Working level radon concentration

Working level month (WLM) An exposure ot I WLM can be taken to be received by a person working in a Radon daughter concentration of 1 WL for 170 hours. 

Working Level Month (WLM)—A unit of exposure to radon daughters corresponding to the product of the radon daughter concentration in Working Level (WL) and the exposure time in nominal months (1 nominal month =170 hours). Inhalation of air with a concentration of 1 WL of radon daughters for 170 working hours results in an exposure of 1 WLM. 

MeV. WL-R = 100% x WL/radon concentrations (pCi/1). The dose conversion factor of 0.7 rad/working level month (WLM) (Harley and Pasternack, 1982) was used to calculate the mean absorbed dose to the epithelial cells and a quality factor (OF) of 20 was applied to convert the absorbed dose to dose equivalent rate. For example, from the average value of (WL) obtained from the arithmetic mean radon concentrations measured in the living area during winter and summer in South Carolina (Table I), the calculated dose equivalent rate is 4.1 rem/yr, e.g.,... 

A survey of the radon concentrations in a representative sample of more than 2000 dwellings in the UK has been completed and provisional results are now available. On average, concentrations are 29% lower in bedrooms than in living areas. The mean radon concentration weighted for room occupancy is 22 Bq m 3. Assuming an equilibrium factor of 0.35 and a mean occupancy of 75%, the mean annual exposure in UK homes is assessed as 0.08 Working Level Months (WLM) and the mean annual effective dose equivalent as 0.43 mSv. 

An equilibrium factor of 0.35, derived from measurements made during the local surveys, has been assumed to typify conditions in UK dwellings. This value has been used to convert the average radon concentrations measured in the national survey to potential alpha-energy concentration of radon decay-products. On average, persons in the UK spend 75% of their time in their homes and 15% of their time elsewhere indoors (Brown, 1983). The occupancy factor of 0.75, together with an equilibrium factor of 0.35, results in an annual exposure of 1.3 10"5 J h m"3 (0.0037 Working Level Months,... 

Aerosol concentrations, radon, and PAEC (in Working Levels) clearly peak in early hours after sunrise and at about the time of morning human use of the building which is coincident with the outdoor peak in radon and fine aerosols due to their overnight accumulation near ground level under local temperature inversions. ... 

Measures to reduce radon concentrations have been studied in an old house in which the radon decay-product concentration initially exceeded 0.3 Working Level (WL). Some of the measures were only partially successful. Installation of a concrete floor, designed to prevent ingress of radon in soil gas, reduced the radon decay-product concentration below 0.1 WL, but radon continued to enter the house through pores in an internal wall of primitive construction that descended to the foundations. Radon flow was driven by the small pressure difference between indoor air and soil gas. An under-floor suction system effected a satisfactory remedy and maintained the concentration of radon decay products below 0.03 WL. 

Before standards for indoor exposure to radon can be formally established, work is necessary to determine whether remedies are feasible and what is likely to be involved. Meanwhile, the Royal Commission on Environmental Pollution (RCEP) in the UK has considered standards for indoor exposure to radon decay products (RCEP, 1984). For existing dwellings, the RCEP has recommended an action level of 25 mSv in a year and that priority should be given to devising effective remedial measures. An effective dose equivalent of 25 mSv per year is taken to correspond to an average radon concentration of about 900 Bq m 3 or an average radon decay-product concentration of about 120 mWL, with the assumption of an equilibrium factor of 0.5 and an occupancy factor of 0.83. 

Continuous measurements of the potential alpha energy concentration of the radon decay products were made with a Continuous Working Level Monitor (WLM-300) (EDA Instruments Inc., Toronto). 

This concentration is equivalent to a partial pressure of radon of 6.6x10 atmospheres. Yet this value is an elevated radon concentration. If all of the decay products formed by the decay of the radon remain in the air, then there would also be 10 pCi/1 of Po-218, Pb-214, etc. Such a mixture would be said to be in secular equilibrium. From the monitoring of uranium mines, an equilibrium mixture of these decay products at 100 pCi/1 is called a working level (WL). Thus, a 10 pCi/1 equilibrium mixture represents 0.1 working level. 

Radon is present in the air and soil. It can leak into the indoor environment through dirt floors, cracks in walls and floors, drains, joints, and water seeping through walls. Radon can be measured by using charcoal containers, alpha-track detectors, and electronic monitors. Results of the measurement of radon decay products and the concentration of radon gas are reported as working levels (WL) and picocuries per liter (pCi/L), respectively. The continuous exposure level of 4 pCi/L or 0.02 WL has been used by USEPA and CDC as a guidance level for further testing and remedial action [33]. 

In the uranium mining industry, the Working Level (WL) is defined as a concentration of decay products having PAEC equal to that of decay products in equilibrium with 100 pCi l-1 (3.7 x 103 Bq m-3) of radon. The Working Level Month (WLM) is defined as exposure to decay products equivalent to 1 WL for 170 h, this being the nominal number of hours worked per month in a mine. The WLM is still used in discussions of the epidemiology of lung cancer in relation to exposure to radon and its decay products. 

D22.05 D6327-98 Standard Test Method for Determination of Radon Decay Product Concentration and Working Level in Indoor Atmospheres by Active Sampling on a Filter... 

An additional unit of measurement used to describe human exposure to radon and radon progeny is the Working Level Month (WLM), which expresses both the intensity and duration of exposure. One WLM is defined as the exposure of a person to radon progeny at a concentration of 1.0 WL for a period of 1 working month (WM). A working month is assumed to be 170 hours. The S.l. unit for WLM is joule- hour per cubic meter of air (J-h/m ) 1 WLM is equal to 3.6x10 J-h/m. ... 

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