192 Meetings-MESHA-Final Code-2010-10-0355-1-En.doc/v2
Standards with regard to occupational exposure limits
for hazardous substances, heat and cold, noise and
vibration and the assessment and monitoring of
agricultural hazards related to machinery
1.1. This appendix gives a general introduction to exposure limits for the use of employers
and others, and indicates where more information can b e o btained. Although some illustrative
values are quoted, it is not the purpose of this appendix to list values, because these change
continually as more technica l 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 e xpertise only. T hey 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 appendix.
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. In Japan, administrative control levels are p rovided by the competent authority. 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 cate gory 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 pr ovided 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) ―repres ent 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 ad ditional requirement to keep exposure as low as practicable, rather than simply below
2.4. It is also important to take i nto 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 req uires 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 average s, the control would have to be good enough to keep every 15-minute average
below the value.