An object is falling from an apartment balcony. Will it hurt you?
Time for some quick thinking. What is it, how big is it, and is it going to hit you?
Well, it's a huge concrete flower pot, and if it hits you, it will kill you. But not to worry—you're on the other side of the street!
Welcome to the art of risk assessment!
Converted to the language of scientific risk assessment, you took three steps to make your final judgment:
- You identified a hazard.
- You assessed your potential exposure to the hazard.
- You determined that you would not be exposed to the hazard presented by the falling flower pot and weren't at any risk.
Hazard refers to the inherent properties of a substance that make it capable of causing harm to human health or the environment.
Exposure describes both the amount of, and the frequency with which, a chemical substance reaches a person, group of people or the environment.
Risk is the possibility of a harmful event arising from exposure to a chemical or physical agent, for example, under specific conditions.
There are hazards all around us. But a hazard doesn't become a risk unless you are exposed to it. And, if you are exposed, the exposure has to be at a level that might do harm; it makes a difference if it's the flower pot or just the flower that falls off the apartment balcony and hits you. Making the distinction is important to our well-being, because, as The Reporter's Environmental Handbook states, "…the risks that make people angry or frightened may or may not be the risks that endanger their health and environment." *
Take the subject of chemicals in the environment. In the 15th Century, a doctor with the name Theophrastus Phillippus Aureolus Bombastus von Hohenheim, more comfortably known as Paracelsus, theorized that it wasn't the balance of "humours" inside the body that made people sick or well, but agents outside the body that got in and caused good or harm. He learned that the same chemical could do both—a little could make a person better, but a lot could kill. His discoveries have been distilled into the toxicologist's axiom: "the dose makes the poison."
Any chemical that gets into our bodies, even common table salt (sodium chloride) can become a risk if the dose we ingest is large enough. That's where science and government team up to help.
From studies of human data, or environmental data, or from laboratory studies on animals, scientists can usually calculate the point at which a hazard might become a risk. For chemicals, regulatory agencies set exposure limits, using scientific data to determine a level where no effects have been observed and then dividing by ten, a hundred, a thousand, or more, to build in a large margin of safety.
* Bernadette West, Peter Sandman, Michael R. Greenberg, The Reporter's Environmental Handbook (New Jersey: Rutgers University Press,1994), p. 21.