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precluded, but their use and potential for direct expo- $ure should be considercd. Flame resictant materials should be encouraged. 7.6 Laser Operation in Outdoor Environments 7.6.1 Use of Lasers in Navigable Airspace, The Federal Aviation Administration (FAA) is responsible for regulating the use and efficient utilization of navigable airspace to ensurc the safety of aircraft and the protection of people and propefly on the ground. Laser experiments or programs that will involve the use of navigable airspace should be coordinated with the FAA (Washington, DC 20590, or any FAA regional office) in the planning stages to ensure pmper control of any attendant hazard to airbome personnel or equipment. 7.6.2 Laser Beam Attenuation. The effects of attenuation on a laser beam traveling through a homogeneous but lossy medium can be trested at visible wavelengths by using an exponential attenuation coefficient. (See B.4.) For propagation at longer wavelengths, individual lines must be separately determined, panicularly at wavelengths where the effects of waier vapor become important. 7.6.3 Scintillation, Scintillation arises from local variations in the refractive index of the medium through which a laser beam is propagated. It causes random pointing, spreading, blurring and energy redistribution of a beam. A "worst-case" analysis shall be used in evaluating the potential ocular hazard from such scintillation €ffects. NOTE: References useful for the special considerations covered in 7-l through 7.6 may be found in Appendix F. 8. Criteria for Exposure ofthe Eye and Skin Maximum prermissibte exposure (MPE) values are below known hazardous levels. Levels at the MPE values given may be uncomfonable to view or feel upon the skin. Thus, it is good practice to maintain exposure levels as far below the MPE values as is practicable. When a laser emits radiation at several widely different wayelengths, or where pulses are superimposed on a cw background, computation of the MPE is complex. Exposures from several wavelengths in the same time domain are additive on a proportional basis of specral effectiveness with due allowance for all correction factors. The simultaneous exposure to pulses and cw radiation is not strictly additive (there AMERICAN NATIONAL STANDARD 2I36.1-I986 may be synergism) and caution should be used in these situations until more data arc available. The limiting aperture shall be used for measurements and calculations with all MPE values. The limiting aperture is the maximum circular area over which irradiance and radiant exposure can be averaged. See Table 9 and Fig. 13 for proper application of this aPenurc. In the tabulations for MPE, values for irradiance can be obtained by dividing the radiant exposure by the time, t, in seconds, and values for radiant exposure can be obtained by multiplying the irradiance by r in seconds. NOTE: Exposure limits for pulse duralions less than I ns are Dot provided !1 lhc prescnt time becausc of a laqk of biological data. However, IEC Srandard 825 (1984) suggests limiting peak inadianc€s to the exposure limit applicable to nanosecond pulses. Appendix G provides reference material on this subject. 8.1 Intrabeam Viewing and Extend€d Source Ocular Exposures. For the purposes of this standard, sources such as laser arrays, diodes and diffuse reflecting surfaces are considered to be extended sources if their angular subtense (apparent visual angle) is equal to or greater than cr,;n as specifled in Fig.3. For all other laseni, including as those wilh collimated beams which produce a small (nearly diffractionlimited) retinal imag€ and also point sources, intrabeam viewing criteria applies. In this category the angular subtense is less than o-in. Sources such as laser arrays, multiple diodes, or multiple diffuse reflecting surfaces are treated as in[abeam viewing cases for any of the separate images whose angular subtense is less than (Iln6. Any sources whose centers are separated by an angle less than ohrin are treated as extended sources. See 9.2 for sources between 0.4 pm and L4 Um. Appropriate MPES are associated with each type of source, For intrabeam viewing criteria see 8.2t for extended-source viewing criteria see 8.3. NOTE: The angular subtense is not the beam divergence of the source. It is the apparent visual angle as calculated from the source size and distance from the eye. The limiting angular subtense is that apparent visual angle which divides intrabeam viewing from extended-source viewing. See B-3-2. 8.2 MPE for Inarabeam Viewing. The single pulse or single exposure MPE values for intrabeam viewing are given in Table 5. ln order to apply these MPE ZJ
AMERICAN NATIONAL STANDARD 2I36.I.I986 values, the information specified in 8.2.1 and 8.2.2 is required. (See 8.5 for special qualilications and use; see also Figs. 4,5,6 and 10.) 8.2,1 Wavelength. The wavelength must be specified to establish which specral region is applicable. The MPEs in Table 5 arc arranged in broad wavelength regions and by specific wavelength expressed in micrometers. Fot multiple wavelength laser emissions, the MPE must first be determined for each wavelength separately. In the ultraviolet rtgion, special considerations may apply for multiple exposures (see 8.2.2.1). 8.2,2 Exposure Duration. For a single-pulse laser, the exposure duration is equal to the pulse duration, r, defined at its half-power points. For a cw visible (0.4 to 0.7 pm) laser, the exposurc duration is the maximum time of anticipated direct exposure, fm"*, If purposeful staring into the beam is not intended or anticipat€d, then the aversion response time, 0,25 s, may be used. For non-visible wavelengths (less than 0.4 pm or greater than 0.7 Fm), the cw exposur€ duration is the maximum time of anticipated direct exposute, I.",. For the hazard evaluation of retinal exposures in the near-infrared (0.7 to 1.4 Fm), a maximum exposure duration of l0 s provides an adequate hazard criterion for either unintended or purposeful staring condi tions. In this case, eye movements will provide a nalural exposure limitation eliminating the need for exposure durations greater than l0s, except for unusual conditions. In special applications, such as medical instrumentation, even longer exposure durations may apply. For rep€titively pulsed lasers, the total exposure duration, I, of the train of pulses must be determined. This duration is determined in lhe same manner as is used for cw laser exposures. The method for determining the MPEs for repetitively pulsed laser exposures is given in 8.2.2.1 and 8.2.2.2. Forpulse widths less than I ns, see Note in Section 8. 8.2,2.lRepeated Exposures, Ultraviolet (0.315 to 0.4 pm) - Special Considerations. For repeated exposures, the exposure dose is additive over a 24-hour period, regardless of the repetition rate. The MPE for any 24-hour period should be reduced by a factor of 2.5 times relative to the single-pulse MPE if exposures on succeeding days are expected. 26 E.2.2,2 Repeated Exposures, Visible (0,4 to 0.7 pm) and Infrared (> 0.7 pm), Bolh scanned cw lasers and repetitively pulsed lasers can produce repetitively pulsed exposur€ conditions. The MPE per pulse for repetitively pulsed intrabeam viewing is a-rl4 times the MPE for a single pulse cxposure where r is the number of pulses found from the product of the prf and the exposure duration (f) as defined in 8.2.2. (See Figure 12 for a graphical repr€sentation of n-t14.) This MPE applies to all wavelengths greater than 0.7 pm (thermal injury). For wavelengths less than 0.7 pm, the MPE as calculated on the basis of n-rla also must not exceed the MPE calculated for nt seconds when nt is grcater than l0 s. For pulse repetition frequencies greater than 15 kHz, the average irradiance or radiant exposurc (radiance or integrated radiance) of the pulse rain shall not exceed the MPE (as given in 8.2) for a single pulse equal in duration to the pulse train duration, T' For wavelengths between 0.4 and 0.7 pm, the aversion response time, 0,25 s, may be used unless purposeful staring into the b€am is intended or antici' pated. For wavelengths greater than 0.7 pm, lOs may be used as the exposure duration unless purposeful staring into the beam is intended or anticipated. 8.3 MPE for Extended-Source Viewing. MPE values for ocular exposure to extended sources for single pulses or exposures are given in Table 6. All values are specified at the comea. (See 8.5 for special qualificalions and use; see also Figs.5,6, and 7.) For multiple pulse lasers or exposures, the MPE is deter' mined using the exposure time of the pulse train duration, 7' 8,4 MPE for Skin Exposure to a Laser Beam. MPE values for skin exposure to a laser beam are given in Table 7. These levels arc for worst-case conditions and are based on the best available informanon. E.4,1 MPE for Skin, Repeated Exposures For repetitive-pulsed lasers the MPEs for skin exposurc are applied as follows: Exposure of the skin shall not exceed the MPE based upon a single-pulse exposure, and the average irradiance of the pulse train shall not exceed the MPE applicable for the total pulse train, duration I. (See 8.5 for special qualifications and uses.) E.4.2 Wavelengths Greater than 1.4 lrm. For b€am cross-sectional areas between 100 cm' and 1000 cm2, the MPE for exposure durations exceeding
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o APPENDIX 't6 UJ (L d F x 9 J (r l
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APPENDIX 7lr SYMBOL AND BORDER. BLA
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APPENDIX D3. Safety Committee D3.l
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APPENDIX 82 Table Dl Recomrnended T
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APPENDIX been linked to working wit
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APPENDIX F2. Cryogenic Liquids Cryo
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APPENDIX simple heat flow models aP
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o APPENDIX Goldman, L., Rockwell, R
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Table l0 Control Measures for the F
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