The effects of chemicals on the body are, at best, unpredictable. Factors to consider when attempting to determine a chemical exposure's impact include the dose; method of exposure; the receiver’s sensitivity to the chemical; and the additive, synergistic and potentiation effects, which I will explain later.
To protect workers from damaging chemical exposure, the person conducting the chemical hazard analysis must understand the specifics of the material being handled as well as the properties of materials (if any) that may be added to or mixed with the material. This includes common and expected effects of exposure, common methods of exposure, reactive properties of the material (including an analysis of conditions that will present a reaction), any flammable and combustible characteristics, biological effects and the effects created when the materials are mixed with others.
Many people know that mixing materials can be a very dangerous practice. Many do not know, however, that depending upon the materials that are mixed and the conditions that are present, the negative effects can be multiplied exponentially. Several chemical material mixing effects include:
The Additive Effect – When the additive effect occurs, chemicals that are combined add their individual toxic effects together, thus producing a biological effect that is the sum of the two individual effects. This can be compared to being exposed to double the dose of either of the chemicals independently. Additive effects typically take place when two chemicals have the same effect on the body, such as consuming of two different types of chemical depressants (i.e. narcotics and alcohol).
The Synergistic Effect – When the synergistic effect occurs, the exposure to two different toxic chemicals that have been mixed together will produce a more severe effect than simply doubling the dose of either of the chemicals alone. In this case, the effect of exposure is essentially multiplied rather than added together. The specific multiplication factors depend on the chemical properties involved in the mixture. For example, mixing ammonia and bleach creates deadly chlorine gas, which is much more hazardous than either ammonia or bleach alone.
Potentiation – When potentiation takes place, an exposure with no known chemical effect acts together with a known toxic material to produce a reaction that is much more potent than the known chemical and, in turn, creates a greater hazard. A common industrial application of the potentiation phenomenon is the effect produced when employees are exposed to high noise levels and ototoxins (chemicals such as fuel that can produce hearing loss) simultaneously. When this occurs, the permanent hearing threshold shifts are much more powerful than when exposed to noise alone. Thus the noise (with no toxic effect) acts with the known toxin to produce a more potent effect.
These effects must be thoroughly considered and comprehensively examined during chemical hazard analyses. Assessments should consider chemical use and the possibility and consequences of these effects. Without doing so, chemical safety is just a shot in the dark.
EHS Today guest blogger Jason Townsell was named the 2010 Future Leader in EHS. He works as an assistant safety manager/trainer for LA World Airports (LAWA) Airport Development Group.