Concept
Hazard substitution is a hazard control strategy in which a material or process is replaced with another that is less hazardous. Substitution is the second most effective of the five members of the hierarchy of hazard controls in protecting workers, after elimination. Substitution and elimination are most effective early in the design process, when they may be inexpensive and simple to implement, while for an existing process they may require major changes in equipment and procedures. The concept of prevention through design emphasizes integrating the more effective control methods such as elimination and substitution early in the design phase. Hazard substitutions can involve not only changing one chemical for another, but also using the same chemical in a less hazardous form. Substitutions can also be made to processes and equipment. In making a substitution, the hazards of the new material should be considered and monitored, so that a new hazard is not unwittingly introduced, causing "regrettable substitutions". Substitution can also fail as a strategy if the hazardous process or material is reintroduced at a later stage in the design or production phases, or if cost or quality concerns cause a substitution to not be adopted. Substitution of dangerous chemicalsA common substitution is to replace a toxic chemical with a less toxic one. Some examples include replacing the solvent benzene, a carcinogen, with toluene; switching from organic solvents to water-based detergents; and replacing paints containing lead with those containing non-leaded pigments. Dry cleaning can avoid the use of toxic perchloroethylene by using petroleum-based solvents, supercritical carbon dioxide, or wet cleaning techniques. Chemical substitutions are an example of green chemistry. Chemicals can also be substituted with a different form of the same chemical. In general, inhalation exposure to dusty powders can be reduced by using a slurry or suspension of particles in a liquid solvent instead of a dry powder, or substituting larger particles such as pellets or ingots.