my head cleared, and after eating a snack I felt better. I could think of no explanation for the dizziness. I was well rested, in good condition, ate a normal breakfast, and had been diving in the same location a couple weeks before. The weather conditions were calm and I am not prone to motion sickness.

We went in for our second dive and after about 15 minutes at a depth of 65 fsw (20 msw) I began to feel very nauseous. I signaled to my buddy that I felt ill and we began a gradual ascent and surfaced. On surfacing I felt extremely dizzy and had to use my buddy for support to keep from losing my balance. About one minute later I vomited. I dumped my gear and walked back to our vehicle, and my buddy collected my gear. After a half hour or so I felt well enough to leave the dive site so we drove home.

We analyzed the scenario and the only thing we could come up with was bad air, but we recognized that the chance of that happening was pretty rare. Nonetheless, that’s all we could come up with. The following day I called the dive shop where I got the air, told them what happened to me and asked if they had received any other calls about bad air. The owner told me they’d received no complaints or reports and they’d been using their air without any problems.

My buddy dropped our tanks off at a different dive shop, which is closer to home, and told them what had happened. The store owner suggested we do a visual inspection of the tanks. He called the next day and reported that 3 of the 4 tanks had puddles of water and an oily substance in them and only one tank was clean. He scrubbed the tanks and refilled them for us.

I called the original dive shop again and talked to an employee and told them what we’d found. He thanked me, and I received no further information.

After a few days my lungs seemed clear and I have not experienced any after effects. I think most people would have smelled the contamination, but my senses of smell and taste are somewhat impaired, so I didn’t notice any smell. Also, I was trying out a new mask, and what I did smell I attributed to the new mask rubber. One of my buddy’s tanks was mildly contaminated and he said he did notice the smell/taste, but he’d had his regulator serviced and thought maybe it was from that. He experienced no symptoms. The shop near the dive site completed a hydrostatic test on both of my tanks prior to filling. My buddy had his tanks visually inspected within the last year.


Health effects from breathing contaminated gas may depend on which contaminant the diver was exposed to. Among the most severe symptoms of breathing contaminated gas are impaired judgment and loss of consciousness, both of which may be deadly underwater. Observing the health of other divers who had their tanks filled at the same source may be helpful in determining whether a diver’s symptoms are related to contamination.

It is important to remember that identifying contamination incidents based on symptoms alone is difficult, as the associated symptoms are often similar to other diving-related and non-diving illnesses. Therefore, if a diver suspects exposure to bad breathing gas, he should seek medical evaluation and have the gas analyzed.
Hydrostatic testing and visual inspections are necessary and important for determining if a cylinder is safe to continue using, however these do not measure or identify contaminants in breathing gas. Hydrostatic testing is recommended every five years, and involves measuring the volume of the cylinder before and after pressurizing the tank to a test pressure. If the cylinder has an increase in volume above the standard, the cylinder fails the test and should no longer be used. An internal and external visual inspection for damage, corrosion, and appropriate tank markings is recommended annually. Both hydrostatic testing and visual inspection should be done by a trained professional.

In this case, oil and water were detected during the visual inspection, but it is unknown if other contaminants were present or the amount of oil in the air the diver was breathing without an analysis of the air sample. Unfortunately, following up with the dive shop where the air fill came from was unsuccessful in determining if the air supply is analyzed by an accredited lab.

Brittany Trout