Direct light from lamps should not be visible and bounce (reflected) light should be minimized and avoided. Medium pressure UV lamps radiate harmful UV which can cause serious burns to skin and eyes. While thermal burns are felt immediately, UV burns are not felt for several hours. Short exposure to lamp radiation can cause severe burning of skin and eyes. UV burn of the eyes affects the cornea and takes several days to heal. UV burn is identical to "Welder's burn" and will feel like sand in the eyes that cannot be washed out. The discomfort is transitory. Extreme caution must be taken - high power UV radiation can cause blindness.

Limited exposure to UV radiation will evoke erythema on normal skin. Such erythema is transitory and will not produce blistering, nor tanning, as only a small amount of radiation penetrates the Malpighian layer. Extreme caution must be taken since, high power UV radiation can cause severe burns to the skin.

Handling UV lamps

The carton should be opened fully so lamp can be lifted out of packaging with no twisting or pulling. Unpacking should take place in an area large enough to eliminate the possibility of inadvertently striking lamp against walls, pillars, pipes, beams or press machinery.

Lamp must be wiped with alcohol before placing in service. Bare skin contact with the quartz envelope must be avoided. Compounds from the skin when heated on lamps operating at 600 to 850C will form permanent etching (devitrification) on the quartz surface decreasing UV energy transmission. A contaminated lamp eventually will overheat causing premature failure.

Ozone Safety

Tri-atomic oxygen or ozone (O3) is the only byproduct of the UV lamp. It is formed by oxygen being exposed to 254nm wavelengths of UV energy. Ozone formation can be eliminated by using ozone-free quartz lamps. Certain dioxides which absorb the ozone producing wavelengths are added to the quartz of these lamps.

Ozone-free and pure fused quartz lamps are interchangeable. Ozone-free lamp usage may affect cure speeds if ink or coating formulation is designed to utilize the absorbed wavelengths.

A nitrogen atmosphere in a processor also eliminates ozone production by eliminating oxygen. Lower power lamps may be used in a nitrogen atmosphere; however, the cost of nitrogen will probably offset any operating cost savings attained.

Ozone can be effectively eliminated in the processing area by exhausting air from the cooling system of the UV processor to outside the building. Such exhausting involves no danger as the hot gas is very unstable and breaks down to oxygen rapidly in ducting. Neither a nitrogen atmosphere or ozone-free lamps eliminate the cooling system required by lamps and related UV processor components.

Short Arc Safety

Short arc lamps operate at considerably high pressures up to fifty atmospheres. Mercury-xenon short arc lamps emit large amounts of ultraviolet radiation which can be extremely harmful to eyes and skin. No short arc lamps should ever be operated outside of an approved enclosure at any time. Due to their high power and relatively small size, forced cooling parallel to the axis of the lamp is required. The lamp end fittings must be kept below 225 degrees centigrade.

When a short arc lamp is shut off, forced air cooling is recommended until the quartz envelope of the bulb falls below 60 degrees centigrade. Short arc lamps operate at high electrical currents. It is essential that the lamp mounting connectors of the enclosures are inspected regularly to avoid high resistance. Overheating of the lamp fittings will cause premature lamp failure.

All short arc lamps must be installed with the correct polarity orientation. Reversed polarity will cause immediate lamp electrode deterioration leading to premature lamp failure. Lamps are shipped in a protective plastic sleeve. With one end removed, the lamp can be installed while the protective sleeve is still on. With the lamp being installed, the sleeve is then removed prior to lamp operation. Protective face and hand protection should be worn while installing or removing short arc lamps.