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
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
Applicability: All