The sensitizer which makes gelatin react to ultraviolet light is either potassium dichromate or ammonium dichromate. Similar risks apply to potassium dichromate, though it is generally considered the less toxic of the two. These materials must be handled with rubber gloves, with care taken to avoid even the slightest skin contact or breathing of the powder. Liquid solutions are not volatile, however. Ultraviolet light also causes skin cancer and cataracts in the eyes.
Carbon arcs are the most dangerous UV light sources.
Carbon monoxide is toxic because it displaces oxygen from the blood and deprives the brain and organs of oxygen. With any exposed UV light source, blackout darkroom-type curtains around the light source are strongly recommended. In addition, UV safety glasses should be worn to prevent any light leaks from damaging the eyes. From any manufacturer of UV light sources, it's useful to obtain test data on the actual spectrum their UV light sources emit, both the frequency range and the peak-energy frequencies. The fact is that no vacuum frame delivers a full vacuum throughout the entire exposure time, and so especially with large substrates there is always some loss of contact.