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suspended form and which, according to latest findings, will generally not have
any health effects on, nor be unduly burdensome to, staff working in the laboratory
even after repeated or prolonged (8-hour working day) exposure, assuming a mean
working week of 40 hours.
At presence at free air at the same time several substances (e.g., carbon
monoxide and sulphurous anhydride; carbon monoxide, nitrogen dioxide and
sulphurous anhydride; hydrogen sulfide and carbon sulfur) maximum allowable
concentrations remain for each substance separately and the ratio of their
concentrations to MAC shall not exceed 1:

, (6.1)

At simultaneous presence at free air of several substances possessing
summation of action, the sum of their concentration during the calculation for a
below-mentioned formula shall not exceed 1:

1, (6.2)

where C , C , ..., C — the actual concentration of substances in free air;
n
1
2
MAC , MAC , ..., MAC — the maximum allowable concentrations of the
2
n
1
same substances.
Acute effects are those that show up immediately after a chemical exposure
occurs. A good example of an acute effect is the spillage of acid on the skin – a
chemical burn will occur immediately. Chronic effects are those that occur after a
significant amount of time passes and usually are the result of multiple exposures
over a period of time. Cancer is a typical example of a chronic effect because
cancers caused by chemical exposures often do not show up until twenty or more
years after the initial exposure.
Hazardous chemicals are classified depending on how they affect human
health, see table 6.1.

Table 6.1 – Effects of chemicals on the body
Biological effect on the body

Carcinogen A chemical that causes or potentially causes cancer (e.g. asbestos,
formaldehyde)

Corrosive A chemical that causes visible destruction of, or irreversible
alterations in, living tissue by chemical action at the site of contact
(e.g. hydrochloric acid)

Biological effect on the body

Irritant A chemical that is not corrosive, but that causes reversible
inflammatory effects on living tissue at the site of contact (e.g.
strong solvents)

Mutagen A chemical that damages chromosomes (e.g. benzene)

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