Ultra-violet Radiation
Ultraviolet (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. Some of these sources can emit levels of UV that would lead to an over exposure in a matter of seconds. In workshops etc. arc welding generates high levels of UV radiation, which could lead to an over exposure in a matter of seconds.
Due to the potential hazard, where it is reasonably practicable, engineering control measures must be implemented to protect users and other from over exposure to UV radiation. In some cases, e.g. the operator of an arc welder, there may need to be reliance on procedures and personal protective equipment visors, gloves etc.
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. Click here for more information. 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 UV-A radiation can lead to the formation of cataracts.
As part of the risk assessment for UV sources, there should be a comparison between the potential exposure from the UV sources with the relevant exposure limit value (ELV). If the UV source is accessible, it is often most useful to understand the time it would take to exceed an ELV during exposure to the UV radiation. It may be that the manufacturer can provide this information, but if not, you should contact the University RPO for guidance.
The outcome of this assessment will help determine the control measures required. E.g if the ELV can be exceeded very quickly, robust engineering controls (e.g. interlocked enclosure) will be required.
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.
If it is not reasonably practicable to enclose a UV source, and this is justified in the risk assessment, the following procedures must be adhered to:
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.
UV Transilluminators.
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.
UV Crosslinkers.
• NEVER use a UV Crosslinkers which does not have a door safety interlock.
Arc Welding.
• ALWAYS shield other persons from the arc radiation.
• The operator must ALWAYS wear protective equipment, i.e. visors, gloves etc.