(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
appropriate. ACGIH and OSHA state that a ceiling value should not be exceeded even
instantaneously. . They denote a ceiling valuely a ACT preceding the exposure limit.
NIOSH also uses ceiling values. However, their ceiling values are more like a STEL. Many have
time limits (from 5 to 60 minutes) associated with the exposure.
Graph 5 illustrates
an exposure
that does not exceed a ceiling value of 5 ppm.
Graph 5
Example of an Exposure Compared to a Ceiling Exposure Limit
Peaks. Until recently ANSI, and OSHA where they
have adopted ANSI standards, had used a
peak exposure limit. This peak exposure is an allowable excursion above their ceiling values.
The duration and number of exposures at this peak value is limited. For example,
ANSI allowed
the 25 ppm ceiling value for benzene to be exceed to 50 ppm but only for 10 minutes during an 8
hour period. ANSI withdrew its exposure limit standards in 1982. With the revision of the PELs
in 1989, OSHA has dropped most of its peak values.
"Skin" Notation. While these exposure guidelines are based
on exposure to airborne
concentrations of chemicals. However, OSHA, NIOSH, ACGIH and AIHA recognize that there
are other routes of exposure in the workplace. In particular, there can
be a contribution to the
overall exposure from skin contact with chemicals that can be absorbed through the skin.
Unfortunately, there is very little data available that quantifies the amount of allowable skin
contact. But some organizations provide qualitative information about skin absorbable
(Created 12/02)
UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu
chemicals. When a chemical has the potential to contribute to the
overall exposure by direct
contact with the skin, mucous membranes or eyes, it is given a "skin" notation.
This "skin" notation not only points out chemicals that are readily absorbed through the skin, but
also notes
that if there is skin contact, the exposure guideline for inhalation may not provide
adequate protection. The inhalation exposure guidelines are designed for exposures only from
inhalation. If additional
routes of exposure are added, there can be detrimental effects even if the
exposure guideline is not exceeded.
