Page 36 - OHS, July/August 2021

PPE: RESPIRATORY PROTECTION
Because the consequences of being exposed to high concentrations of some chemicals can result in severe health effects or death, it is very important that respirators are properly chosen and worn in the workplace.
APRs and ASRs can also have difffferent facepieces. ThThe most common are half-mask and full-facepiece. You can fifind quarter- mask, but they are very uncommon. Some respirators use a loose- fifitting facepiece where the facepiece does not come into contact with the wearer’s face. ThThe powered air purifying respirator (PAPR) is a special positive pressure APR using a battery powered fan to pull the air through the filter and then blow the air into the facepiece. As you can see from Table 1, whether you use an APR or ASR and the type of facepiece you use determines the level of protection that can be expected while using the respirator. In general, positive pressure respirators have higher APFs than negative pressure respirators and regulators that maintain a positive pressure inside the facepiece have the highest APFs.
Maximum-Use Concentration
APFs can then be used to calculate a maximum-use concentration (MUC). The MUC represents the highest concentration of a chemical for which you can use a particular respirator. To calculate the MUC, you must know the APF and the PEL (or the TLV or REL if you want) for the chemical. You simply multiply the APF by the PEL to obtain the MUC.
For example, the OSHA PEL for Methyl Ethyl Ketone (MEK) is 200 ppm. If you wanted to use a half-mask APR with the proper chemical cartridge the MUC would be 10 X 200 ppm = 2,000 ppm. That means you should be able to safely use a half-mask APR with the appropriate cartridges in an atmosphere up to 2,000 ppm MEK. If the concentration exceeded 2,000 ppm, you would have to use a respirator with a higher APF.
However, there is one other variable you must consider, the IDLH (immediately dangerous to life and health) concentration. If the concentration in the work environment exceeds the IDLH concentration, 29 CFR 1910.134 requires you to use specific types of ASRs and the MUC would then be set below the IDLH.
The National Institute for Occupational Safety and Health is one organization that publishes IDLH values for many compounds. The published IDLH for MEK is 3,000 ppm so your MUC is less than the published IDLH value. For gases and vapors, there is also a requirement to use a cartridge with an end-of-service-life indicator (ESLI) or develop a change out schedule. This is a requirement that many employers forget about. Another example would be if you
f
atmosphere-supplying respirators (ASRs). Basically, air passes through some filter in an APR which removes hazardous compound from the air prior to the air entering the wearer’s respiratory system. An important variable is ensuring the filter that is being used is specific for the hazardous chemical that is present in the work environment. In other words, you need a particulate filter for particulates and a specific gas or vapor cartridge for gases and vapors. Unlike the APR, the ASR provides “clean” air to the wearer that is separate from the air in the working environment.
With a supplied-air respirator (SAR), the air comes from a tank sitting in the neighboring work area or from a compressor, hopefully operating in a clean environment. The air might also come from a tank the wearer carries on their back (a self-contained breathing apparatus or SCBA). With all ASRs, the type of regulator will have a huge impact on the protection the respirator can provide. Some regulators will maintain a positive pressure inside the respirator facepiece at all times which does not allow outside air to enter the facepiece. This is important if the area might become dangerous.
Table 1 Assigned Protection Factors5
b
ba
a
s
si
i
c
ct
ty
y
p
p
e
e
s
so
o
f
r
re
es
sp
pi
ir
ra
a
t
t
o
or
rs
s
,
,
a
ai
ir
r
-
-p
p
u
u
r
r
i
if
f
y
yi
i
n
ng
gr
re
e
s
sp
p
i
ir
ra
a
t
t
o
or
rs
s
(
(
A
AP
PR
Rs
s)
)a
a
n
n
d
d
Type of Respirator 1,2
Quarter-Mask
Half-Mask
Full Facepiece
Helmet/ Hood
Loose Fitting Facepiece
Air-Purifying Respirator
5
310
50
Powered Air-Purifying Respirator (PAPR)
50
1,000
425/1,000
25
Supplied-air respirator (SAR) or airline respirator • Demand mode
• Continuous flow mode
• Pressure-demand or other positive pressure mode
------- ------- -------
10 50 50
50 1,000 1,000
------- 425/1,000 -------
------- 25 -------
Self-contained breathing apparatus (SCBA)
• Demand mode
• Pressure-demand or other positive pressure mode
(e.g., open/closed circuit)
------- -------
10 -------
50 10,000
50 10,000
------- -------
(Respiratory Protection, 1998)
32 Occupational Health & Safety | JULY/AUGUST 2021
www.ohsonline.com