TM 1-1500-204-23-11
Figure 2-1. Carbon Fiber and Human Hair Diameters Compared to Filtration Level of HEPA Filter
2-4. OCCUPATIONAL EXPOSURE LIMITS. Occu-
(4) Skin Designation. Substances that may
pational Exposure Limits (OELs) have been estab-
cause adverse effects by being absorbed through the
lished that represent values under which it is believed
skin, mucous membranes or eyes are marked with
that nearly all workers may be exposed without
a skin designation. This serves as an alert that skin
adverse effects. OELs are based on the best available
exposure should be prevented or reduced as much
information from industrial experience and from exper-
as possible by using appropriate personal protective
imental studies on animals and/or humans. These
equipment (e.g., gloves, coveralls, and goggles).
limits are expressed as allowable airborne concen-
trations of the material in question. Army industrial
b. Threshold Limit Values (TLVs). Threshold limit
hygiene guidance promotes the use of the lower of
values are consensus recommendations published
either the Permissible Exposure Limit set by OSHA or
by ACGIH. They are not legally binding but are
the Threshold Limit Value set by the American Confer-
reviewed on a regular basis and are generally more
ence of Governmental Industrial Hygienists (ACGIH).
up-to-date than PELs. TLVs have the same categories
(TWA, STEL, C, and Skin) of exposure limits as the
a. Permissible Exposure Limits (PELs). Permis-
PELs. Most PELs were established when the OSHA
sible exposure limits are issued by OSHA and are
regulations were originally put in place in 1970.
the legally binding exposure limits. There are several
categories of PELs:
c. Use of Deined Exposure Limits. PEL and TLV
information, when established for the substance in
(1) Time Weighted Average (TWA). This is the
question, will be provided on the Material Safety Data
employee s average airborne exposure in any 8 hour
Sheets (MSDS). If a skin or S notation is used with
work shift of a 40 hour work week which shall not
the PEL or TLV, it indicates that the material may be
be exceeded.
absorbed through the skin, mucous membranes and
eyes. Use of the above units of measure to deter-
mine concentrations of suspect materials to ensure
(2) Short Term Exposure Limit (STEL). This is
PEL or TLV limits have not been exceeded requires
the short period TWA exposure assessment (usually
sophisticated measurement equipment and sampling
15 minutes) which shall not be exceeded during the
techniques. These techniques should be performed
work day.
by an industrial hygienist on a regular basis. For many
activities regular monitoring of the work place is not
(3) Ceiling (C). This is the employee s expo-
feasible, especially when deployed. Some advanced
sure which shall not be exceeded during any part of
the work day.