- UV is the electromagnetic radiation covering the range 100 to 400 nm. It is commonly divided into 3 ranges of varying wavelength:
- UV-A 315-400 nm
- UV-B 280-315 nm
- UV-C 100-280 nm
The direct potential radiation hazard to health arises from UV with wavelengths greater than 180 nm. UV at lower wavelength is readily absorbed in air and only exists in a vacuum. Generally the shorter the wavelength the more biologically damaging is the UV radiation. UV-A is the least damaging (longest wavelength) form of UV and reaches the earth from the sun in great quantities. While UV-B exposure can be very harmful, stratospheric oxygen and ozone absorbs 97-99% of the sun’s light with wavelengths between 150 and 300 nm. UV-C is almost never observed in nature because it is completely absorbed by the atmosphere. However some equipment can generate concentrated UV radiation in all the spectral regions that if used without appropriate shielding can cause injury after only a few seconds of exposure.
There are several common sources of UV radiation in laboratories including germicidal lamps in biological safety cabinets, nucleic acid trans-illumination boxes and nucleic acid cross linkers activated by UV radiation.
In workshops etc. arc welding generates high levels of UV radiation. Curtains etc. must be used to shield non-operators. It is not possible to protect the arc weld operator other than by use of appropriate protective equipment – visors, gloves etc.
Hazards associated with exposure to UV radiation.
An unfortunate property of UV radiation is that there are no immediate warning symptoms to indicate overexposure. Symptoms of exposure including varying degrees of erythema (sunburn) or photokeratitis (welder’s flash) typically appear hours after exposure has occurred.
Skin injury by UV.
UV radiation can initiate a photochemical reaction called erythema within exposed skin. Certain individuals have abnormal skin responses to UV exposure (i.e. photosensitivity) because of genetic, metabolic or other abnormalities. Effects are exaggerated for skin photosensitised by a variety of chemical agents including birth control pills, tetracycline, sulphathiozole, cyclamates, antidepressants, coal tar distillates found in antidandruff shampoos, line oil, some cosmetics and certain foods (e.g. celery root). Chronic skin exposure to UV radiation has been linked to premature skin aging, wrinkles and skin cancer.
Eye injury by UV.
UV radiation exposure can injure the cornea, the outer protective coating of the eye. Photokeratitis is a painful inflammation of the eye caused by UV radiation-induced lesions on the cornea. Symptoms include a sensation of sand in the eye that may last up to two days. Chronic exposure to acute high-energy UV radiation can lead to the formation of cataracts.
UV safety and risk assessments
The following guidance will assist carrying out a risk assessment for work involving UV radiation.
• Determine the type of UV source (e.g. UV-A, UV-B or UV-C). This can be obtained from the manufacturer or it may be listed on the equipment. The type of UV determines the type of risk (e.g. skin, eye, etc).
• Determine the intensity of the source. Many UV bulb suppliers provide the bulb intensity in μW.cm-2 at a specific distance.
• Determine the exposure duration (hours per week or minutes per week).
• Compare the intensity and exposure duration with threshold limit values for skin and eye exposure. For UV-A (315 – 400 nm), total irradiation incident upon the unprotected eye should not exceed 1.0 mW.cm-2 for periods greater than 103 seconds.
• Identify suitable controls e.g.
o Shields, e.g. UV-opaque Perspex polycarbonate, blinds, curtains etc.
o Protective equipment e.g. lab coat, protective gloves,
o UV-opaque eye / full face shields. Ordinary prescription glasses may not block all UV radiation. UV certified goggles and safety glasses will protect the eyes, but it is common for lab workers to suffer facial burns in the areas not covered by goggles and glasses.
o Label equipment. Any equipment that emits UV radiation must be conspicuously labelled with a caution label e.g.
UV RADIATION HAZARD
USE ONLY WITH SHIELDING IN PLACE
PROTECT EYES AND SKIN FROM EXPOSURE TO UV LIGHT
- Consider use of warning lights to show when equipment is energised.
- Where sources are used which emit UV radiation of less than 242 nm, there must be adequate ventilation because of the hazard of ozone production. An extractor system may be required in some cases.
DO’s and DON’Ts
- NEVER allow the skin or eyes to be exposed to UV radiation sources.
- DO wear a fully buttoned lab coat, full leg covering and closed top shoes.
- DO be vigilant to prevent gaps in protective clothing that commonly occur around the neck and wrist areas.
- DO wear disposable nitrile gloves to protect exposed skin on the hands. Ensure wrists and forearms are covered between the tops of gloves and the bottom of the lab coat sleeves.
Biological Safety Cabinets and Germicidal Lamps.
NEVER work in a biological safety cabinet while a germicidal lamp is on.
- Germicidal lamps emit UV-C and typically the effective irradiance from a 15W germicidal strip lamp is 600 μW.cm-2 at 200nm and 40 μW.cm-2 at 1m.
- Lamps of this type must only be used inside closed cabinets with interlocked doors. The paint near these fixtures must not be reflective, and the cabinet must be constructed of suitable materials.
NB UV lamps are not recommended as they are no longer considered an effective sterilising method. Current standard BS EN 12469 references that UV lamps are not recommended for use in MSCs.
Portable UV sources.
ALWAYS mount portable UV sources in such a way that the radiation is directed away from the eyes.
These are used in biotechnology for visualisation of agarose and polyacrylamide gels. Samples are placed on the illumination window and illuminated by UV light. Devices operate at one of several wavelength bands depending on the type of sample. Standard wavelength bands are: 254nm, 312 nm and 365nm.
• NEVER use a transilluminator without its protective shield in place.
• ALWAYS keep shields clean and replace if damaged.
• NEVER use a UV Crosslinkers which does not have a door safety interlock.
• ALWAYS use curtains etc to shield other persons from the arc radiation.
• The operator must ALWAYS wear protective equipment, i.e. visors, gloves etc.