United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Airflow Measurement and Control for Supplied-Air Respirators

HPPOS-118 PDR-9111210275

Title: Airflow Measurement and Control for Supplied-Air


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

Applicability: All

Page Last Reviewed/Updated Thursday, March 29, 2012