6. SOLVENTSExposure 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
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.
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.
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:
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:
|May cause cancer.
|Toxic: danger of serious damage to health by prolonged exposure through inhalation, in contact with skin and if swallowed.
|Avoid exposure - obtain special instructions before use.
|In case of accident or if you feel unwell, seek medical advice immediately (show the label where possible).
|During transport the containers must have UN number 1114 for identification
and the symbol of hazard class, which for benzene is Class 3 (flammable
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