2005-05 Compressed Air Quality

This article was first published in the BC / Yukon Local Section AIHA newsletter.

Compressed air is most commonly used by scuba divers, firefighters, paint booth operators, or anyone in a situation in which a clean source of air is not available from the surrounding atmosphere. While necessary for many occupations, breathing compressed air poses numerous risks. One such risk is air quality.

In the case of scuba divers, breathing air at depths under pressure means that the molecules making up each breath of air are more closely packed. The simplest way of demonstrating the compressed nature of air at depth is to imagine filling a balloon with air at depth and releasing it. In releasing the balloon, it will move toward the surface where surrounding pressures are lower. As a result of gas molecules moving apart because of lowered surrounding pressure, the balloon will expand as it moves towards the surface until finally bursting near the surface. The reverse is also true: a balloon filled at the surface and brought under pressure will compress, reducing in size as it is brought deeper. For scuba divers, the air can become thick and breathing can become difficult.

So what exactly does this mean to the health of a diver? If there is contamination in the air such as carbon monoxide, the increased density of the air allows more molecules to be inhaled with each breath. This means that higher levels of contaminants will enter the respiratory system and even low levels of contaminants at the surface can amount to very signicant levels under pressure. It follows, therefore, that the allowable level for carbon monoxide above water (at atmospheric pressure) is 25 ppm. The allowable level drops to 5 ppm under pressure.

In an effort to minimize these risks, the Canadian Standards Association publishes the CAN/CSA-Z180.1 and the CAN/CSA-Z275.2 to regulate the allowable levels of contaminants in pressurized air. These standards express the allowable levels of the following:

• carbon monoxide
• carbon dioxide
• methane
• total hydrocarbons
• halogenated hydrocarbons
• nitrogen dioxide
• nitrous oxide
• water
• oil
• particulates
• condensates, and others.

It is required that a check of compressed air quality is performed every six months.

Please contact CANTEST LTD. for more information, or to be placed on our “Compressed Air Check Reminder” system.

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