Many devices (or sources) produce either broadband or discrete wavelength radiation between 100 nm and 1 mm. Under certain conditions, these sources may present a health hazard. Factors affecting the potential hazard include: the specific wavelength(s) produced, the irradiance value, the source dimensions, and whether the radiation can access the eye or skin. Sources include (but are not limited to) the following:
- Lamps (filament, discharge, fluorescent, arc, solid state, etc.)
- Plasma sources (welding devices, surface deposition, etc.)
- Heat sources (furnaces, molten glass, open flames, etc.)
Whenever practical, sources of non-coherent light not intended for illumination purposes should be shielded to prevent exposure to the eye or skin. For sources intended to produce exposure (lamps), any unneeded wavelengths (example: ultraviolet emitted from mercury vapor lamps) should be removed with appropriate filtration.
Ultraviolet (UV) radiation is defined as having a wavelength between 10 nm and 400 nm. Specific wavelength “bands” are defined by the CIE (Commission International de l’Eclairage or International Commission on Illumination) as follows:
Physical Definition
- Extreme UV (10 nm to 100 nm)
- Vacuum UV (10 nm to 200 nm)
- Far UV (200 nm to 300 nm)
- Near UV (300 nm to 400 nm)
Photobiologic Definition
- UV-C (100 nm to 280 nm)
- UV-B (280 nm to 315 nm)
- UV-A (315 nm to 400 nm)
Ultraviolet Skin Hazards
Ultraviolet (UV) radiation is a known carcinogen for human skin. In addition to cancer induction, erythema (sunburn), and skin aging are also known products of ultraviolet skin exposure. Because the biological effects are dependent on the time of exposure, the specific UV wavelength, and the susceptibility of the individual exposed, it is considered prudent to prevent any unnecessary skin exposure to UV sources. Elimination of unnecessary skin exposure is reinforced by the fact that most individuals will receive substantial UV exposure from the sun during normal outdoor activities over a human lifetime.
UV radiation causes biological effects primarily through photochemical interactions. The UV wavelengths that produce the greatest biological effects fall in the UV-B, but other wavelengths can also be hazardous.
Skin protection is not difficult in theory, as most clothing tends to absorb some of the UV wavelengths. However, in practice, it is often difficult to properly motivate individuals to use appropriate skin protection unless they know they are receiving an erythema (sunburn) dose.
Protection of the skin from UV radiation hazards is best achieved though the use of clothing, gloves, and face shields. The use of UV skin blocks (creams or lotions) is considered inadequate for protection against the high irradiance of man-made UV radiation sources.
Ultraviolet Eye Hazards
Various components of the human eye are susceptible to damage from extended exposure to direct/reflected UV exposure from photochemical effects. The UV wavelength is the determining factor as to which part(s) of the eye may absorb the radiation and suffer biological effects.
ABSORPTION OF UV WAVELENGTHS IN THE HUMAN EYE
|
Wavelength
|
Cornea
|
Aqueous
|
Lens
|
Vitreous
|
| 100 nm - 280 nm | 100% | 0% | 0% | 0% |
| 300 nm | 92% | 6% | 2% | 0% |
| 320 nm | 45% | 16% | 36% | 1% |
| 340 nm | 37% | 14% | 48% | 1% |
| 360 nm | 34% | 12% | 52% | 2% |
The cornea is like the skin in that it can be “sunburned” by exposure to too much UV radiation. This is called keratoconjunctivitis (snow blindness or welders flash), a condition where the corneal (epithelial) cells are damaged or destroyed. This condition usually does not present until 6 to 12 hours following the UV exposure. Although very painful (often described as having sand in the eyes) this condition is usually temporary (a few days) because the corneal cells will grow back. In very severe cases, the cornea may become clouded and corneal transplants may be needed to restore vision. Exposure to the UV-C and UV-B present the greatest risk to the cornea.
The lens of the eye is unique in that it is formed early in human development and is not regenerated should it become damaged. For normal vision, it is essential that the lens remains clear and transparent. Unfortunately, UV-A exposure is suspected as a cause of cataracts (clouding of the lens).
To protect the human eye from exposure to UV wavelengths, all that is usually needed is a pair of polycarbonate safety glasses or a polycarbonate face shield. This protective eyewear should be worn whenever there is a potential for ongoing UV radiation exposure. Contact the Office of Environment, Health & Safety (EH&S) for information and advice on appropriate UV protective eyewear.
Visible Light Hazards
All visible light (400 to 780 nm) entering the human eye is focused upon the sensitive cells of the retina where human vision occurs. The retina is the part of the eye normally considered at risk from visible light hazards.
Any very bright visible light source will cause a human aversion response (we either blink or turn our head away). Although we may see a retinal afterimage (which can last for several minutes), the aversion response time (about 0.25 seconds) will normally protect our vision. This aversion response should be trusted and obeyed. NEVER STARE AT ANY BRIGHT LIGHT SOURCE FOR AN EXTENDED PERIOD. Overriding the aversion response by forcing yourself to look at a bright light source may result in permanent injury to the retina. This type of injury can occur during a single prolonged exposure. Welders and other persons working with plasma sources are especially at risk for this type of injury.
NOTE: The aversion response cannot be relied upon to protect the eye from Class 3b or 4 laser exposure (see the Laser Safety Manual for more information).
Visible light sources that are not bright enough to cause retinal burns are not necessarily safe to view for an extended period. In fact, any sufficiently bright visible light source viewed for an extended period will eventually cause degradation of both night and color vision. Appropriate protective filters are needed for any light source that causes viewing discomfort when viewed for an extended period of time.
For these reasons, prolonged viewing of bright light sources (plasma arcs, flash lamps, etc.) should be limited by the use of appropriate filters. Traditionally, welding goggles or shields of the appropriate “shade number” will provide adequate protection for limited viewing of such sources. Please contact EH&S for advice on appropriate eye protection.
The blue light wavelengths (400 to 500 nm) present a unique hazard to the retina by causing photochemical effects similar to those found in UV radiation exposure. Visible light sources strongly weighted towards the blue should be evaluated by EH&S to determine if special protective eyewear is needed.
Infrared Radiation
Infrared (or heat) radiation is defined as having a wavelength between 780 nm and 1 mm. Specific biological effectiveness “bands” have been defined by the CIE (Commission International de l’Eclairage or International Commission on Illumination) as follows:
- IR-A (near IR) (780 nm to 1400 nm)
- IR-B (mid IR) (1400 nm to 3000 nm)
- IR-C (far IR) (3000 nm to 1 mm)
Infrared Radiation Hazards
Infrared radiation in the IR-A that enters the human eye will reach (and can be focused upon) the sensitive cells of the retina. For high irradiance sources in the IR-A, the retina is the part of the eye that is at risk. For sources in the IR-B and IR-C, both the skin and the cornea may be at risk from “flash burns.” In addition, the heat deposited in the cornea may be conducted to the lens of the eye. This heating of the lens is believed to be the cause of so called “glass blowers” cataracts because the heat transfer may cause clouding of the lens.
- Retinal IR Hazards (780 to 1400 nm) - possible retinal lesions from acute high irradiance exposures to small dimension sources.
- Lens IR Hazards (1400 to 1900 nm) - possible cataract induction from chronic lower irradiance exposures.
- Corneal IR Hazards (1900 nm to 1 mm) - possible flashburns from acute high irradiance exposures.
- Skin IR Hazards (1400 nm to 1 mm) - possible flashburns from acute high irradiance exposures.
The potential hazard is a function of the following:
- The exposure time (chronic or acute)
- The irradiance value (a function of both the image size and the source power)
- The environment (conditions of exposure)
Evaluation of IR hazards can be difficult, but reduction of eye exposure is relatively easy through the use of appropriate eye protection. As with visible light sources, the viewing of high irradiance IR sources (plasma arcs, flash lamps, etc.) should be limited by the use of appropriate filters. Traditionally, welding goggles or shields of the appropriate “shade number” will provide adequate protection for limited viewing of such sources. Specialized glassblowers goggles may be needed to protect against chronic exposures. Please contact the EH&S for advice on appropriate eye protection.