 Typical domestic exposures average about 48 Bq/m3 indoors, though this varies widely, and 15 Bq/m3 outdoors.In the mining industry, the exposure is traditionally measured in "working level" (WL), and the cumulative exposure in "working level month" (WLM); 1 WL equals any combination of short-lived 222Rn daughters (218Po, 214Pb, 214Bi, and 214Po) in 1 liter of air that releases 1.3 × 105 MeV of potential alpha energy; 1 WL is equivalent to 2.08 × 10−5 joules per cubic meter of air (J/m3).The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m3).