Radon is a naturally occurring, chemically inert, radioactive gas. It is colorless, odorless, and tasteless. It is part of the uranium-238 decay series, the direct decay product of radium-226. Radon moves to the earth's surface through tiny openings and cracks in soil and rocks. High concentrations of radon can be found in soils derived from uranium-bearing rocks, such as pitchblende and some phosphates, granites, shales, and limestones. It may be found also in soils contaminated with certain types of industrial wastes, such as the by-products of uranium or phosphate mining, or from industries using uranium or radium.

In outdoor air, radon is diluted to such low concentrations that it is usually nothing to worry about. However, radon can accumulate inside an enclosed space, such as a home, posing a threat to people. The extents of radon in the United States, Massachusetts State and New York State are shown in Maps 31.1 through 31.3 where1:

• Zone 1: Counties that have a predicted average indoor radon screening level greater than 4pCi/L (picocuries per liter)—the highest potential.

• Zone 2: Counties that have a predicted average indoor radon screening level between 2 and 4pCi/L—moderate potential.

• Zone 3: Counties that have a predicted average indoor radon screening level less than 2pCi/L—low potential.

The known health effect associated with exposure to elevated levels of radon above the action or guidance level is an increased risk of developing lung cancer. The guideline levels for radon in existing homes are as follows:

• U.S. EPA (U.S. Environmental Protection Agency)2 4.0 pCi/L

• ICRP (International Commission on Radiation Protection)4 16.2 pCi/L

• WHO (World Health Organization)5 10.8 pCi/L

• NCRP (National Council on Radiation Protection)4 8.0 pCi/L

http://www.epa.gov/ radon/zonemap.html, February 2009.)"/>
MAP 31.1 United States map of radon zones. (Adapted from U.S. EPA, EPA Map of Radon Zones, EPA-402-F-93-013, U.S. Environmental Protection Agency, Washington, DC. Available at http://www.epa.gov/ radon/zonemap.html, February 2009.)
http://www.epa. gov/radon/zonemap.html, February 2009.)"/>
MAP 31.2 Massachusetts state map of radon zones. (Adapted from U.S. EPA, EPA Map of Radon Zones, EPA-402-F-93-013, U.S. Environmental Protection Agency, Washington, DC. Available at http://www.epa. gov/radon/zonemap.html, February 2009.)

Scientists estimate that about 20,000 lung cancer deaths a year in the United States may be attributed to radon.6 In general, the risk of developing lung cancer increases as the level of radon and the length of exposure increase. Radon can seep into the home in numerous ways—through dirt floors, cracks in concrete floors and walls, floor drains, sumps, joints, and tiny cracks or pores in some hollow-block walls. This seepage of gases into the house most often occurs when air pressure inside the house is lower than air pressure outside, or underneath, the house. In this case, cracks or other openings in the house allow radon-laden gas to be pulled inside.

Since radon is a colorless, odorless, and tasteless gas, the only way to detect its presence is to sample and analyze an area's air using a conventional radon measurement test. If the test reveals elevated radon levels, the homeowner will have to decide what steps to take to reduce the levels.7 The higher the level of radon present in a home, the more likely an active radon reduction system such as subslab depressurization (SSD)8 may be required. Lower radon levels may require only a passive reduction system, such as simple sealing.

Growing concern about the risks posed by indoor radon has underscored the need for dependable radon-resistant residential construction techniques. In response to this public health exposure, the U.S. EPA has developed and demonstrated a variety of methods that have been used to reduce radon levels in existing homes.2,8 Many of these methods could be applied during construction, involve less labor and financial investments, and provide greater homeowner satisfaction and safety than would a radon-reduction technique installed after the home is built and occupied.

This chapter is designed to provide homeowners and builders with an understanding of operating principles and installation details of the construction of a new radon-resistant home. This chapter should provide a basic understanding of the types of products and systems that are available and being used. In this way, the reader will be able to select the radon-resistant products and systems that will be best applicable to a particular situation.

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