1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
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4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR4964 AEROSPACE INFORMATION REPORT AIR4964 Issued 1998-03 Reaffirmed 2014-12 Ex
5、posure Levels of UV Radiation in Nondestructive Inspection Processes RATIONALE AIR4964 has been reaffirmed to comply with the SAE five-year review policy. INTRODUCTIONThe UV-A lamps (also known as blacklights) contain mercury-gas plasma that emit radiation specific to the mercury atomic transition s
6、pectrum. There are several discrete lines in the ultraviolet section of the electromagnetic spectrum (between 180 to 400 nm). The irradiance output is dependent on the gas pressure and the amount of mercury content. Higher values of these parameters result in significant increase in its UV emission.
7、 Blacklights used for NDT employ appropriate filters (integral or external to the light source) to minimize the visible light output (between 400 to 760 nm) vital to the fluorescent inspection processes. Furthermore, these filters also block any harmful radiation below 320 nm. Medical data suggests
8、that radiation between 180 to 319 nm (UV-B and UV-C) can cause severe skin and eye burns. the sensitivity of the skin to such radiation is a function of the incident UV wavelength and its dosage. Normally, the erythemal effectiveness is strong between 180 to 300 nm, with rapid fall-off to 1% at 320
9、nm. Therefore, the filter characteristics and the lamp head construction play an important role in the radiation safety and suitability of blacklights for the NDT industry.1. SCOPE:Long wave ultraviolet or UV-A radiation (between 320 to 400 nm) is used for fluorescent inspections in magnetic particl
10、e and liquid penetrant examinations. The UV-A radiation is obtained from either fluorescent or high intensity discharge lamps that are stationary or portable. The commercially available UV-A lamps possess a large variation in intensity output that can cause a legitimate concern for possible health h
11、azard. This draft reviews the nature of UV-A radiation emitted by these lights, blacklight equipment, acceptable UV dosage limits adopted by the American Conference of Governmental Industrial Hygienists (ACGIH) and the European Standards Committee for Nondestructive Testing, and recommendation of pr
12、oper practices when working with UV-A radiation.2. APPLICABLE DOCUMENTS:There are no referenced publications specified herein.3. BLACKLIGHT EQUIPMENT:The most commonly used blacklights are low, medium, or high-pressure mercury vapor discharge sources. The low pressure lamps are coated with special p
13、hosphor in order to maximize its UV-A output. The medium and high pressure lamps do not have phosphor coatings but operate at higher electrical power levels resulting in significantly higher UV-A output. Typically, the low pressure lamps are used in wash stations, whereas the medium or high pressure
14、 lamps are used in fluorescent inspection sites. Figures 1, 2, and 3 illustrate the emission profiles of such blacklights. A well-designed medium or high pressure blacklight should emit less than 0.25% and 1% of its total radiative output under 320 nm and above 400 nm, respectively. Spectroradiometr
15、ic measurements conducted by the manufacturers of blacklight equipment must conform to the desirable emission characteristics.4. UV-A AND VISIBLE LIGHT SPECIFICATIONS:The AMS, Military, ASTM and other industrial NDT specifications in the United States require a minimum working UV-A irradiance level
16、(measured with a suitable blacklight meter) of 1000 uW/cm2and a maximum permissible visible light level (measured with an illuminance meter with a CIE photopic spectral response) of 2 ft-c (20 lx) at the inspection surface. These values have also been adopted by the European NDT community. In additi
17、on, the European committee is working towards incorporating into their specification a maximum UV-A irradiance level of 5000 uW/cm2at the examination surface.The upper UV-A level was determined following penetrant indication experiments conducted on Nichrome test panels. The UV-A reflected from the
18、examination part reduced the contrast level when working with irradiance in excess of 5000 uW/cm2. Also, saturation effects of the fluorescent material were perceived at high irradiance levels. Presently, none of the U.S. specifications denote a maximum UV-A level, although it may be useful to incor
19、porate such a value. An upper limit could improve the inspection process and certainly pose less health-hazard.5. THRESHOLD LIMIT VALUES FOR UV-A EXPOSURE:The American Conference of Governmental Industrial Hygienists (ACGIH) recommends threshold limit values (TLVs) for UV radiation in the spectral r
20、egion between 180 to 400 nm. These values represent conditions under which it is believed that nearly all workers may be repeatedly exposed without adverse health effects. For the long wave UV spectral region (UV-A), the total irradiance incident upon the unprotected eye should not exceed 1 mW/cm2(1
21、000 uW/cm2) for periods greater than 1000 s (approximately 16 min). For exposure times less than 1000 s, the total UV-A dosage should not exceed 1 J/cm2(Joule = Watts x seconds). However, these values do not apply to photosensitive individuals or to individuals concomitantly exposed to photosensitiz
22、ing agents such as special medication. Such individuals must seek doctors advice prior to further UV exposure. The TLV for occupational exposure to UV-A radiation within an 8-h period should be used as a guide and not be regarded as a fine line between safe and dangerous levels.SAE INTERNATIONAL AIR
23、4964 2 OF 7FIGURE 1 - Spectral Power Output of a Low-Pressure Mercury Vapor BlacklightSAE INTERNATIONAL AIR4964 3 OF 7FIGURE 2 - Spectral Power Output of a Medium-Pressure Mercury Vapor BlacklightSAE INTERNATIONAL AIR4964 4 OF 7FIGURE 3 - Spectral Power Output of a High-Pressure Mercury Vapor Blackl
24、ightSAE INTERNATIONAL AIR4964 5 OF 76. RECOMMENDED PRACTICES WHEN WORKING WITH BLACKLIGHTS:Although UV-A radiation is known to be relatively safe compared to UV-B or UV-C radiation, it is necessary that all operators and supervisors observe certain safety precautions. Personnel using UV-A lamps or b
25、lacklights should avoid looking directly at the sources with naked eye. This could cause ocular fluorescence and consequently lower the users ability to detect an indication. The blacklight filter must always be maintained in good condition and free from cracks, as radiation at wavelengths below 320
26、 nm is harmful. Most importantly, it is recommended that users wear non-photochromic eyewear (goggles or spectacles) when performing inspection. The eyewear should be made of clear optical material (not tinted) and possess UV-blocking capabilities - better than 10-4in the180 to 400 nm region. Figure
27、 4 shows the transmission characteristics of such eyewear. Finally, as a matter of good practice, it is desirable that the user wear long-sleeve clothing and minimize direct exposure of radiation to the skin.SAE INTERNATIONAL AIR4964 6 OF 7FIGURE 4 - Transmission Curve of UV-Blocking EyewearPREPARED BY AMS COMMITTEE “K”SAE INTERNATIONAL AIR4964 7 OF 7
