Ultraviolet (UV) radiation is electromagnetic energy with a wavelength just shorter than that of visible light. UV energy stimulates vitamin D production in our bodies and is a treatment for psoriasis, but can also cause skin cancer, sunburns and cataracts.
Sources of UV Radiation in Labs
Germicidal lamps emit radiation almost exclusively in the far-UV range of 254 nm. They are commonly used in biological safety cabinets and are not to be relied on as the only method of decontamination.
The UV light box is another UV source in use in laboratories. This instrument is a box with a glass top and a UV lamp inside. Some units have multiple lamps that allow a choice of wavelength.
Most of these instruments are stationary, but a few are hand-held types that carry the same hazards as the stationary models. Nucleic acid (DNA or RNA) which has been stained with the chemical Ethidium Bromide, lights up when exposed to UV light.
The Journal of Chemical Health & Safety published an assessment of UV exposure from transilluminator light boxes (PDF) that explains hazards, controls and some common mistakes.
A UV-Crosslinker is used to "cross-link" or covalently attach nucleic acid to a surface or membrane following Southern blotting, Northern blotting, dot blotting, and Colony/Plaque lifts. Since the DNA will be used in place, a 254 nm wavelength is used to maximize adherence.
Some Devices Emitting UV Radiation
- Bactericidal lamps
- Black light lamps
- Carbon, xenon and other arcs
- Dental polymerizing equipment
- Fluorescence equipment
- Hydrogen and deuterium lamps
- Ultraviolet nail curing lamps
- Mercury lamps
- Phototherapy lamps
- Printing ink polymerizing equipment
- Welding equipment
- Trans-illuminator light boxes
UV radiation has shorter wavelengths (higher frequencies) compared to visible light but have longer wavelengths (lower frequencies) compared to X-rays. UV radiation is divided into three wavelength ranges.
Some health effects of exposure to UV light are familiar to anyone who has had a sunburn; however, the UV energy levels around certain UV equipment greatly exceeds the levels found in nature. Health effects vary with the duration of exposure as well as the intensity and wavelength of the energy.
The shortwave UV radiation (UV-C) poses the maximum risk. The sun emits UV-C but it is absorbed in the ozone layer of the atmosphere before reaching the earth. Some man-made UV sources also emit UV-C. However, the regulations concerning such sources restrict the UV-C intensity to a minimal level and may have requirements to install special guards or shields and interlocks to prevent exposure to the UV. Bypassing shields can expose personnel to acutely dangerous levels of UV-C radiation.
The medium wave UV (UV-B) causes skin burns, erythema (reddening of the skin) and darkening of the skin. Prolonged exposures increase the risk of skin cancer.
Longwave UV radiation (UV-A) accounts for up to 95% of the UV radiation that reaches the earth's surface. Although UV-A is less intense than UV-B, it is more prevalent and can penetrate deeper into the skin layers, affecting the connective tissue and blood vessels, which results in premature aging.
Acute Health Effects
Type - UV-A
Wavelength - 315-400 nm
Acute Health Effects -
- darkening of the skin
Type - UV-B
Wavelength - 280-315 nm
Acute Health Effects -
- reddening of the skin, blistering of the skin, first or second degree burns, darkening of the skin
- Photokeritisis (welders flash) is inflammation of the cornea: symptoms include watery eyes and blurry vision, itchiness and pain
- photoconjunctivitis is inflammation of the membrane on the outside of the eye: symptoms include watery discharge and discomfort
Type - UV-C
Wavelength - 100-280 nm
Acute Health Effects -
- In humans, UVC is absorbed in the outer dead layers of the epidermis.
- Photokeritisis (welders flash)
- UVC injuries may clear within a day or two, but can be extremely painful
Chronic Health Effects
Effect on the skin
Long-term exposure to UVR can cause thickening of the skin, changes in cells which may cause fibrous tissue and blood vessels leading to premature skin aging, photodermatoses, and actinic keratoses. Long-term exposure may also cause freckling, premature wrinkling, and permanent "sun spots," melanoma and other skin cancers.
Certain chemicals and medications act as photosensitizing agents and enhance the effect of UV radiation form sunlight or other sources. Such agents include:
- thiazide diuretics (drugs which cause excessive urine production)
- thiazine tranquilizers
- drugs used in the treatment of high blood pressure
- certain antibiotics (tetracyclines, sulfonamides)
- various plants such as carrot, celery, dill, fig, lemon and some types of weeds
Effect on the eyes
The eyes are particularly sensitive to UV radiation. Even a short exposure of a few seconds can result in a painful, but temporary condition known as photokeratitis and conjunctivitis.
- Photokeratitis is a painful condition caused by the inflammation of the cornea of the eye. The eye waters and vision is blurred.
- Conjunctivitis is the inflammation of the conjunctiva (the membrane that covers the inside of the eyelids and the sclera, the white part of the eyeball); which becomes swollen and produces a watery discharge. It causes discomfort rather than pain and does not usually affect vision.
The eyes are most sensitive to UV radiation from 210 nm to 320 nm (UV-C and UV-B). Maximum absorption by the cornea occurs around 280 nm. Absorption of UV-A in the lens may be a factor in producing cataract (a clouding of the lens in the eye).
The danger to the eye is enhanced by the fact that light can enter from all angles around the eye and not only in the direction you are looking. The lens can also be damaged, but since the cornea acts as a filter, the chances are reduced. This should not lessen the concern over lens damage however, because cataracts are the direct result of lens damage.
Controlling UV Exposure
Steps to Reduce Exposure to UVR
Users must be trained regarding the hazards of UV radiation, signs and symptoms of an exposure, and proper use of UV producing equipment. Training needs to be documented inthe lab safety notebook.
Before using devices that produce UVR, read the equipment's user manual. The manual will tell you important information such as:
- Whether there are any UV protective shields or interlocks
- How interlocks function, where available
- When you are at risk for exposure
Inspect personal protective equipment prior to using a UVR device. Required protective equipment is based on the device in use, but may include:
- UV protective safety glasses
- UV protective face shield
- Skin protection, which may include a lab coat and disposable gloves
Before working with UVR devices, don the appropriate PPE
- Ensure workers around you are aware of your use of a device with UVR so they don't receive an indirect overexposure
- Limit exposure to UVR
- Place re-usable personal protective equipment such as a face shield in a set location so it is accessible to all researchers
UV Protection for Skin
- Most lab coats are effective at preventing UV exposure to skin
- Latex or nitrile gloves are effective at protecting hands
- Be aware of gaps in protection at the wrist or neckline
UV Protective Safety Glasses and Face Shield
How do you know your safety glasses and face shield provide UV protection?
All safety glasses and re-usable face shields should be marked Z87 which indicates basic requirements of the standard or Z87+ which indicates high-impact requirements of the standard. Not all safety glasses and face shields are designed to protect against UVR. New safety glasses or face shields should be marked with a "U" and Scale Number (Scale ranges from 2 to 6 – the higher the number the highest protection from far and near UV). Older safety glasses or face shields may be marked with UV or no marking at all. If there is no marking, do not assume it provides protection against UVR. Those with UVR protection protect against 99.9% of UVR. According to manufacturers, this coating does not wear off over time.
Regular eyeglasses, contact lenses, or typical safety glasses do not offer appropriate protection.
Do not forget to protect the rest of your face, too. Severe skin burns can happen in a very short time, especially under your chin (where most people forget to cover). Full-face shields are really the only appropriate protection when working with UV light boxes for more than a few seconds.