Maximum permissible exposure

Safety Standards. Protection from laser beams involves not allowing laser radiation at a level higher than a maximum permissible exposure level to strike the human body. Maximum permissible exposure levels for both eyes and skin have been defined (55—57). One of the most common safety measures is the use of protective eyewear. Manufacturers of laser safety eyewear commonly specify the attenuation at various laser wavelengths. Under some conditions safety eyewear has been known to shatter or to be burned through (58), and it is not adequate to protect a wearer staring directly into the beam. 

Eor evaluation of a particular laser installation, the standard should be consulted to determine the classification of the laser and appropriate safety measures. The maximum permissible exposure for the particular laser also should be determined in order to select the appropriate protective eyewear. 

The handling of arsenic in the workplace should be in compliance with the Occupational Safety and Health Administration (OSHA) regulations the maximum permissible exposure limit for arsenic in the workplace is 10 p-g/m of air as deterrnined as an average over an 8-h period (33). 

NCRP (1954). National Council on Radiation Protection and Measurements. Permissible Dose from External Sources of Ionizing Radiation (1954) including Maximum Permissible Exposure to Man, Addendum to National Bureau of Standards Handbook 59 (1958) (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 

The need for improved sampling and analytical techniques for monitoring employee exposure extends to substances other than the trace metals. The "no detectable limit philosophy for occupational exposure to carcinogens dates back to the 1974 situation with vinyl chloride in which NIOSH recommended that airborne concentrations be reduced "to levels not detectable by the recommended method (1 ppm) (16). Very low maximum permissible exposure levels are likely to be recommended in the future for substances which are determined to be potential human carcinogens. 

Table 10-3. Design Values of Flux and Intensities for Maximum Permissible Exposure (MPE)...

To permit maximum permissible exposure (MPE) conditions or less (see Table 10-3), the source strength must be divided by an area term... 

A class 1 laser is safe under all conditions of normal use. Never exceed the maximum permissible exposure (MPE) limit. This class includes high-power lasers within an enclosure that prevents exposure to the radiation and that cannot be opened without shutting down the laser. For example, a continuous laser at 600 nm can emit up to 0.39 mW, but for shorter wavelengths, the maximum emission is lower because of the potential of those wavelengths to generate photochemical damage. The maximum emission is also related to the pulse duration in the case of pulsed lasers and the degree of spatial coherence. 

Maximum permissible exposure—The level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin. 

The highest dose (exposure) that can be received safely by the eye from a laser beam is called the maximum permissible exposure (MPE) measured in watts/cm or joules/cm. At the MPE a laser has virtually no probability of causing damage if an eye exposure occurs. MPE is dependent on several factors laser energy, laser wavelength, incident time upon the target, and the light-source spatial distribution (also called spatial coherence). 

Qass Maximum permissible exposure (MPE) Maximum power Safety precautions... 

The U.S. Army publication Technical Bulletin Medical 524 (Note 16) identifies maximum permissible exposures (MPE). The MPE is the level of laser radiation exposure allowed without hazardous effects or adverse biological changes to the eyes or skin. Because exposures at the MPE may be uncomfortable to view or sensitive to the skin, actual exposure levels should be as far below the MPE as possible. 

Download a copy of U.S. Army Technical Manual Medical 524, especially the appendix with Maximum Permissible Exposures (MPEs). Using this standard, answer the following ... 

When the entire beam path from a Class IIIB or Class IV laser is not sufficiently enclosed or baffled to ensure that radiation exposures do not exceed the maximum permissible exposure, a laser-controlled area is required. During periods of service, a controlled area may be established on a temporary basis. Two controls are required for both Class IIIB and Class IV installations (1) posting with appropriate laser warning signs, and (2) operated by qualified and authorized personnel. 

All windows, doorways, open portals, etc. of an enclosed facility should be covered or restricted to reduce any escaping laser beams below appropriate ocular Maximum Permissible Exposure (MPE) level, and require storage or disabling of lasers when not in use. 

The various standards then apply a safety factor of some magnitude to arrive at their maximum permissible exposure (MPE) guidelines. The three most relevant standards are ANSI C95.1-1982, the successor standard ANSI C95.1-1992, and NCRP-86 (adopted in 1986). Each has a safety factor of 10 times, with ANSI-82, ANSI-92 (controlled environments), and NCRP-86 (occupational) reflecting a maximum SAR of 0.4 W/kg. In certain cases, a second tier is suggested, to reflect a possible (but not demonstrated) increase in susceptibility on the part of the infirm, the aged, or the very young. The second tier safety factor in ANSI-92 and NCRP-86 is 50 times, that is, five times tighter than the controlled/occupational limit. 

Maximum permissible exposure (MPE) The limit adopted by a standards-setting body for exposures of unlimited duration. Generally, some allowance is made in the standard for time and/or space averaging of higher exposure conditions. 

George, 1941-. IV. Series. [DNLM 1. Metals - toxicity. 2. Maximum Permissible Exposure Level. 

Confocal detection schemes enable Raman signal to be obtained from well-defined volumes within a thick sample [24-26]. Jongsma et al, [27] developed a confocal Raman spectroscopy system for noncontact scanning of ocular tissues up to 13 mm deep into the eye (Fig. 8). It was used in various in vitro and in vivo studies that addressed the (monitoring of changes in) hydration of the cornea [28] and the diffusion of topically applied pharmaceuticals through the cornea [29]. Care was taken to stay below the maximum permissible exposure of the retina as defined by the American National Standards Institute [30]. 

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