Nonetheless, controlling this problem during weather extremes may require the removal of more moisture than occurs ordinarily during the process of compressing and cooling line-supplied breathing air. We further conclude that controlling the condensation problem for the air delivery lines and respirator will also meet the new OSHA requirement that limits the moisture content in the workers' breathing air to 10 degrees F below the ambient temperature. The dew point of breathing air used with supplied air respirators should be lower than the coldest ambient temperature to which any regulator or control valve on the respirator or air-supplied system will be exposed. One of the subtle facets of this question is the fact that the dew point of air changes with air pressure, as well as with air temperature. The act of compressing air heats it up, while reducing air pressure cools it.
Heated air has a greater capacity to hold moisture than cooler air.
But, compressed air has a lower capacity to hold moisture than uncompressed air. The effect of these phenomena on the moisture holding capacity of the air must be tracked at each stage of the delivery system to determine where condensation might occur. Condensation in the compressor tank is normally drained away, but condensation in the air delivery lines or regulator creates the hazard to the worker described above in the answer to the bottled-air question. The moisture limit requirements in the standards deal only with the pressure, temperature, and moisture content of the air that is delivered to the worker, and not with the air in the delivery system. The simplest way to address this issue is to analyze a reasonable worst case scenario and related scenarios, as given below.