Ultraviolet radiation exposure criteria

During the past 25 years occupational health and safety guidelines, regulations and standards have evolved to protect workers and the general public from potentially hazardous exposure to ultraviolet radiation. A further goal has been to promote the safe design and use of suntanning devices, optical instruments, lamps, and laser products. From the gradually expanding knowledge of the biological effects of UVR exposure of the eye and skin, exposure limits have been slightly revised over the past two decades - by both national and international organisations. The general trend has been a convergence of differing limits. The greatest divergence in guidelines and standards has occurred where the biological effects are least understood or are simply controversial. Philosophical differences in the level of protection have played a role, since there are those who argue that UVR exposure offers more benefit than is accepted by all. The earliest guidelines were limited to UVR from low-pressure mercury lamps used in germicidal applications in the 1940s. By 1972 a North-American (ACGIH) guideline based upon an envelope action spectrum had appeared. The International Non-Ionizing Radiation Committee (INIRC) of the International Radiation Protection Association (IRPA) proposed similar guidelines in 1985 and these were revised based upon newer data a few years later. After an extensive review of the IRPA/INIRC guidelines, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) revalidated and endorsed those limits. Although these guidelines were based firstly on preventing any acute effects, they have also been analysed to show that the risk is extremely small, or undectable, for delayed effects for persons exposed below these recommended limits. The limits are approximately one-third of an MED (for fair skin) in any eight-hour period. At this level, detectable molecular damage appears to be fully repaired. Further refinement is still called for. For example, the maximal dose integration time is being debated, and it is not clear what could happen if human cells are exposed 24 h per day and not allowed the normal 'rest period' overnight.