MSHA's Occupational Illness and Injury Prevention Program Health Topic "Radon Daughter Measurement"

Radon is a radioactive gas associated with uranium mining and with several other underground mining industries. Radon daughters are fine solid particles which result from the radioactive decay of radon gas, and are hazardous because of the alpha radiation, or alpha particles, which they emit. When radon daughters are breathed and deposited in the lungs, the alpha radiation can harm sensitive lung tissue, and may cause lung cancer after years of exposure. The hazard of breathing air contaminated with radon daughters is especially serious because both radon gas and radon daughters are invisible and odorless. Beta and gamma radiation are also associated with the radioactive decay of radon gas, but ordinarily are not present in sufficient quantities to cause harm.

Radon gas diffuses into the mine atmosphere through rock and ground water. When rock such as uranium-bearing rock is broken, the surface area is greatly increased and emission of radon gas increases also. Agitation of ground water in underground mines can be a significant source of radon gas and the associated radon daughters.

Radon daughter particles have a tendency to attach themselvesto airborne particles such as dust, smoke, and water mist. These particles are fine enough to reach the deepest parts of the lungs when inhaled, and the alpha radiation emitted can do much damage.

For this reason, smoking is discouraged where radon gas is present. Regulations prohibit smoking in areas of a mine where monitoring of radon daughters is required.

The most effective control measure for radon gas and radon daughters is dilution and removal by means of ventilation. By quickly removing radon gas from work areas by ventilation, there will be less generation of radon daughters in the workplace. Primary air used for such ventilation should be as contaminant-free as possible of radon daughters. Special design practices are required for effectiveness to be assured.

Sampling for radon daughters involves the use of personal sampling pumps and special filters, through which air is drawn at a known rate. Radon daughters are collected on the filter, and the filter is evaluated by measurement of alpha radiation with a radiation counting device.

The use of personal respiratory protection against radon daughters must be limited to temporary situations where engineering controls have not been developed, or for maintenance and investigative work. For exposures up to 10 working levels (WL), proper filter-type respirators are available. Where concentrations of radon daughters exceed 10 WL, supplied-air respirators of other devices for protection against radon gas as well as radon daughters are required.