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

• Author: International Labour Organization
• Pages: 192-195

192 Meetings-MESHA-Final Code-2010-10-0355-1-En.doc/v2

Appendix III

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. Purpose

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. 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. 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

the EL.

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.