Occupational exposure limits for hazardous substances, electric and magnetic fields, optical radiation, heat, noise and vibration

Author:International Labour Organization
Annex V
Occupational exposure limits for hazardous
substances, electric and magnetic fields, optical
radiation, heat, noise and vibration
1. Purpose
1.1. This annex gives a general introduction to exposure limits for the use of employers and
others, and indicates where more information can be obtained. Although some illustrative values are
quoted, it is not the purpose of this annex to list values, because these change continually as more
technical information becomes available, and it is the responsibility of the competent authority to
specify which exposure limits should be used and how.
1.2. Certain standard-setting bodies rely on technical expertise only. They do not accurately
reflect the views of the social partners, e.g. trade unions. This should be taken into account when
referring to the standards mentioned in this annex.
2. General
2.1. An exposure limit (EL) is a level of exposure specified by a competent authority, or some
other authoritative organization such as a professional body, as an indicator of the level to which
workers can be exposed without serious injury. It is used as a general term and covers the various
expressions employed in national lists, such as “maximum allowable concentration”, “threshold
limit value”, permissible level”, “limit value”, “average limit value”, “permissible limit”,
“occupational exposure limit”, “industrial hygiene standards”, and so on. The exact definition and
intended application of ELs vary widely from one authority to another, and the underlying
definitions and assumptions and the requirements of the appropriate competent authority should be
taken into account if they are used. For example, some authorities have promulgated ELs that are
used as legally permitted “safe” levels of exposure and are intended to protect against injury, not
against every health effect. Other authorities provide for limits intended as guidelines or
recommendations in the control of potential workplace health hazards.
2.2. Administrative control levels are provided by the competent authority in Japan. These
levels are not limits for individual exposure; they constitute an index to determine the control
category (level of cleanliness), and to assess the adequacy of control measures in the working
environment. The control category is based on the results of working environment measurements in
the work area.
2.3. An important example of the caution to be applied in using ELs is provided in the
introduction to the annual publication Threshold limit values for chemical substances and physical
agents and biological exposure indices of the American Conference of Governmental Industrial
Hygienists (ACGIH): threshold limit values (TLVs) “represent conditions under which it is believed
that nearly all workers may be repeatedly exposed day after day without adverse health effects.
Because of wide variation in individual susceptibility, however, a small percentage of workers may
experience discomfort from some substances at concentrations at or below the threshold limit; a
smaller percentage may be affected more seriously”. Consequently, any EL represents a risk that is
felt to be acceptable based on a particular criterion, and where such limits are promulgated there is
usually an additional requirement to keep exposure as low as practicable, rather than simply below
the EL.
2.4. It is also important to take into account the averaging period for which the limit is
intended. Some limits are ceiling values to be continuously applied; others apply to average
exposures over a period of up to several years. A short-period limit requires stricter control than a
longer-period limit at the same exposure value. For example, a limit applying to a month might
allow the exposure to range above the value for days at a time, provided there was a compensating
period of low exposure that maintained the monthly average. If the same value were applied to 15-
minute averages, the control would have to be good enough to keep every 15-minute average below
the value.

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