6. SOLVENTS
Exposure to solvents and other organic liquids is one of the most common
chemical health risk at places of work. Most of the organic solvents are
combustible, often highly volatile and extremely flammable and they should
always be handled with care. Some solvents produce vapours which are heavier
than air. These may move on the floor or ground to a distant ignition source,
such as a spark from welding or caused by static electricity. The vapours
may also explode from smoking. Vapours of solvents can also accumulate
in confined places and stay there for a long time, presenting risks for
health and property.
Solvents enter the body by inhalation, by swallowing and through the
skin. The effect depends on several factors, such as
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how easily the solvent evaporates at the ambient temperature?
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what are the characteristics of that solvent; is it water soluble or able
to dissolve fats?
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what is the concentration of the solvent in the air at the place of work?
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what type of work is involved, light or heavy? (Panting increases the amount
inhaled.)
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how long does the exposure last?
Solvents, their vapours and mists have various effects on human health.
Many of them have a narcotic effect, causing fatigue, dizziness and intoxication.
High doses may lead to unconsciousness and death.
Exposure to large doses of solvents may slow down reaction- time and
affect rational judgement. This may increase the risk of accidents both
at work and outside, such as in the traffic on the way back home.
Solvents irritate the eyes and the respiratory tract.
Solvents clean and defat not only metal plates in industrial processes
but also the skin. This is a very common cause of skin disorders and dermatitis.
Some solvents penetrate the skin and enter the blood circulation.
Solvents may damage the liver, kidneys, heart, blood vessels, bone marrow
and the nervous system.
The solvents which pose the most serious risk to health should be substituted
by less hazardous ones. If this is not possible with regard to the workprocess,
at least the conditions during handling should be adjusted so that there
is no risk of skin contact and that the concentration of vapour in the
air is kept low. This may be achieved, for example, by using a closed process.
Amongst the most hazardous solvents are benzene, carbon disulphide and
carbon tetrachloride.
Solvents are excreted in urine and sweat or they may be exhaled.
Workplace controls and practices
Good work practices and training can help to reduce hazardous exposures.
For most of the hazardous solvents it is possible to find a substitute
with the same characteristics but less drastic effects on health.
Ventilation is important and it should be considered carefully when
using solvents.
Equipment (fire extinguishers, absorbant material, etc.) should be considered
and provided for situations such as spillage or emergency.
Personal protective equipment such as aprons, gloves and masks with
filters should be available where needed, and they should be used according
to the recommendations. Storage of this equipment should be in a clean
place away from possible contact with solvent vapours.
Picture 46
Picture 47
BENZENE
Benzene is a colourless, flammable liquid with a pleasant odour. It is
used as a solvent in many areas of industries, such as rubber and shoe
manufacturing, and in the production of other important substances such
as styrene, phenol and cyclohexane. It is essential in the manufacture
of detergents, pesticides, solvents and paint removers. It is present in
fuels such as in gasoline up to the level of 5%.
The Threshold Limit Value (TLV) in the workplace air over an 8- hour
working day (as recommended in many countries) is 10 ppm (or 32 mg/m3).
Some countries recommend even lower levels. The odour threshold is 12 ppm.
The odour serves only as a warning of exposure. If you are handling benzene
without smelling it, this does not mean that there is no exposure.
Health effects
Benzene enters the body through inhalation and it may pass through the
skin. Exposure to low concentrations of benzene vapour or to the liquid
which has penetrated the skin may cause dizziness, lightheadedness, headache,
loss of appetite and stomach upset. Exposure can also irritate the nose
and throat. High exposures to benzene may cause irregularities in the heart
beat which can lead to death.
Repeated exposure can damage the bone marrow, which is the blood-forming
organ, causing a condition called aplastic anaemia. This may also lead
to death.
Long-term health effects may follow when exposure to benzene has lasted
for a long period of time; several months or years. Benzene is a cancer-causing
substance: a carcinogen. There is sufficient evidence that benzene causes
leukaemia in exposed workers. Many scientists say that there is no safe
level of exposure to a carcinogen.
Benzene may cause birth defects in animals. Until further testing has
been done it should be handled very carefully as a possible agent causing
birth defects in humans as well.
In several countries there are severe restrictions for using and selling
benzene.
Workplace controls and practices
As a solvent benzene can be substituted with a variety of less
hazardous ones. Toluene is a similar solvent to benzene. It has the general
adverse effects of solvents but it has been shown neither to cause cancer
nor to damage the bone marrow. White spirit is often used as a substitute
for more dangerous solvents. Less volatile solvents, such as xylene and
mesitylene, have the same type of characteristics as toluene. Gasoline
should never be used as a substitute. It may contain benzene, tetraethyl
lead or other hazardous substances.
Engineering control is the most effective way of reducing exposure
where substitution is not possible. Operations with benzene can be enclosed
and/or exhaust ventilation can be provided at the site of chemical release.
Isolation of operations can also reduce exposure.
Personal protective equipment, for example, breathing protection,
is sometimes necessary although less effective. However, recommendations
are only guidelines and may not apply to every situation.
Benzene is filtered with a mask and filter type A (for organic solvents
with boiling point over 65 °C). Improper use of the respirator is dangerous.
The best choice would be a helmet with fresh air supply and a face piece
operating with positive pressure, blowing clean air from inside the helmet
or hood outward. Not all types of gloves can resist the strong solvent
power of benzene. Viton or PVA gloves are recommended although even they
have limited resistance to benzene.
When clothing is contaminated it should be changed promptly to avoid
intake through the skin.
Eating, smoking or drinking should not be allowed where benzene (or
other hazardous solvents) are handled.
Handling and storage
Benzene vapour is heavier than air and may move along the floor to a
distant ignition source. Smoking and open flames are prohibited where benzene
is handled, used or stored. It should be stored in tightly closed containers
in a cool well- ventilated area away from heat.
Metal containers need to be grounded to avoid ignition from sparks caused
by static electricity. Attention should be paid to electrical equipment,
this should be explosion-proof. Benzene reacts violently with oxidizing
agents, such as permanganates, nitrates, peroxides, chlorates and perchlorates.
If benzene is accidentally spilled, the following steps should be taken:
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Restrict persons from the area of spill unless they wear protective equipment.
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Remove all ignition sources.
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Ventilate the area of spill or leak.
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Absorb the liquid in inert material, such as vermiculite, dry sand, earth
and deposit in sealed containers.
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Do not wash benzene into the sewage system. It may cause an explosion.
Benzene is a hazardous waste.
Large spills should be cleaned by experts from the fire department.
Classification and labelling
Benzene is classified as toxic and highly flammable in the EU. Labels
on bottles or containers should carry symbols corresponding to `highly
flammable' and `toxic', to indicate the risks. Risk (R) and safety advice
(S) phrases are: |
