Attention users of air compressors for air-supplied respirators

February 1996

The Department of Labor and Industries has conducted numerous compliance inspections within the asbestos abatement industry and has determined that ambient air pumps regularly fail to supply the minimum required air flow necessary for full-facepiece, continuous-flow airline respirators. Air flow measurements have been found to range from 1 cubic foot per minute (CFM) to 5 CFM, with most measurements falling below the minimum Federal requirement of 4 CFM. Air flows also were consistently below the 6 CFM requirement for full-facepiece, continuous-flow airline respirators equipped with HEPA egress cartridges used in asbestos removal.

The 6 CFM flow rate is a special requirement that applies when asbestos removal work is performed inside negative pressure enclosures. Operation of any continuous-flow airline respirator system, below these air flow requirements will cause leakage of air contaminants into the face piece -- a violation of state occupational health standards.

The use of continuous flow respirators has proliferated in several industries as a result of safety and health regulations and a heightened awareness of health hazards generated by many harmful or toxic materials. The need for inexpensive and portable breathing air sources has triggered the wide spread usage of ambient air pumps. An ambient air pump is generally a small portable rotary vein compressor driven by a 1.5 or 2 horsepower electric motor which can be operated at 15 amps and 110 volts. In the asbestos abatement industry, ambient air pumps are often the air supply system of choice because they are inexpensive and presumed to be easily operated.

Unlike high pressure compressors, in particular those with reservoir tanks, the air supply from an ambient air pump is directly affected by the configuration and location of the system components. Air supply filters, hose length, hose diameter, bypass valves, maintenance and number of employees utilizing the system all affect system air supply flow and quality. These contributing factors are rarely understood.

If low horsepower ambient air pumps must be used, the Department recommends daily air flow measurements of the respirator air supply. More frequent air flow measurements may be necessary when system components are modified or when the number of users on the system increases. A precision rotometer or similar device which accurately displays air flow rates in a range of 1 to 10 CFM, is required to assess flow. Precision rotometers must be used according to manufacturer's specifications to display accurate flow rates. Measurements should be taken at the respirator facepiece while the system is configured and operated as it will be used. When air flow fails to meet minimum requirements, the respirator cannot be used.