Diving Air Compressor - Air Purity

Air Purity

The compressed air output by the compressor must be filtered to make it fit for use as a breathing gas. The following filters remove:

• Water, using silica gel, activated alumina or a molecular sieve
• Oil, using activated carbon or a molecular sieve
• Carbon monoxide, using catalyst

Oil, which must be used to lubricate the compressor's internal parts, can be particularly deadly if it enters the breathing gas and is inhaled as a mist. Petroleum-based oils cannot be absorbed and metabolized by the body and will coat the internal surfaces of the lungs, causing a condition known as lipoid pneumonia and leading to asphyxiation and death. For this reason, compressors must be carefully designed and maintained to ensure that no oil enters the breathing gas. Petroleum-based oils must never be used within the compressor. Instead, vegetable-based or specifically formulated synthetic oils are used, which can be safely absorbed and metabolized by the body in small quantities, should a malfunction occur.

Carbon monoxide (CO) is a gas that is present in the exhaust gas of internal combustion engines, including those often used to drive compressors. It also comes from the breakdown of lubricating oil when compressors run too hot. CO is odorless, colorless, and tasteless. CO is deadly even in small quantities, because it readily binds with the hemoglobin in red blood cells and thus destroys the blood's ability to carry oxygen. Diving compressors must be carefully designed and placed so that the compressor's intake is located in fresh cold air well away and upstream from any engine exhaust.

Periodically, the gas produced by a compressor must be tested to ensure it meets air purity standards. The following impurities are checked for:

• Carbon dioxide
• Carbon monoxide
• Lubricating-oil vapour
• Nitrogen dioxide
• Odor and taste
• Solid particles
• Water vapor