Handbook of Solvents - George Wypych - ChemTech - Ventech!

56 George Wypych
2.3.14 OCCUPATIONAL EXPOSURE INDICATORS
The measurement of solvent concentration in the workplace place is required by national
regulations. These regulations specify, for individual solvents, at least three different concentrations
points: the maximum allowable concentration for an 8 hour day exposure, the
maximum concentration for short exposure (either 15 or 30 min), and concentration which
must not be exceeded at any time. These are listed in the regulations for solvents. The listing
is frequently reviewed and updated by the authorities based on the most currently available
information.
In the USA, the threshold limit value, time-weighted average concentration,
TLV-TWA, is specified by several bodies, including the American Conference of Governmental
Industrial Hygienists, ACGIH, the National Institute of Safety and Health, NIOSH,
and the Occupational Safety and Health Administration, OSHA. The values for individual
solvents stated on these three lists are very similar. Usually the NIOSH TLV-TWA are
lower than on the other two lists. Similar specifications are available in other countries (for
example, OES in UK, or MAK in Germany). The values for individual solvents are selected
based on the presumption that the maximum allowable concentration should not cause
injury to a person working under these conditions for 8 hours a day.
For solvent mixtures, the following equation is used in Germany to calculate allowable
limit:
I
MAK
i= n
= ∑
i = 1
c i
MAK
i
[2.3.11]
where:
IMAK evaluation index
c concentrations of components 1, 2, ..., n
MAK maximum permissible concentrations for components 1, 2, ..., n
The maximum concentrations for short exposure is the most frequently limit specified
for an exposure of 15 min with a maximum of 4 such occurrences per day each occurring at
least 60 min apart from each other. These values are 0-4 times larger than TLVs. They are
selected based on the risks associated with an individual solvent.
Solvent concentrations which should not be exceeded at any time are seldom specified
in regulations but, if they are, the values stated as limits are similar to those on the three lists.
In addition, to maintaining concentration below limiting values, adequate protection
should be used to prevent the inhalation of vapors and contact with the skin (see Chapter
24).
2.3.15 ODOR THRESHOLD
The principal for odor threshold was developed to relate the human sense of smell to the
concentration of the offending substances. If the substance is toxic, its detection may provide
early warning to the danger. However, if the odor threshold is higher than the concentration
at which harm may be caused it is not an effective warning system. Toxic substances
may have very little or no odor (e.g., carbon monoxide) and an individual’s sense of smell
may vary widely in its detection capabilities. A knowledge of odor threshold is most useful
in determining the relative nuisance factor for an air pollutant when designing a control system
to avoid complaints from neighboring people surrounding a facility. Regulations often
state (as they do for example in Ontario, Canada) that, even when the established concentra-