The two most common radon testing devices are the charcoal canister and the alpha-check detector. Alpha-check detectors are ideal for making long-term measurements but are not suited for quick results (Lafavore 1987). A charcoal-adsorbent detector is the most practical approach for most. This test method is low-cost; the price for a single unit ranges from $10 to 50 (Cohen 1987). However, a disadvantage of charcoal is its sensitivity to temperature and humidity.
Charcoal-adsorbent detectors consist of granules of activated charcoal that adsorb gases (including radon) to which they are exposed. When the charcoal is exposed long enough to become saturated, the canister is resealed and shipped back to a laboratory where the radioactivity is measured. The laboratory calculates the level of radon to which the device was exposed.
Ideally, testing should be done in the late fall or early spring when the house is closed and the heating system is not turned on. Less natural ventilation does not dilute the radon concentrations at these times. The next best times are during winter months. Detectors that measure for three days or less require a closed-house procedure to start at least twelve hours before the test.
The detector should be placed in the lowest finished space in a spot where it is not disturbed. If the house has a basement, it should be placed there. The detector should be kept away from any sources of air movement, such as fire places and heating vents. To avoid the diluting effect of floor drafts, the tester should place the detector at least 20 in above the floor. The recommended exposure time for a radon detector is one to seven days.
The EPA recommends 4 pCi/l as the maximum acceptable indoor radon level. When the radon levels in a home range between 4 and 20 pCi/l, homeowners should take actions to reduce the air level within one to two years. If the level is between 20 and 200 pCi/l, action should be taken within several months. A reading above 200 pCi should be promptly reported and confirmed by the state department of environmental protection or department of public health.
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