Measurements of eye damaging radiation in rabbits and in monkeys show a peak sensitivity at 270 nm. and a minimal dose for damage of about 4-5 mJ/cm2. Ultraviolet radiation damage is gradually repaired depending on degree of damage. Damage from a minimal dose should be repaired within 24 hours.
The PMA2100 radiometer indicates how long a worker may remain at the measured position before reaching the threshold limit value (TLV) proposed by the ACGIH The TLV of 3 mJ/cm2 in an 8 hour period has been chosen by the ACGIH as one which can be tolerated, even if repeated every work day, without causing any long term effect.
The meter reading should be of the highest intensity at a site. The worker’s natural avoidance of the usually bright UVR light source, and the contraction of the pupil provide additional safety from the measured UVR when it emanates from a visually bright source. Even without these normally occurring safety enhancements not exceeding the TLV will provide adequate protection.
The TLV for UV radiation specified by ACGIH apply to sources which subtend an angle less than 80°. Sources which subtend a greater angle need to be measured only over an angle of 80°.
The instantaneous value indicates how long an exposure at the intensity being measured is required to produce a dose of 3 mJ/cm2. The PMA can also be set to continuously monitor UV and sound an alarm when the preset dose or irradiance level is reached.