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| Occupational hazards |
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| Hierarchy of hazard controls |
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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 thehierarchy of hazard controls in protecting workers, afterelimination.[1][2][3] 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.[1] The concept ofprevention through design emphasizes integrating the more effective control methods such as elimination and substitution early in the design phase.[4]
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,[3] causing "regrettable substitutions".[5] 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,[6] or if cost or quality concerns cause a substitution to not be adopted.[7]
A common substitution is to replace a toxic chemical with a less toxic one.[8] Some examples include replacing thesolventbenzene, acarcinogen, withtoluene; switching from organic solvents towater-baseddetergents; and replacing paints containinglead with those containing non-leaded pigments.[3]Dry cleaning can avoid the use of toxicperchloroethylene by usingpetroleum-based solvents,supercritical carbon dioxide, orwet cleaning techniques.[9] Chemical substitutions are an example ofgreen chemistry.[5]
Chemicals can also be substituted with a different form of the same chemical. In general, inhalation exposure todusty powders can be reduced by using aslurry orsuspension of particles in a liquid solvent instead of a dry powder,[10] or substituting larger particles such aspellets oringots.[3] Some chemicals, such asnanomaterials, often cannot be eliminated or substituted with conventional materials because their unique properties are necessary to the desired product or process.[10] However, it may be possible to choose properties of the nanoparticle such assize,shape,functionalization,surface charge,solubility,agglomeration, andaggregation state to improve their toxicological properties while retaining the desired functionality.[11]
In 2014, the U.S.National Academies released a recommended decision-making framework for chemical substitutions. The framework maintained health-related metrics used by previous frameworks, includingcarcinogenicity,mutagenicity,reproductive anddevelopmental toxicity,endocrine disruption,acute andchronic toxicity,dermal andeye irritation, and dermal and respiratorysensitization, andecotoxicity. It added an emphasis onassessing actual exposure rather than only the inherent hazards of the chemical itself, decision rules for resolving trade-offs among hazards, and consideration of novel data sources on hazards such assimulations. The assessment framework has 13 steps, many of which are unique, such as dedicated steps for scoping and problem formulation, assessingphysicochemical properties, broaderlife-cycle assessment, and research and innovation. The framework also provides guidance on tools and sources for scientific information.[12]
Hazards to workers can be reduced by limiting or replacing procedures that mayaerosolize toxic materials contained in the item. Examples include limiting agitation procedures such assonication, or by using a lower-temperature process inchemical reactors to minimize release of materials in exhaust.[13] Substituting a water-jet cutting process instead of mechanical sawing of a solid item also creates less dust.[14]
Equipment can also be substituted, for example using a self-retracting lifeline instead of a fixed rope forfall protection,[15] or packaging materials in smaller containers to prevent lifting injuries.[16]Health effects from noise can be controlled by purchasing or renting less noisy equipment. This topic has been the subject of severalBuy Quiet campaigns, and theNIOSH Power Tools Database contains data on sound power, pressure, and vibration levels of many power tools.[17][18]
A regrettable substitution occurs when a material or process believed to be less hazardous turns out to have an unexpected hazard. One well-known example occurred whendichloromethane was phased out as abrake cleaner due to its environmental effects, but its replacementn-hexane was subsequently found to beneurotoxic.[5][12] Often the substances being replaced have well-studied hazards, but the alternatives may have little or no toxicity data, making alternatives assessments difficult.[5] Often, chemicals with no toxicity data are considered preferable since they do not prompt such concerns as aCalifornia Proposition 65 warning.[19]
Another type of regrettable substitution involves shifting the burden of a hazard to another party. One example is that the potent neurotoxinacrylamide can be replaced with the saferN-vinyl formamide, but the synthesis of the latter requires use of the highly toxichydrogen cyanide, increasing the hazards to workers in the manufacturing firm. In performing analternatives assessment, including the effects over the entireproduct lifecycle as part of alife-cycle assessment can mitigate this.[12]
