Ultraviolet (UV) radiation occupies the portion of electromagnetic spectrum from 100 to 400 nanometers (nm). The UV spectrum consists of three regions, as designated by the Commission Internationale de l’Eclairage:
- UV-A (315–400 nm)
- UV-B (280–315 nm)
- UV-C (100–280 nm)
For most people, the main source of UV exposure is the sun. Exposure from the sun is typically limited to the UV-A region, since the earth’s atmosphere protects us from the more harmful UV‑C and UV-B regions. Limiting our exposure time and using sunscreen lotions are two easy, effective methods for controlling overexposure to UV radiation. Only artificial light sources emit radiant energy within the UV-C band. Wavelengths below 180 nm (vacuum UV) are of little practical biological significance since they are readily absorbed by the air.
Because of its ability to cause chemical reactions and excite fluorescence in materials, UV light has a large number of useful applications in modern society. Listed below are some of the uses of specific wavelength bands in the UV spectrum:
- 13.5 nm: Extreme ultraviolet lithography
- 30–200 nm: Photoionization, ultraviolet photoelectron spectroscopy
- 230–365 nm: UV-ID, label tracking, barcode scanners
- 200–400 nm: Forensic analysis, drug detection
- 230–400 nm: Optical sensors, various instrumentation
- 240–280 nm: Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm)
- 270–360 nm: Protein analysis, DNA sequencing, drug discovery
- 280–400 nm: Medical imaging of cells
- 300–320 nm: Light therapy in medicine
- 300–365 nm: Curing of polymers and printer inks
- 300–400 nm: Solid-state lighting
- 350–370 nm: Bug zappers (flies are most attracted to light at 365 nm)
Adverse health effects associated with exposure to UVR are rated in severity according to wavelength and duration of exposure. The most significant adverse health effects have been reported at wavelengths below 315 nm, known collectively as actinic ultraviolet.
The effect of UV exposure is not felt immediately; the user may not realize the danger until after the damage is done. Symptoms typically occur 4 to 24 hours after exposure. It is important to note that UV radiation is harmful to both skin and eyes.
The effects on skin are of two types: acute and chronic. Acute effects appear within a few hours of exposure, while chronic effects are long-lasting and cumulative and may not appear for years. An acute effect of UVR is redness of the skin (called erythema), similar to sunburn. Chronic effects include accelerated skin aging and skin cancer.
The eyes are very sensitive to UV radiation. Prolonged direct exposure to UV-B and UV-C light can cause serious effects such as conjunctivitis and photokeratitis. Conjunctivitis is an inflammation of the membranes lining the insides of the eyelids and covering the cornea. Photokeratitis manifests as an aversion to bright light. The severity of these conditions depends on the duration, intensity, and wavelength. Symptoms may appear 6 to 12 hours after exposure and may subside after 24 to 36 hours with no permanent damage.
Unlike the skin, the eyes do not develop a tolerance to repeated exposure to UV. The absorption of UV-A radiation in the lens of the eye may produce progressive yellowing with time and may contribute to the formation of cataracts, causing partial or complete loss of transparency.
|Band||Wavelength (nm)||Primary Visual Hazard||Other Visual Hazards||Other Hazards|
|UV-A||315–400||Cataract of lens||Skin cancer, retinal burn|
|UV-B||280–315||Corneal injuries||Cataract of lens, photokeratitis||Erythema (sunburn), skin cancer|
|UV-C||220–280||Corneal injuries||Photokeratitis||Erythema, skin cancer|
|Far UV||190–220||Absorbed completely in the atmosphere|
|Vacuum UV||40–190||Absorbed completely in the atmosphere|
Factors That May Affect Sensitivity to UV Radiation
The extent of damage from exposure to UV radiation depends on several factors. It is commonly known that paler-skinned people are more photosensitive than darker-skinned people; yet high exposures to artificial sources of UV can cause damage to any skin type. Certain drugs, chemicals, and dietary and herbal agents can affect an individual’s sensitivity to UV. Skin conditions or eye infections can also result in increased photosensitivity, even in people who are not normally photosensitive. It is important to note that guidelines for the use of filters in protective equipment may not address these sensitivities, so extra precautions may be necessary.
Common Sources of UV Radiation
UV radiation is used in a wide variety of medical and industrial processes for killing bacteria or producing fluorescence; these include photocuring of inks and plastics (UV-A and UV-B), photoresist processes (all UV), solar simulation (all UV), cosmetic tanning (UV-A and UV-B), and dentistry (UV-A). UVR is also used in UV light boxes (transilluminators), germicidal lamps, and UV crosslinkers. Other artificial UV sources are solid-state light sources, such as light-emitting diodes (LEDs) and lasers. In addition, UV radiation is a by-product of processes such as welding and plasma cutting.
Germicidal lamps are used in a variety of applications where disinfection is the primary concern, such as air and water purification, food and beverage protection, and sterilization of sensitive tools such as medical instruments. They emit radiation almost exclusively in the UV-C range. The wavelength with the greatest effectiveness is 253.7 nm, which defines the germicidal category. Germicidal light destroys the ability of bacteria, viruses, and other pathogens to multiply by deactivating their reproductive capabilities.
Lamps that generate energy of wavelengths shorter than 250 nm (particularly 185 nm) are very effective in producing ozone, which is required for certain applications to oxidize organic compounds. Germicidal lamps are commonly used in Laminar Air Flow hoods or biological safety cabinets. In some cases, germicidal lamps may be used in special overhead light fixtures to sterilize entire rooms; these should be treated with extreme caution.
UV transilluminators or UV light boxes are used in biotechnology for visualization of nucleic acids (DNA or RNA) after gel electrophoresis and ethidium bromide staining. 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 254 nm, 312 nm, and 365 nm. Most of these instruments are stationary, but a few hand-held types carry the same hazards as the stationary models.
NEVER use a transilluminator without its protective shield in place.
An apparatus called a UV crosslinker is used to “cross-link” to covalently attach nucleic acid to a surface or membrane using techniques such as 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.
A solar simulator (also referred to as an artificial sun) is a device that provides illumination approximating natural sunlight. The purpose of the solar simulator is to provide controllable laboratory conditions for the testing of solar cells, sun screen, plastics, and other materials and devices. The three main types of solar simulators are continuous, flashed, and pulsed, depending on the use. Lamp types used as light sources for solar simulators include xenon arc, metal halide arc, and LED lamps.
UV Curing Systems
UV curing is a speed curing process in which high-intensity UV light is used to create a photochemical reaction that instantly cures inks, adhesives, and coatings. The curing systems are widely used in optical, fiber-optic, electronic, laser, microelectronic, and semiconductor applications. The curing can be a small-area spot curing, flood curing, hand-held, or conveyor curing. The UV systems use a variety of UV/visible arc lamps as UV light sources: mercury vapor lamps (with additives such as iron and gallium), fluorescent lamps, and LEDs.
Plasma etchers are designed for deposition and etch processes on silicon wafers and other substrates. Designed as modular systems, they use radio frequency (RF) and microwave power to create plasma inside a process chamber. Several hazards, including hazardous process gases and chemicals, are associated with plasma etchers. UV radiation is often a secondary hazard from plasma. UV light can also escape from other parts of the system (e.g., inductively coupled plasma sources and downstream plasma discharge tubes). Careful filtering and shielding is required to avoid UV exposure.
The chamber viewports are considered to be a particular risk area. Some viewports protect against UV light emission and RF energy emission, and incorporate an implosion guard. They are fitted with clear plastic UV filters, as well as a metal grid to provide shielding from RF radiation. Viewports are typically made of either glass or quartz. Ensure that these viewports are correctly assembled and are undamaged. If a filter is not fitted properly, or if there is uncertainty about whether it is fitted properly, contact the manufacturer for advice before operating the equipment. The UV filter inside the viewport assembly is critical for the operator’s safety.
System safety interlocks are in place to protect different functions like enabling RF power and enabling process gases. Unfortunately, UV filters are not a part of the interlock systems.
Never operate the equipment if the RF and UV filters are not in place or if any panels have been removed.
Portable UV Sources
Xenon flash lamp
A xenon arc lamp is a specialized type of gas discharge lamp that produces light by passing electricity through ionized xenon gas at high pressure. It produces a bright white light that closely mimics natural sunlight. Xenon arc lamps are used in movie projectors in theaters, in searchlights, and in industry and research to simulate sunlight. Other applications include air pollution analysis, biochemical analysis, blood or urine analysis, color sensing, factory automation, gas analysis, precision photometry, semiconductor inspection, shape inspection, and spectrophotometry.
Tungsten halogen lamp
Tungsten halogen lamps are ideal light sources for spectrophotometers as they provide broadband spectral radiation ranging from UV, through the visible, and into the infrared out to 5 microns. They are excellent for bright-field examination, photomicrography, and digital imaging of stained cells and tissue sections, as well as numerous reflected light applications for industrial manufacturing and development.
A mercury vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. Clear mercury lamps produce white light with a bluish-green tint (the result of mercury’s combination of spectral lines).
In low-pressure mercury vapor lamps, only the lines at 184 nm and 253 nm are present. In medium-pressure mercury vapor lamps, the lines from 200 to 600 nm are present. The lamps can be constructed to emit primarily in the UV-A (around 400 nm) or UV-C (around 250 nm). High-pressure mercury vapor lamps are commonly used for general lighting purposes. They emit primarily blue and green light.
Light-emitting diode lamp (LED)
An LED lamp produces light at a single wavelength, without the need for a monochromator. Because LED life is almost infinite, and the light spectrum is stable, with little variation in bandwidth, LEDs are an attractive low-cost solution for simple applications.
Deuterium arc lamp
A deuterium arc lamp (or simply deuterium lamp) is a low-pressure gas-discharge light source often used in spectroscopy when a continuous spectrum in the UV region is needed. Deuterium arc lamps emit in the UV region 190–370 nm. Because the lamp operates at high temperatures, normal glass housings cannot be used for a casing. Instead, a fused quartz, UV glass, or magnesium fluoride envelope is used, depending on the specific function of the lamp.
Whenever possible, UV lamps should be used under totally enclosed, interlocked conditions. Interlocks must not be intentionally defeated unless the hazards are otherwise well controlled.
Other Hazards Associated with UV Light
Do not touch the lamp with bare skin. Skin oils on a hot lamp permanently etch the quartz (devitrification), causing local overheating. Strain buildup leads to premature, catastrophic failure. Wiping the lamp with alcohol before installation is a useful precaution.
High-pressure lamps have the potential to explode; therefore, care must be taken when removing or replacing such lamps to protect eyes and skin from flying shards. Wait for the lamp to cool down completely before attempting removal.
Ozone is produced by the absorption of short-wavelength UV by oxygen. Ozone is a powerful oxidizing agent and can damage cells, especially in the lungs. Ensure that adequate ventilation is available when using intense sources of short-wavelength UV-B and UV-C.
Phosgene is formed when a chlorinated hydrocarbon solvent or PVC is exposed to UV radiation or intense heat. Even very small amounts of phosgene coming into contact with any moisture in the lungs will produce hydrogen chloride and damage lung tissue.
Be aware of the hazards associated with a particular artificial source of UV; if any uncertainty or concern exists regarding safety, contact the point of contact in the Non-ionizing Radiation (NIR) Program for advice.
UV Exposure Limits
There are no federal or State of California safety standards that specify permissible occupational exposure levels to UV radiation. For the most part, UV exposures are covered under the Occupational Safety and Health Administration (OSHA) “General Duty Clause,” which requires employers to protect workers from recognizable hazards. However, federal law (10 CFR 851) mandates the application of UV exposure levels (Threshold Limit Values, or TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH). A TLV is the limit of exposure to a chemical substance by a healthy worker repeatedly, day after day, without adverse health effects. Adverse health effects include erythema (redness similar to sunburn) or photoconjunctivitis. Berkeley Lab implements the 2016 ACGIH TLVs as required by 10 CFR 851.
The TLVs for exposure to UV radiation are provided in units of millijoules of energy per square centimeter of surface area (mJ/cm2). They are presented as a function of wavelength from 180 nm to 400 nm for wavelength-dependent exposure times that need to be calculated using a parameter termed the relative spectral irradiance. The TLV values indicate the following:
- The most hazardous UV radiation has wavelengths between 240 nm and 300 nm. In this wavelength range, the TLV is less than 10 mJ/cm2, with the minimum TLV (the most hazardous radiation) being 270 nm (TLV = 3 mJ/cm2)
- The least hazardous UV radiation has wavelengths exceeding about 315 nm (UV‑A radiation). Above that wavelength, the TLV is always over 1,000 mJ/cm2, and it steadily climbs above that wavelength, indicating that the radiation is less hazardous with increasing wavelength.
- Between 180 nm and 240 nm, the radiation becomes increasingly more hazardous to up to 10 mJ/cm2 at 240 nm.
Where information on cumulative exposure from the UV source is available or easily measurable, comparison with exposure limits can identify what control measures may be needed. However, radiometric measurements are difficult to carry out accurately, and exposure often cannot be measured, so a precautionary approach must be taken.
Limiting UV Exposure
Control measures must be in place to limit exposure to eyes and skin and to prevent cumulative exposure. The precautions needed depend on the risk assessment. Control measures designed to eliminate the risk of exposure to UV at its source, such as engineering and administrative controls and personal protective equipment (PPE), must be implemented wherever possible. A key element in achieving the goal of reduced UVR exposure is worker training and awareness.
Having equipment located in a separate room, alcove, or low-traffic area of a lab is ideal. To help prevent exposure to other employees, avoid placing equipment in the direct vicinity of desk areas or other equipment.
The use of light-tight cabinets and enclosures is the preferred means of preventing exposure. Where it is not practicable to fully enclose the UV source, use screens, shields, and barriers. Covers or partial enclosures must not be removed when the equipment is in use. If they are discolored, degraded, or damaged in any way, they should be replaced.
Some equipment comes with interlock devices. Interlocks must not be tampered with. They should be replaced or repaired when defective.
Typical administrative controls include limiting access to UV sources, ensuring that personnel are aware of the potential hazards, and providing personnel with training and safe working instructions.
Personnel should carefully study the manufacturer’s manuals for the UV-generating equipment and be familiar with its use. The manufacturer’s manuals provide specific safety-related information (type of eye/skin protection needed, ventilation requirements, etc.) that must be completely understood before using the equipment. It is important never to deviate from the instructions for safe operation. If any uncertainty or concern exists regarding the safe use of UV-generating equipment, contact the manufacturer for clarification.
At a minimum, lab personnel should be familiar with the following when working with or around UV light:
- Proper use of the UV light–producing equipment
- Warning signs and labels
- Proper use of protective equipment provided by the manufacturer (e.g., UV shields/enclosures), as well as PPE
- Symptoms of UV exposure
- Never view the UV lamp directly. Although the inverse square law applies to non-laser-beam UV radiation, it is not advisable to look directly at any UV source (e.g., an arc lamp) – at any distance.
- Keep exposure time to a minimum, and where the source is not enclosed or shielded, keep as far away from it as practicable.
- Restrict access to those personnel who are directly concerned with the operation of the UV source.
Hazard warning signs
Warning signs are necessary unless the UV radiation is completely enclosed and there is no risk of exposure during use and maintenance. Warning signs should be used where applicable to indicate the presence of potential UVR hazards, to restrict access, and to select appropriate PPE.
Shown below are some variations of the UV hazard warning sign.
Personal Protective Equipment (PPE)
Depending on the risk assessment, appropriate PPE may include eyewear, face shields, gloves, and lab coats.
Use eyewear that is appropriate for the work. Special safety glasses are available for the different UV ranges. For best UV protection, the eyewear should be compliant with ANSI Z87.1. ANSI Z87.1 requires markings on eye protection that relate directly to the device’s ability to defend against specific hazards. Eye protection that is Z87.1-compliant is marked with “Z87.” Additional markings fall into three categories: impact vs. non-impact, splash and dust protection, and optical radiation protection.
- Impact vs. non-impact. ANSI Z87.1 has two classifications for eye protection: impact-rated and non-impact-rated. Impact-rated eye protection must pass certain high-mass and high-velocity tests and should provide eye protection from the side. Impact-rated eye protection will have a plus symbol (+); for example, ANSI-compliant impact-rated flat lenses are marked “Z87+.”
- Chemical splash and dust protection. Eyewear that meets the ANSI Z87.1 requirement for droplet (splash) or dust protection will be marked with a code that begins with the letter “D.” Markings for different kinds of protection are as follows:
- For droplets and splashes – “D3”
- For dust – “D4”
- For fine dust – “D5”
- Optical radiation protection. A lens’s ability to protect against radiation is indicated by a letter designation, which is typically followed by a rating number. The markings are as follows:
- Welding filter: “W” followed by a shade number on a scale from 1.3 to 14
- Ultraviolet (UV) filter: “U” followed by a number on a scale from 2 to 6
- Infrared (heat) filter: “R” followed by a number on a scale from 1.3 to 10
- Visible light (glare) filter: “L” followed by a number on a scale from 1.3 to 10
- Clear lens: No additional marking
- Variable tint: “V”
- Special purpose: “S”
- When appropriate, two additional markings will appear on eye protection:
- Eye protection designed for a smaller head size will be marked with the letter “H.”
- Prescription lenses will have the manufacturer’s logo.
The marking XXZ87+U6D3D4, for example, indicates that the goggles provide superior UV filtration and protection against splash and dust hazards. The “XX” is reserved for the manufacturer’s name.
UV-absorbing full face shields should be worn in addition to safety glasses or goggles (goggles may not provide sufficient face protection). Severe skin burns can happen in a very short time, especially under the chin (which is often left exposed). Full face shields are the only appropriate protection when working with UV light boxes for more than a few seconds.
At a minimum, nitrile, latex, or tightly woven fabric gloves are recommended to protect against the significant amounts of UV-A and UV-B that may pass through to the skin; these types of gloves have a low transmission of UV compared to vinyl gloves. Gloves should protect personnel from UV light, as well as from the hazard of the activity being performed.
Personnel should wear lab coats that fasten securely at the wrists and up the neck so that no skin is exposed. Note that burns to wrists and the neck are not uncommon.
Tyvek® protective wear, such as arm shields, coveralls and lab coats, is NOT appropriate PPE because it may allow significant leakage of UV through it.
PPE must be either readily available and cleaned between users or personally allocated to each user. Eye and face protection must be inspected either regularly or before each use for damage or defects such as cracks, crazing, or bleaching, and replaced when necessary. Note that PPE may need to serve multiple purposes, such as protecting against both chemical splashes and UV.
Disposal of UV-Generating Devices
Many UV-generating devices have UV light bulbs that can be replaced. DO NOT dispose of UV bulbs in the regular trash. Disposal of these bulbs must be handled through Environment, Health & Safety (EHS) because the bulbs may contain mercury and are considered hazardous. They are subject to certain regulatory requirements for disposal. Contact your waste generator for assistance.
The signs and symptoms of an accidental exposure would be erythema of the skin (similar to sunburn) and possible inflammation of the eye caused by lesions on the cornea.
If you believe that you have been exposed to UV radiation, take the following steps:
- Immediately discontinue the use of the UV-producing equipment and turn it off.
- Immediately seek medical care for skin and eye exposures.
- Notify your supervisor as soon as you can, no matter how minor the injury may seem.
- Report all unsafe working conditions to your supervisor or the NIR subject matter expert in the EHS Division.