There are a variety of technical measures that can be used to prevent chemical hazards at source and / or reduce personnel exposure [Ref. 1 & 2; also http://www.ilo.org].
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Substitution: An effective control method for any hazardous chemical is substitution; a hazardous chemical is substituted with a less hazardous one. This is preferred especially if highly hazardous substances such as carcinogens are implicated, or those which may seriously impair human physiological systems. However, one must ensure that the substitute substance allows the elimination of the hazard posed by the previous substance.
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Engineering control (Closed system): If the option for substitution is not available easily, the personnel must be safe guarded against any exposure. A usually effective measure is to enclose the hazardous process or chemical. For example one must use sealed pipes to transfer toxic or highly flammable solvents and other liquids (especially the volatile ones) instead of pouring them in the open air. Exposures to vapours and gases need also be controlled and minimized if hazards are implicated in their use.
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Local exhaust ventilation: It may not always be possible to isolate experimental activities involving hazardous materials. In such a case solution must be sought through adequately designed local exhaust ventilation, which usually helps remove the contaminants at the source. A local exhaust ventilation system consists of a fume hood, ducts or pipes, a system to collect and separate the pollutants from the clean air, and an efficient fan to create the necessary suction force. Hazardous gases,fumes and dust collected from the vented air should, however, be treated before disposal. Inspection, proper maintenance, regular cleaning and changing of filters are essential to protect to protection against hazardous contaminants.
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General ventilation: Where it is difficult or impossible to prevent hazardous chemicals, fumes, dusts,mists or particles from entering the laboratory air at the source, general dilution ventilation can be installed so that the maximum airborne pollutant concentration does not exceed the TLV (see section VI) for the substance. At its best it should consist of an inflow of clean air and an outflow of exhaust forced by fans at placed at the right places. It can also be used with other preventive measures.
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Housekeeping: When working with dangerous chemicals, proper housekeeping is essential. Storage areas / stacks / cupboards must be well organized and kept in order. Maintenance of premises and equipment should also be planned. These tasks should be dedicated to persons/laboratory work groups. Periodic testing and repairing faulty equipment must also be ensured. The efficiency of housekeeping should be monitored with a suitable periodicity; this should involve the faculty-in-charge / students / staff associated with a laboratory.