Opinion ID: 1176318
Heading Depth: 2
Heading Rank: 4

Heading: Use of Working Levels

Text: Finally, petitioners contend that EFSC erred in measuring radon-222 concentrations in terms of working levels rather than picocuries per liter. As we stated in note 5 above, a curie is a measure of the number of radioactive disintegrations per second. To say that a radon-222 concentration is a certain number of picocuries per liter is to say that a liter of air contains an amount of radon-222 such that a certain number of radioactive disintegrations per second are occurring from the radon-222 in that liter of air. The health threat posed by radon-222, however, is not primarily from radon-222 itself but from the radioactive by-products, or daughters, of radon-222 decay. Radon-222 is a gas that is easily breathed in and out of the lungs. The radon daughters are solids that lodge in the lungs, where high-energy alpha particle radiation from the daughters can cause significant damage to the body. A working level is a measure of the alpha particle energy emitted by radon-222 daughters. As such, the working level in a house is considered to be a better measure of the health threat caused by radon-222 than is a measure of the radon-222 concentration itself. To translate a radon-222 concentration into a working level requires a correction for the degree of equilibrium between radon-222 and its daughters. Radioactive equilibrium is the condition in which a radioactive species and its successive radioactive products have attained such relative proportions that they all disintegrate at the same numerical rate and therefore maintain their proportions constant. Webster's Third New International Dictionary 1872 (1971). Only if radon-222 and its daughters are in perfect equilibrium will the OAR 345-50-035 threshold of 3 picocuries per liter of radon-222 equal the threshold of 0.0333 working levels. If, as is ordinarily the case in nature, radon-222 and its daughters are not in equilibrium, the working level of 3 picocuries per liter of radon will be less than 0.0333 working levels. Petitioners argue that because OAR 345-50-035 states that a radon-222 concentration of 3 picocuries per liter is appropriate for protection from radon-222 combined with its short-lived daughters, and because it is difficult to calculate the degree of equilibrium between radon-222 and its daughters, EFSC erred in determining the radioactivity of TWCA's waste by using working levels rather than picocuries per liter of radon-222. The rule, however, provides in the next sentence: Alternatively, this value [3 picocuries per liter] may be replaced by one-thirtieth (1/30) of a `working level.' Thus, the rule permits EFSC to use either picocuries per liter or working levels as the appropriate measure. Given the expert testimony from EFSC's consultant that a measurement expressed in working levels provides a better assessment of health risks than does a measurement expressed in curies  a point that petitioners did not dispute in theory  EFSC did not act improperly by choosing to use working levels to evaluate TWCA's waste. See ORS 183.482(8)(b).