Long wave ultraviolet (also known as black light or UV-A) emissions typically range from 320nm to 400nm in the electromagnetic spectrum. Although long wave UV emissions are known to be relatively safe compared to other ultraviolet emissions, it is necessary for all operators and supervisors to observe certain safety precautions when working with high-intensity UV-A sources.

Personnel using long wave UV lamps should avoid looking directly at the sources, as this can cause fluorescence of the eyeball. This would result in lowering the ability of the user to detect the fluores­cent response. The filter used with UV-A sources, either as an integral part of the bulb / tube or as a separate component, should always be maintained in good condition and free from cracks, as radia­tion at wavelengths below 320nm can be very dangerous.

It is a good practice not to shine UV-A sources onto exposed skin, especially when the user is taking certain medications which produce increased photosensitivity to UV. Such exposure can cause skin irritation. Users should wear long-sleeve, nonfluorescent clothing and nonphotochromic goggles when performing inspection. The goggles should be made of clear optical material (not tinted) and possess UV-blocking capabilities; the transmission in the long wave UV region should be better than 10-4.

The threshold limit values published by the American Conference of Governmental Industrial Hygienists (ACGIH) for occupational exposure to UV-A radiation states that the total irradiance incident upon the unprotected eyes should not exceed 1 mW/cm2 for periods greater than 1,000 sec­onds (approximately 16 minutes). For exposure times less than 1,000 seconds, the total UV-A dosage should not exceed l Joule/cm2 (Joule = watts x seconds).

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