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RR427 - Moisture levels in compressed breathing air

The purity and quality of compressed breathing gases are specified to cover both the physiological and engineering safety aspects of the gas. Information relating to the permissible water content for compressed air at pressures less than 40 bar, as set out in BSEN 12021, is confusing. Consequently HSE contracted QinetiQ to develop guidance for the diving industry regarding the maximum permissible water content for compressed air at pressures less than 40 bar. A relationship, based on the Magnus equation, between the pressure within a compressed air system, the ambient temperature, the water content (ie volumetric humidity) and the pressure dew point (ie temperature at which liquid water or ice will form) was used to identify operational guidelines. Two tabular format operational guidelines, one simple and the other flexible in use, have been developed for the water content of compressed air at pressures less than 40 bar. The ‘simple’ tabular system is proposed as the preferred system.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2010-03-19