By the mid-1980s, scientists had already proven that indoor radon levels 10 to 100 times the average--an unacceptable amount--occurred in homes in various locations throughout the U.S. They also knew why levels could vary so greatly from one home to another and what could be done to lower levels that were deemed excessive. This knowledge had been gained during a broad effort by the research community beginning in the late 1970s and led to a large degree by the LBL radon group. Treating the problem as one of building science, LBL scientists spearheaded efforts to understand the physical processes accounting for radon entry and to analyze systematically the U.S. data from monitored homes.
The Indoor Environment Program's Efforts
These are still major interests of the Indoor Environment Program's Radon Group. Other IEP
groups are studying airborne chemicals, emissions from combustion appliances, control
techniques, and the energy performance of buildings. The program's basic approach is to
investigate the behavior of indoor pollutants and associated air and energy flows. This has led to
the recognition that the small pressure differences across the building shell that drive the overall
infiltration of outdoor air to the interior could be drawing radon-bearing air from the soil,
through the substructure, and into the occupied space.
The radon group's investigation of this process and of measures to reduce radon entry continues. One major effort has involved placing a pair of "small structures," essentially small basements, in the ground at a site in the Santa Cruz mountains and equipping them with an array of sensors for measuring pressure, radon concentration, and temperature in the surrounding soil. The purpose is to investigate, in long- or short-term controlled experiments, the dependence of radon entry rates on these parameters for various artificially imposed pressure differences between the structures' interiors and the outdoor air. In an-other effort, the group has expanded its development of computer models that simulate the transport of air carrying radon from the soil into homes. Increasingly, they use these models to evaluate the effectiveness of proposed control methods, particularly "subslab ventilation" techniques, which alter the pressure field and associated air flows between the soil and the building interior.
A third research area involves analyzing various types of radon field data gathered across the country, data that provide the basis for both understanding risks to humans from radon exposure and designing effective control strategies. A 1984 analysis yielded a tentative frequency distribution of indoor concentrations in U.S. homes averaging about 1.5 pCi/l and an estimate that about 7% of single-family houses have concentrations above 4 pCi/l, the action guideline set by the Environmental Protection Agency in 1986. This tentative distribution introduced some reality to the debate over radon and was confirmed in the early 1990s by a multimillion-dollar EPA survey.
Critical Evaluations
Since 1986, researchers familiar with the concentrations and behavior of radon, those at LBL
among them, have criticized the EPA's representation of the radon issue and its strategy for
control. One focus of criticism has been the EPA's use of short-term monitoring data, often
taken in basements, to indicate that 20 or 30% of homes exceeded the EPA guideline. In point of
fact, only the long-term average exposure is relevant to risk, and primary living space is where
most of the exposure occurs. The EPA has also tended to exaggerate risks, most recently
exposing itself to criticism for asserting that children in schools were at greater risk from radon
exposure than the adults.
A fundamental issue is whether the nation's control strategy ought to reduce radon levels everywhere or, instead or first, mount a concentrated effort to identify the homes with particularly high levels. For example, 50,000 to 100,000 homes are estimated to have annual average concentrations in primary living space of 20 pCi/l or more. This level causes an annual radiation exposure roughly equal to the occupational exposure limit (established for underground uranium miners, the group that provides most of the data for estimating the risk from radon exposure). Twenty years' occupancy of such a house would yield an added risk of lung cancer of about 1%, even among nonsmokers. This level of risk is very high compared with the risks estimated for other kinds of environmental exposures regulated by the EPA.
However, the average level of radon in homes is also estimated to cause risks at the 0.1% level for nonsmokers, larger than other known environmental risks, including radon outdoors. The result is that the EPA's regulatory effort has focused on near-average indoor exposures, engendering a conflict over the orientation of control strategies. The conflict is unlikely to be resolved without more careful evaluation of inherent risks in the indoor environment.
In 1992, I published an article called "A National Strategy for Indoor Radon" in Issues in Science and Technology (Fall 1992, pp. 33-40), explaining what had happened since the mid-1980s and proposing an alternative course. The article recommended a commitment to several near-term steps:
-Anthony Nero
Next issue: developing a methodology for identifying high-radon areas.
Anthony Nero
Indoor Environment Program
(510) 486-6377; (510) 486-6658 fax