Three Ways to Tell if Your Air Tank Gas is Bad


For divers, there is nothing more important than their breathing gas.  Whether it is compressed air, nitrox, or a mix, a divers’ predive checklist is sure to have a check for breathing gas.  Quality is just as important as quantity when it comes to the breathing gas in a tank.  Trace amounts of contamination can lead to unconsciousness, incapacitation, or death.

Causes of Contamination

There are a variety of forms that can cause breathing gas contamination:  compressor system malfunctions, driver cylinder problems, and improper gas mixtures.  Divers need to take responsibility for confirming the quality of their own gas.  Fortunately, there are several different ways for divers to analyze gas mixtures for contaminants.

The Sniff Test

The simplest way to determine the quality of air is the “sniff test.”  A diver simply opens the valve and smells the gas that escapes to detect any suspicious odors.  The test may be crude, but it is effective to detect oil, diesel fumes, and other combustible products that have a scent.  Unfortunately, carbon monoxide (CO) is odorless and colorless and is not detected by the sniff test.

CO Detectors

CO levels are often measured with color-changing sensors.  There are detectors that tell if there is too much CO in the gas, but not how much CO is actually contained inside.  There are sensors that use a small pump to draw a measured amount of air through a calibrated color-changing tube.  Depending on the amount of CO contained in the air sample, a scale on the side of the tub reflects the amount with varying color changes.

Electronic CO-monitoring devices, in metal-oxide and electrolytic types, work in different ways, but both accurately measure the amount of CO in an air sample.  Metal-oxide devices use metal-oxide and measure temperature changes.  Electrolytic CO detectors are the most accurate types of CO sensors, but reflect this accuracy in price.

Nitrox Analyzers

With the growing popularity of nitrox, nitrox analyzers are found in most dive shops.  However, these sensors actually measure the level of oxygen in a particular nitrox gas mixture.  These monitors are typically accurate unless the unit goes from cold conditions to suddenly warm conditions or vice versa.

Symptoms of Contaminated Gas

  • General Contamination – Oily taste, oily smell, or other foul odors
  • Carbon Monoxide Poisoning – Headache, dizziness, nausea, vomiting, weakness, chest pain, and confusion
  • Oxygen Toxicity – Tremors, ringing in the ears, nausea, tunnel vision, and seizures

If a diver experiences any of these symptoms, the dive should be stopped immediately and the diver should return to the surface.