Been here? Until recenlty, there was no smoking inside the Duckering building where
I work, so the students who smoke stood outside the entrance doors,
just outside my window. Several times each day I'd make my way through
the "smoking sentinels." They were there when the temperature
is 35 below zero, and when the mosquitoes were buzzing. The risk of acute
frostbite and chronic tobacco-smoke induced cancer is "acceptable"
to them, or at least more acceptable than the alternative - surviving
nicotine withdrawal.
What's acceptable to you? If you are like me, it is zero, at
least from tobacco. (Don't tell me about the carcinogens in coffee,
though.) So what is an acceptable cancer risk to the public? Do
we take the 30% of the public that smoke and the 70% that don't
and somehow average them?
Earlier we demonstrated with the slope factor that we can always
calculate a risk of cancer from a chemical, if it caused cancer
at any level in laboratory animals. We will spend a lot more time
on this in a few weeks, because it arises often in dealing with
the public on risk related issues. But for now you need a number
and I will give you one - actually a range of numbers.
The EPA has identified the acceptable risk for superfund cleanups
as between 1 x 10 -4 to 1 x
10 -6, that is a one-in-ten-thousand
chance of developing cancer to a one-in-a-million chance. So for
the purposes of superfund funding, a site that causes a cancer
risk of more than 1 x 10 -4
is in a good position to get funding. A site that causes cancer
risks of less than 1 x 10 -6
probably will not get funding.
How about risks between 10 -4
and 10 -6? The EPA holds that
risks greater than 10 -4 might
not be cleaned up (with superfund money), either, unless there
are other mitigating factors, such as special ecological risks
or "other mitigating site-specific factors." As a practical
matter, the risks calculated are very conservative. The real risks
are typically less than you have calculated, often a lot less,
and may be zero. Also, real life situations are very complex,
or can be as complex as the budgets of the people who are investigating
them. When confronted with a risk in that acceptable range, one
would certainly "sharpen their pencil," and carefully
examine all the data and assumptions.
But engineers can't design things without numbers, so risks that
are greater than -4 are "considered
unacceptable," risks less than 10 -6
are "considered acceptable" and risks between 10
-4and 10 -6
are "considered in the acceptable range." If you are
asked who is the doer of the passive voice phrases above, the
answer is "the EPA. "
Is a risk of 1.6 x -7 considered
acceptable, unacceptable or in the a acceptable range
