Airflow Measurement and Control for Supplied-Air Respirators
See the memorandum from J. E. Wigginton to J. H. Joyner (and others) dated August 5, 1982. It provides guidance on assuring that the required minimum airflow is being provided to each individual respirator user when several users are sharing a single air regulator manifold supply.
In response to a Regional inspector's request, the Los Alamos National Laboratory (LANL) was asked how IE can be assured that required minimum airflow is being provided to each individual respirator user when several users are sharing a standard air regulator manifold supply. This discussion is limited to continuous-flow Type C respirators. The airflow requirements of regulator-controlled airline respirators (such as pressure-demand) are so much less than continuous-flow devices, that adequate airflow is not usually a problem.
There appears to be a misunderstanding on what flow measurement is appropriate when adjusting the air pressure on an airline. It is the airflow about the head and face of the respirator wearer that largely determines the protection provided by the device. Therefore, one needs to be concerned only with the airflow at ambient conditions.
Furthermore, the temperature and pressure at most actual working conditions are sufficiently close to standard conditions that either may be used for the calculations. An exception would be for work at high altitude, such as above 6000 ft at Los Alamos, where the atmospheric pressure is less than 80% of sea level, requiring corrections for the difference in flow.
Manufacturers of airline respirators include instructions specifying a range of air pressure required to produce the needed flow rates based on both the lengths of hose used and the number of sections connected together. Concern with the latter is because of the considerable pressure drop in the quick-connect fittings between each section of hose. If the appropriate pressure for the total length of hose is used, ample flow should be available.
Problems may develop when more than one user is connected to an air manifold with a single regulator and pressure gauge. If each user has different hose lengths or respirators with different air pressure requirements, this manifold arrangement should not be used. In this case, it is difficult to determine if each user is receiving the required airflow. A much better approach would be a system where individual control is provided with a separate regulatory and pressure gauge for each user.
In addition, the user has the option of measuring the airflow at the respirator. This is most easily done during the set up of the system before work begins. The lengths of hose required for the job should be connected. In most systems, there is a belt-mounted valve or regulator. The high-pressure air hose plugs into this valve, and a low-pressure breathing tube runs to the facepiece or hood.
The end of the breathing tube is the best point at which to take the flow measurements. Disconnect the tube from the facepiece and insert into a calibrated rotameter or other airflow measuring instrument, and then, the line pressure may be adjusted to obtain the desired airflow. It is recommended that any air supply system be designed to deliver greater than the minimum required (4 cfm for tight fitting facepieces and 6 cfm for hoods), but the flow should be adjusted so as not to be so high as to be uncomfortable for the wearer. If the pressure required for each configuration of hose and respirator combination is recorded, future respirator set up of this type will be made considerably easier. Any questions as to the adequacy of airflow can be easily answered by actually measuring it.
One final important point must be made about the use of appropriate hose fittings. It is extremely important in a work place using a variety of different piped fluids, that the fitting used for breathing air be different and incompatible with any other in the plant. Supplied air respirators may be ordered with one of several different quick-connect fittings, and, if any one of these is not in use in the plant, there is no problem. However, in the event that all of the hose fittings available for the respirator manufacturer are already in use, then a different, unique fitting will have to be selected for breathing air.
The user organization must then replace all of the fittings on the valves and hoses with the special fitting. Since the resistance of the new fitting may not be known, the airflow to respirator with various hose lengths should be measured as discussed above.
Regulatory references: 10 CFR 20.103, 10 CFR 20.1703, Regulatory Guide 8.15
Subject codes: 8.10