Patty's Industrial Hygiene, Physical and Biological Agents. Группа авторов

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      h, hour; s, second.

      4.3.2 Lamp Classifications

      Radiation‐emitting devices, including optical radiation sources, are subject to regulation in the United States by the U.S. Food and Drug Administration (FDA) through its Center for Devices and Radiological Health. The FDA has not established a classification system, analogous to its laser classification system, for noncoherent optical radiation sources.

      In the absence of governmental regulations requiring safety‐related classification of all lamps, the IESNA has published a voluntary guideline, ANSI/IES RP‐27.3, Recommended Practice for Photobiological Safety for Lamps and Lamps Systems – Risk Group Classification and Labeling (44). This recommended practice applies to all electrically powered sources emitting radiation between 200 and 3000 nm, except for LEDs used in fiber optic communications systems and lasers. Laser‐driven broadband light sources are included under the standard.

Under the RP‐27.3 recommended practice, the lamp manufacturer should evaluate the lamp for potential to exceed exposure guidelines for UV hazards, blue‐light hazard, IR‐corneal/lens hazard, and retinal thermal hazards. The spectral weighting functions and exposure limits are similar to current ACGIH guidelines (13, 18). An exception is the retinal thermal hazard for IR sources with weak visual stimulus, where the RP‐27.3 recommended practice uses an unweighted radiance. Based on these evaluations, a lamp is classified into one of four risk groups (RGs) – Exempt Group, RG 1 (very low risk), RG 2 (low risk), and RG 3 (high risk) – based on the potential for exceeding an exposure limit for one of these hazards within specified exposure durations. The criteria for RG classification are summarized in Table 2. The manufacturer is required to label packaging for lamps classified as RG‐1, RG‐2, and RG‐3 with appropriate statements prescribed in the RP‐27.3 recommended practice, including instructions on limiting the duration of exposure to the lamp and information that the lamp emits UV or IR radiation.

      In a global context, the International Electrotechnical Commission's IEC 62471:2006 standard, which was based on the ANSI/IES RP‐27 standards, has been adopted as a regulatory requirement by the European Union (EU) and other countries and has also been widely implemented on a voluntary basis by manufacturers of non‐laser light sources.

5 OPTICAL RADIATION CONTROL PRINCIPLES

      Traditionally, radiation control principles have been summarized under the rubric of “time, distance, and shielding.” “Time” as a control principle refers to reducing risk by limiting the duration of exposure to the radiation. “Distance” refers to the reduction in risk associated with increasing the distance from the source. “Shielding” refers to the presence of an opaque or filtering medium between the source and the worker.

      An additional control principle to consider is source optimization. Optimizing a source would include operating a source at the lowest power necessary to do the job, and, if possible, selecting sources with reduced spectral output in the blue‐light, UV‐A, UV‐B, and/or UV‐C regions if these wavelengths are not needed for the practical application.

      5.1 Exposure Duration

      For actinic UV radiation, the maximum permissible exposure time is (15)

(24)

where E_eff (in W m⁻²) is defined in Eq. (10). The maximum permissible exposure time for blue‐light sources that subtend an angle greater than 0.011 rad is (20):

      (25)

      and the maximum permissible exposure time for blue‐light sources that subtend an angle less than 0.011 rad is (20):

      (26)

      Unlike the photochemical effects represented by the actinic UV hazard and the blue‐light hazard, thermal effects do not show a strictly reciprocal relationship between spectrally weighted irradiance or radiance and permissible exposure time. Viewing durations may be limited involuntarily to a few seconds by the aversion response or the sensation of pain. A worker performing a visual task might, however, be motivated to persist in viewing an excessively bright source despite eye discomfort.

      5.2 Exposure Geometry

      5.2.1 Direction of Irradiation

      When possible, potentially hazardous optical radiation sources should be located out of the line of sight of workers. UV sources, which may pose a hazard to the skin as well as the eyes, should be oriented to avoid direct irradiation of exposed skin. An example is the use of upper room germicidal UV radiation, where germicidal lamps are positioned and baffled so as to flood the unoccupied upper space of a room with UV‐C radiation while limiting the amount of reflected or stray radiation that reaches the lowest 2 m (6.5 ft) of the room (45).

      If a surface directly irradiated by a hazardous optical radiation source is capable of reflecting radiation into a worker's eye, or onto exposed skin in the case of UV radiation, that surface should be treated with a matte or absorptive finish.

      5.2.2 СКАЧАТЬ