Postdive Symptoms Possibly Caused by Gas Contamination

Two cases of postdive symptoms likely caused by contaminated gas. Predive checks and proper equipment maintenance may help to mitigate risk

Reported Story

Case One

Two experienced divers, an instructor and a divemaster, completed two dives in the same day. The first dive totaled 58 minutes to a maximum depth of 87 fsw (26 msw). The second dive totaled 56 minutes and the divers did not exceed a depth of 100 fsw (30 msw). The total bottom time for both dives was conservatively within safe decompression limits. The water temperature was warm (80-89° F, 27-32° C) and visibility was moderate (10-50 feet, 3-15 meters). Both divers reported having headaches after surfacing from each dive. No other symptoms were reported and the headaches subsided the next day. The breathing gas from the scuba tanks was not tested for contaminants before or after diving and both divers reported they did not use a CO monitoring device before diving

Case Two

The tanks used for this dive were hydrostatically tested and cleaned then they were stored for a few months before use. The diver performed a visual inspection before filling the tanks with air from a respectable dive shop. Prior to diving, the diver did a predive check and “the air tasted and smelled normal.”

The dive was at a shallow depth and short as the diver was removing marine life from buoys. After the first dive to a shallow depth of 5 fsw (1.5 msw), the diver felt nauseous. He went on a second dive to 12 fsw (4 msw) and felt dizzy upon surfacing. He said that both the nausea and dizziness subsided approximately 20 minutes after surfacing.

To make sure there was not any obvious taste or smell he might have missed during the predive check, he had his non-diving colleague breathe from the regulator for a few minutes and the friend also reported a headache after breathing the air. The colleague also reported no unusual smell or taste from the regulator. There was no smell, taste or any reason for concern during the predive check.

Other than the manual removal of marine life, the diver was not in any strenuous current and dive conditions were fairly calm. The maximum depth was 13 fsw (4 msw) and the dives lasted between 5 and 15 minutes. He had no significant medical history but was not well-rested due to a poor night’s sleep. He did not have the air in his tanks tested for contamination because there are no reliable labs that could carry out those kinds of tests in the location he was diving in. He did follow up with the dive operators who handled the tanks. The dive operator from the dive shop where the tanks were filled responded that there had been no reported issues by their staff or customers.


Symptoms associated with contaminants such as carbon monoxide (CO), carbon dioxide (CO2), volatile hydrocarbons, and oil particulates are often similar to other dive and non-dive related illnesses. For this reason, identifying breathing gas contamination based on symptoms alone can be difficult. However, there are a few things you can do to ensure the quality of gas you are using and when you do get symptoms, to determine if they are related to the gas quality.

Assess symptoms within the context of the dive exposure. For example, if you experienced symptoms after diving in challenging conditions or rapidly ascending to the surface, those exposures or events should be taken into consideration when identifying the root cause of postdive symptoms. Because divers typically get their tanks filled from the same source, observing the health and monitoring for related symptoms of fellow divers can be helpful in determining exposure to contaminated breathing gas. In both of these reported cases, more than one person had symptoms (headache, nausea) when they breathed gas from the same source. In the event that breathing gas contamination is likely, the diver should be medically evaluated and have the breathing gas tested to confirm exposure. Confirmation also ensures symptoms are diagnosed and treated accordingly.

Checking breathing gas quality before diving rather than only when symptoms occur during or after a dive is best practice to prevent contamination related injuries. Divers can incorporate practices into their predive safety check to help prevent injuries and illness related to breathing gas contamination. For instance, opening the valve on the scuba tank to smell and taste the gas flowing through the regulator is one way to detect bad breathing gas. If your breathing gas has an unusual odor or taste, do not dive with it — this is a red flag for oil or hydrocarbon contamination from the compressor or combustion engine exhaust. It is important to remember that not all contaminants can be detected this way; CO for example, is odorless and tasteless.

The diver in Case Two conducted a predive check and did not notice any unusual odor or taste, but still experienced symptoms possibly related to contamination. For this reason, electronic CO detectors or products such as CO-PROTM can be used to detect the presence of CO in breathing gas. Using a CO detector instead of a buddy to confirm contamination also prevents others from being exposed to CO. Personal CO detectors are especially important in remote locations where gas analysis services from accredited laboratories is not an option and medical evaluation is not easily accessible.

Brittany Trout