General ACOP
that the level of exposure is most unlikely ever to exceed the MEL, to comply
with this duty the employer should undertake a programme of monitoring in
accordance with regulation 10 so that he can show (if it is the case) that the
MEL is not normally exceeded, ie that an occasional result above the MEL is
without real significance and is not indicative of a failure to maintain adequate
control.
(d) Some substances for which MELs have been approved have been
assigned short-term MELs (eg 15-minute reference period). These
substances give rise to acute effects and the purpose of limits of this kind
is to render insignificant the risks to health resulting from brief exposures
to the substance. For this reason, short-term exposure limits should
never be exceeded.
(e) The extent to which it is required to reduce exposure further below the
MEL will depend on the nature of the risk presented by the substance in
question, weighed against the cost and the effort involved in taking
measures to reduce the risk.
Substances assigned an occupational exposure standard (OES)
37(a) OESs are approved by the Health and Safety Commission (HSC) and
are contained in the List of Approved OESs. The approval by HSC
limits the application of the OESs to people at work and to conditions
where the atmospheric pressure is normal (between 900 and 1100
millibars). For a substance which has been assigned an OES, exposure
by inhalation should be reduced to that standard. However, if exposure
by inhalation exceeds the OES, then control will still be deemed to be
adequate, provided that the employer has identified why the OES has
been exceeded and is taking appropriate steps to comply with the OES
as soon as is reasonably practicable. In such a case the employer’s
objective must be to reduce exposure to the OES; however, the final
achievement of this objective may take some time. Factors which need to
be considered in determining the urgency of the necessary action include
the extent and cost of the required measures in relation to the nature
and degree of exposure involved.
(b) For a single substance, control to the OES, or below it, can always be
regarded as adequate control of that substance for the purposes of these
Regulations, so far as exposure to inhalation is concerned.
(c) HSE’s publication EH 40 Occupational exposure limits (see page 13)
includes the lists of MELs and OESs, the approved methods for
averaging over the specified reference periods, an explanation of the
terms ‘respirable’ and ‘total inhalable’, and related material.
Inhaled substances not assigned MELs or OESs
7
38 The absence of a substance from the lists of MELs and OESs does not
indicate that it is safe. In these cases, exposure should be controlled to a level
to which nearly all the working population could be exposed, day after day at
work, without adverse effects on health. As part of the assessment required
under regulation 6, employers should determine their own working practices,
and in-house standards for control. These requirements will also apply in
situations where the substance has an OES, but it is not applicable for the
reasons described in the preceding paragraph. In some cases there may be
sufficient information to set a self-imposed working standard, eg from
manufacturers and suppliers of the substance, from publications of industry
associations, occupational medicine and hygiene journals.
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