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Obtaining knowledge to describe these three factors is the cornerstone or
foundation of most chemical risk assessments. As these data are not always
available, many risk assessments require that estimates or judgements be made
regarding some data inputs or characterizations.
Consequently, risk assessment results have associated uncertainties, which
should be characterized as much as possible.
There are measures or precautions are necessary to control these risks:
- Elimination: change the process or activity so that the hazardous
substance is not used or is not generated;
- Substitution: replace it with a safer alternative;
- Isolation: separate the hazardous substances from workers;
- Engineering controls: use physical measures to minimize workplace
contamination, e.g. extraction at source by LEV (local exhaust);
- Administrative controls: use of safe work practices and procedures to
minimize contamination, e.g. good hygiene procedures;
- Personal Protective Equipment (PPE): provide facemasks, gloves,
protective clothing, etc., but only as a last resort or “belt and braces” measure.
The control measures themselves must also be checked and maintained at
regular intervals. For example, local exhaust ventilation equipment should be
examined at suitable intervals against its specification to ensure its continued
effectiveness. Sometimes it is necessary to monitor worker exposure at regular
intervals (e.g. by measuring concentrations in air) to ensure exposure limits are not
exceeded. Health surveillance may also be required in certain circumstances. All
these measures must be fully specified in writing.
Chemicals can exist in the form of:
a) Solids such as dusts, fumes, fibres (e.g.wood dust, bitumen fumes and

asbestos fibre).
b) Liquids, mists (e.g. liquid bleach and mineral oil mist).

c) Gases, vapours (e.g. carbon monoxide gas and solvent vapour).
d) Any substance, in gas, liquid or solid form, which has the potential to
cause harm, is referred to as a hazardous or dangerous substance. Such substances
include those:
e) Brought directly into the workplace and handled, stored and used for
processing (e.g. solvents, cleaning agents, glues, resins, paints).
f) Generated by a process or work activity (e.g. fumes from
welding/soldering, dust from machining of wood, flour dust, solvents).
g) Generated as waste or residue (e.g. fumes from soldering irons, carbon
monoxide from exhausts). Substances can be considered hazardous not only
because of what they contain (i.e. their chemical ingredients) but because of the
form or way in which they are used at the workplace. In addition to their effects on
human health, some chemicals also present physical hazards such as the potential
to ignite or support combustion of other substances (oxidiser) and the potential to
explode. The physical, environmental and human hazards of a chemical substance
must be considered when conducting a risk assessment in the workplace. How do

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