Breathing Air Contamination

The quality and purity of the air you breathe while scuba diving is an important safety factor that you may take for granted. We live and dive in South Florida where we are surrounded by excellent scuba shops that provide us with high quality diving cylinder refills of both air and nitrox.  This, however, has not always been the case, and may not be the circumstance you find yourself in if you dive in remote portions of the world.

What are the most common contaminants in diving air?  How might you detect each contamination, and what are its consequences?

Water:  When humid air is compressed, water condenses within the SCUBA compressor. The typical multistage SCUBA compressor has moisture traps after each stage. If these moisture traps malfunction, significant water can be discharged from the compressor along with the airstream. If the entrained water is sufficient, it may overwhelm the final discharge filter, and allow some water to be pumped into your SCUBA cylinder. Small amounts of water in a SCUBA cylinder generally go undetected until the cylinder is visually inspected. If a large amount of water enters a SCUBA cylinder it may pass through the cylinder valve into a regulator when the diver is inverted. This may cause momentary malfunction of the regulator and the diver may get a mouthful of water with a foul taste.  

Compressor oil: The typical scuba compressor has reciprocating pistons that move within cylinders, somewhat similar to an internal combustion engine. These reciprocating pistons are lubricated with oil just as they are within your automobile engine. However, the oil used in SCUBA compressors is food grade oil that is safe for human consumption.  Some of this compressor oil is discharged from the compressor along with the output air. It normally is removed by the final condensate trap and the final output air filter present on the compressor. However, if the output air filter malfunctions or is not changed on schedule, oil can pass into your SCUBA cylinder. Small amounts of oil in a SCUBA cylinder may cause the air to taste or smell or may go undetected until the cylinder is visually inspected. If a large amount of oil enters a SCUBA cylinder it may pass through the cylinder valve into a regulator when the diver is inverted. This may cause momentary malfunction of the regulator and the diver may get a mouthful of oil with a foul taste.  

Carbon Monoxide (CO):  Carbon monoxide may pass into an air intake system for a SCUBA compressor when the air intake is close to the exhaust of an internal combustion engine.  This is most commonly associated with a SCUBA compressor that is driven by a gasoline or diesel engine. However, it could also occur if a running automobile, truck or boat engine exhaust is close to the air intake of the SCUBA compressor (while your cylinder is being filled).  The output air filter of a modern SCUBA compressor is designed to remove CO but there’s always the possibility of a malfunction or lack of timely filter replacement.

Carbon monoxide contamination in your breathing air is a serious issue.  It may cause headache, dizziness, nausea, vomiting, shortness of breath, confusion and loss of consciousness.

Your Takeaway:  Have your SCUBA cylinders filled at a reputable SCUBA shop. If you’re at an unfamiliar shop, ask to see the SCUBA compressor, and inquire when the output air filter was last replaced.  If you don’t come away with a warm and fuzzy feeling, go somewhere else for your tank fill.

Be safe, Dive safe

And, may your SCUBA regulator always taste and smell like fresh mountain air!