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A Laser is a light source that can be dangerous to people exposed to it. Even low power lasers can be hazardous to a person's eyesight. The Coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the Retina , resulting in localised burning and permanent damage in seconds. Certain wavelengths of laser light can cause Cataract s or even boiling of the Vitreous Humour , the fluid in the eyeball. Infrared and ultraviolet lasers are particularly dangerous, since the body's " Blink Reflex ", which can protect an eye from excessively bright light, works only if the light is visible. CLASSIFICATION In the United States lasers are classified by wavelength and maximum output power into the following safety classes, (the international classification is slightly different): Old system ;class I: Inherently safe; no possibility of eye damage. This can be either because of a low output power (in which cases eye damage is impossible even after hours of exposure), or due to an enclosure that cannot be opened in normal operation without the laser being switched off automatically, such as in CD players. ;class II: The blinking reflex of the human eye ( Aversion Response ) will prevent eye damage, unless the person deliberately stares into the beam. Output powers up to 1 mW. This class is for Visible Light lasers only. ;class IIIa: Lasers in this class are mostly dangerous in combination with optical instruments which change the beam diameter. Output powers 1–5 mW. This class is for Visible Light lasers only. Most Laser Pointer s are in this category. ;class IIIb: Can cause damage if the beam enters the eye directly or if the beam is directly reflected into the eye. This generally applies to lasers powers from 5–500 mW. Diffuse reflection is not considered hazardous and the laser doesn't present a fire hazard. ;class IV: Highly dangerous; even indirect scattering of light from the beam can lead to eye or skin damage. This generally applies to laser powers of more than 500 mW, or lasers that produce intense pulses of light. Although the intensity of the beam may be only a few times that of bright sunlight, when it enters the eye the beam can be focused on a very small spot near its Diffraction Limit . The laser powers mentioned above are typical values; the classification is also dependent on the wavelength and on whether the laser is pulsed or continuous. Also, even a high power laser may be assigned to a low safety class if it is enclosed so that no laser radiation can leave the case and injure a person. Revised system ;class I :A class 1 laser is safe for use under all reasonably-anticipated conditions of use; in other words, it is not expected that the maximum permissible exposure (MPE) can be exceeded. This class may include lasers of a higher class whose beams are confined within a suitable enclosure so that access to laser radiation is physically prevented. ;class IM :Class 1M lasers produce large-diameter beams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow down the beam. If the beam is refocused, the hazard of Class 1M lasers may be increased and the product class may be changed. ;class II :A class 2 laser emits in the visible region. It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, although prolonged viewing may be dangerous. ;class IIM :A class IIM laser emits in the visible region in the form of a large diameter or divergent beam. It is presumed that the human blink reflex will be sufficient to prevent damaging exposure, but if the beam is focused down, damaging levels of radiation may be reached and may lead to a reclassification of the laser. ;class IIIR :A class 3R laser is a continuous wave laser which may produce up to five times the emission limit for Class 1 or class 2 lasers. Although the MPE can be exceeded, the risk of injury is low. The laser can produce no more than 5 mW in the visible region. ;class IIIB :A class 3B laser produces light of an intensity such that the MPE for eye exposure may be exceeded and direct viewing of the beam is potentially serious. Diffuse radiation (i.e., that which is scattered from a diffusing surface) should not be hazardous. CW emission from such lasers at wavelengths above 315 nm must not exceed 0.5 watts. ;class IV :Class 4 lasers are of high power (typically more than 500 mW if cw, or 10 J/cm2 if pulsed). These are hazardous to view at all times, may cause devastating and permanent eye damage, may have sufficient energy to ignite materials, and may cause significant skin damage. Exposure of the eye or skin to both the direct laser beam and to scattered beams, even those produced by reflection from diffusing surfaces, must be avoided at all times. In addition, they may pose a fire risk and may generate hazardous fumes. (From The Physical and Theoretical Chemistry Laboratory Oxford University) {Link without Title} PROTECTIVE EYEWEAR Inside an environment with exposed laser beams, it is recommended that everyone wears suitable eye protection. In the U.S. , guidance for the use of protective eyewear, and other elements of safe laser use, is given in the ANSI Z136 series of standards. They are: :ANSI Z136.1 - Safe Use of Lasers :ANSI Z136.2 - Safe Use of Lasers in Optical Fiber Communication Systems Utilizing Laser Diode and LED Sources :ANSI Z136.3 - Safe Use of Lasers in Health Care Facilities :ANSI Z136.5 - Safe Use of Lasers in Educational Institutions :ANSI Z136.6 - Safe Use of Lasers Outdoors In the European Community , eye protection requirements are specified in the European norm EN 207 . In addition to the EN 207 norm, there is the European norm EN 208 norm that specifies requirements for goggles for use during alignment. These transmit a small fraction of the laser light in order to allow the operator to see where the beam is. The latter does not provide sufficient protection against a direct hit of the laser beam. Finally, the European norm ''EN 60825'' specifies the required optical densities in extreme situations. GUIDELINES The use of eye protection when operating lasers of classes IIIb/IIIB and IV is strongly recommended and required in the workplace by the U.S. Occupational Safety And Hazard Administration (OSHA) . It is common in scientific research, however, for operators to remove their eye protection during certain procedures, or even to avoid wearing it altogether. The problem is that the use of safety glasses over a long time is often uncomfortable, and in many types of optical experiments it is also somewhat inconvenient. For example in Spectroscopy , the experimental arrangement is constantly being modified and fine-tuned, during which it often is necessary to see where the beam is going. This is often most simply achieved with the naked eye, rather than (for example) with a camera. In this situation, many scientists assign a higher priority to convenience and comfort than to safety, and routinely breach the laser safety regulations. Sometimes it is unavoidable when working with, for example, an RGB laser, which would technically require completely black goggles. Although not everybody agrees on these practices, most scientists involved with lasers agree about the following guidelines.
Dangerous styles of working are encouraged (but not justified) by various factors, including:
ELECTRICAL SAFETY For the main article on general electrical safety, see High-voltage Hazards . A discussion of laser safety would not be complete without general electrical safety. Lasers are often high voltage, typically 400V upward for a small 5mJ pulsed laser, and exceeding many kilovolts for higher powered lasers. This coupled with high pressure water for cooling the lasers and often many other associated electrical pieces of equipment can in combination often provide more of a hazard than the laser beam itself. It is absolutely essential that every piece of electric equipment is at least 10 inches off of the floor to reduce electric risk in the case of flooding. The optical table, laser and any other equipment should be fully grounded. EXTERNAL LINKS
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