Introduction to Health and Safety at Work

Chemical and biological health hazards and control
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risks can usually be minimized or removed by following 
the instruction provided with the substance (e.g. by using 
personal protective equipment). There are many house-
hold substances which fall into this category including 
bitumen-based paints and paint brush restorers. Many 
chemical cleansers, such as trichloroethylene, are cat-
egorized as harmful. It is very common for substances 
labelled harmful also to be categorized as irritant.
Toxic
substances are ones which impede or prevent the 
function of one or more organs within the body, such as 
the kidney, liver and heart. A toxic substance is, there-
fore, a poisonous one. Lead, mercury, pesticides and the 
gas carbon monoxide are toxic substances. The effect 
on the health of a person exposed to a toxic substance 
depends on the concentration and toxicity of the sub-
stance, the frequency of the exposure and the effective-
ness of the control measures in place. The state of health 
and age of the person and the route of entry into the 
body have infl uence on the effect of the toxic substance.
Carcinogenic
substances are ones which are known or 
suspected of promoting abnormal development of body 
cells to become cancers. Asbestos, hard wood dust, 
creosote and some mineral oils are carcinogenic. It is 
very important that the health and safety rules accom-
panying the substance are strictly followed.
Mutagenic
substances are those which damage genetic 
material within cells causing abnormal changes that can 
be passed from one generation to another.
Each of the classifi cations may be identifi ed by 
a symbol and a symbolic letter – the most common of 
these are shown in Figure 14.1.
The effects on health of hazardous substances may 
be either acute or chronic.
Acute
effects are of short duration and appear fairly 
rapidly, usually during or after a single or short-term 
exposure to a hazardous substance. Such effects may 
be severe and require hospital treatment but are usually 
reversible. Examples include asthma-type attacks, nau-
sea and fainting.
Chronic
effects develop over a period of time which may 
extend to many years. The word ‘chronic’ means ‘with 
time’ and should not be confused with ‘severe’ as its use 
in everyday speech often implies. Chronic health effects 
are produced from prolonged or repeated exposures to 
hazardous substances resulting in a gradual, latent and 
often irreversible illness, which may remain undiagnosed 
for many years. Many cancers and mental diseases fall 
into the chronic category. During the development stage 
of a chronic disease, the individual may experience no 
symptoms.