Page 208 - IGC BOOK

Acute and Chronic Health Effects

Two different types of effect can occur when a person is exposed to a hazardous substance:

• Acute effects – the effects are short-term. They usually appear immediately or within a
relatively short time after exposure, that is, within a few minutes. Acute effects often occur as a
result of exposure to high levels of the substance, sometimes over very short periods of time. For
example, exposure to high concentrations of chlorine gas causes immediate irritation to the
respiratory system.

Acute effects will often disappear once exposure has stopped. However some substances, such as
cyanide, have such a pronounced acute effect that exposure is likely to be fatal.

• Chronic effects – the effects are long-term. Sometimes, the effects will persist for months or
years; in some cases, they will last a lifetime. Chronic effects usually occur as a result of exposure
to lower levels of the substance over long periods of time, are normally gradual and are often
progressive and irreversible. For example, respiratory sensitisation to flour dust can occur as a
result of repeated exposure to flour dust over several years. Once a worker is sensitised, their
reaction to flour dust may last the rest of their life. Some chronic health effects only become
apparent years after exposure, for example asbestosis occurs 10–20 years after multiple
exposures to asbestos.

Note that many hazardous substances can have both acute and chronic effects. For example,
exposure to high concentrations of industrial cleaning solvent can have a narcotic effect (acute),
and daily exposure to much lower levels can cause liver damage if it continues for many years
(chronic). Alcohol is another toxic substance that has both acute and chronic health effects.

Specific examples of chemical and biological agents hazardous to health and outlines of their
health effects can be found in the section on specific agents later in this element.

Classification of Hazardous Substance to Health

Chemicals can be broadly classified according to three types of danger:

• Physico-chemical – such as highly flammable, explosive or oxidising.
• Health – such as toxic or carcinogenic.
• Environmental – such as harmful to aquatic life.

ENSIGN| Unit IG2 – Element 7 – Chemical and Biological 3
Agents