UV Lamp Handling.

Fused quartz (Silicon di-oxide, SiO2) with a high melting point and excellent UV transmissivity is used in fabrication of UV processor lamps. A 22 x 25 mm diameter tube with wall thickness of 1.0 to 1.5 mm used with tungsten electrodes sealed into each end is typical. Lamps are manufactured from 1" to 180¡± arc length. Quartz is very fragile and special cushioned packaging is utilized for safe transportation. Upon receiving new lamps the carton should be opened fully so the lamp can be lifted out of the 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 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 600o to 850o C will form permanent etching (devitrification) on the quartz surface, decreasing UV energy transmission. A contaminated lamp eventually will overheat causing premature failure.

UV Safety

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.

Thermal Safety.

Infrared energy, an inherent product of the arc utilized to create UV energy in UV processors, can cause overheating of processor components when adequate safeguards are not incorporated into the UV processor design and application. Cooled heat sinks should provide protection to the press, conveyor, and other process components in or near the UV processor. The cooling system should be carefully designed and properly maintained. In air-cooled systems, filters must be properly cleaned or replaced on a maintenance schedule related to powder, dust, and dirt conditions where the UV processor is operating. Halon #1211 fire extinguishers are to be used in the event of fire. CO2 fire extinguishers with dry chemical or water are NOT recommended. If a fire occurs, all residue of damaged substrate should be removed from curing area. Soot and ash must be cleaned from lamps and reflectors before re-start. Investigation to determine the malfunction causing the fire is most important. Correction must be made to eliminate re-occurrence. UV processor electrical systems should be serviced only by qualified electricians.

Cooling:
To most, cooling of the lamp is usually perceived to be one of the least important factors in the function of the UV curing system, but in fact it is one of the most important. UV lamp is made of quartz because this is the only material that transmits UV-light and at the same time endures high temperatures of 6 to 800¡ÆC.

Each UV system was intended to function in a certain temperature range and when the temperature falls out of this range the lamps will degrade at a much faster rate. On many systems the blower has a baffle to regulate airflow to the UV lamp, hence regulating temperature. When this baffle is closed too much the lamp will tend to overheat, which is usually seen when the lamps become distorted in shape and end fillings and wire possibly showing signs of extreme heat. On the other hand when the baffle is open too much the lamp may be overcooled, this will show when the ends of the lamp turn dark black. Both of these conditions are detrimental to the life of the lamp.

SKIN safety
Longer UVA wavelengths emitted by black lights and general purpose high pressure mercury lamps are basically harmless. Although the hazard is not quite zero, it is generally quite negligible. The same is generally true of any UV-containing light that has passed through ordinary glass.

There is an exception: Some drugs photosensitize skin to ordinarily harmless quantities and wavelengths of UV. Ask your doctor or pharmacist.

Shorter UVA wavelengths cause suntanning. It is widely believed that UV suntanning is not completely safe no matter what you do. Possible ill effects include skin cancers and accelerated aging of the skin.

UVB is much worse, inherently irritating. The skin is designed to take small amounts of UVB and recover, but nothing is perfect here. You probably want to avoid any significant UVB exposure unless a physician recommends UVB exposure for medical purposes.

UVC is even worse, but less penetrating since it is easily absorbed. The outermost portion of human skin is made of dead cells. This layer sometimes gives partial protection from UVC, especially shorter wavelengths. However, don't count on this. UVC is quite damaging to living cells and has nasty burning effects.

EYE safety
UVA has one nasty effect on eyes, known as "nuclear cataracts". This is a permanent "tanning" of the lens of the eye. "Nuclear" refers to this occurring mainly in the center of the lens of the eye. You need heavy exposure to get this. Nuclear cataracts occur mainly among people who work outdoors. Although incandescent black lights emit wavelengths that cause nuclear cataracts, they are largely safe since you typically get less UV exposure from these than from sunlight. Even considering the fact that your pupils are wider under black light than under sunlight, there is so much less UV that it is safe to stare into the bulb from a few feet away for large amounts of time.

Fluorescent black lights are worse, but are usually comparable to sunlight when you are a couple feet away. Although I have yet to hear of eye damage blamed on reasonable use of black lights, those who are around them a lot may want UV blocking eyewear.

Persons who have had cataract surgery need extra protection, since the lens of the eye largely absorbs UV. The retina does not like strong exposure to UV. It should be noted that UVA-related eye damage involves a process with at least two steps. The first step (excitation of tryptophan or related molecules) normally reverses itself. Damage requires excited molecules to receive additional UV before they de-excite. This means that UVA eye damage is not linearly proportional to the intensity of exposure, although it may be proportional to the duration of exposure of a given intensity.

I have yet to see data indicating clearly what is and is not safe. However, nuclear cataracts are most common in people who work outdoors in sunny areas. In case of doubt, use UV blocking eyewear. Cheaper amber and yellow sunglasses do actually work - I have tested them. Sunglass lenses made of real glass and green in color attenuate UV a fair amount. Clear, blue, purple, or pink glasses may not work, even if they are claimed to work. I saw one pair of clear glasses with a sticker claiming "100 percent UV blocking" which let through more UV than window glass did.

UVB is worse on eyes than UVA, and can burn the cornea and the conjunctiva. UVC is especially burning to the conjunctiva. Please beware that symptoms are delayed considerably from exposure. Symptoms typically begin a few minutes after exposure and gradually increase for at least a half an hour, often an hour to a few hours after exposure. If you have been exposed and any symptoms begin, promptly seek emergency medical care to minimize damage.