We all know that the OSHA Permissible Exposure Limits are
woefully out of date. They should be considered the legal limit but not the
safe limit. OSHA has three tables of
limits one for gases and vapors (Table Z-1) and one for particulates (Table
Z-3). That makes sense, however, they
also have a list of high hazard chemicals (Table Z-2). Most of us are familiar with the 8-hour
Time-weighted averaged Permissible Exposure Limit as we mentioned a second ago.
However, are you familiar with the Ceiling Limit? This level is the workers'
permitted instantaneous exposure level. By default if instantaneous
measurements are not possible then a default 15-minute period is sampled. Now here’s the twist, this is Table Z-1 world. Table Z-2 for the high hazard chemicals is
quite a different animal.
Table Z-2 chemicals have a third level OSHA calls a Maximum
Peak Concentration. OSHA says the worker
exposure level shall never exceed. OSHA further complicates this by specifying
a particular duration of time (e.g., 5
minutes, 10 minutes, etc.) for this exposure (and it various by the
chemical). However, the worker can be
exposed above the ceiling concentration (as found in Table Z-2) as long the
overall daily exposure stays below the Permissible Exposure Limit. I think an example is in order. We’ll take a
simple one Toluene.
A worker cleans metal parts to remove grease or paint in
preparation for the pickling process prior to coating the part. The worker wipes the parts down using a rag
soaked in the chemical stripper. The main ingredient in the stripper is
toluene. The operation only lasts 10-15 minutes at a time and the worker cycles
through the process 3-5 times per day.
Toluene – PEL = 200 ppm, Ceiling = 300 ppm, Maximum Peak
Concentration = 500 for 10 minutes.
The industrial hygienist had one pump running to evaluate
the 8-hour time-weighted average and one to evaluate the 10-15 minute
exposures. The following results were collected:
TWA = 100 ppm
Cycle 1 = 400 ppm (15 minutes)
Cycle 2 = 300 ppm (15 minutes)
Cycle 3 = 600 ppm (10 minutes)
Questions: Was
the worker overexposed to Toluene according to OSHA’s regulations?
How could the
industrial hygienist have sampled the operation differently?
You thought I was going to give you the answer….that would
be too easy. Give me your thoughts. Thanks for reading.
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