Document MGe3gBvNoKw7b10YwkZpv6JJy

1105 When the daily noise exposure is com posed of two or more periods of noise ex posure of different levels, their combined effect should be considered, rather than the individual effect of each If the sum of the following fractions. exceeds unity, then, the mixed exposure should be considered to exceed the thresh old limit value, Ci indicates the total time of exposure at a specified noise level, and Ti indicates the total time of exposure permitted at that level Noise exposures of less than 90 dBA do not enter mto the above calculations Impulse or impact noise It is recommended that exposure to im pulsive or impact noise should not exceed 140 decibels peak sound pressure level Ultraviolet Radiation* These threshold limit values refer to ultraviolet radiation tn the spectral region between 200 and 400 nm and represent conditions under which it is believed that nearly all workers may be repeatedly ex posed without adverse effect These values for exposure of the eye or die skin apply to ultraviolet radiation from arcs, gas, and vapor discharges, fluorescent, and incandescent sources, but do not apply to ultraviolet lasers09 or solar radiation These levels should not be used for de termining exposure of photosensitive in dividuals to ultraviolet radiation These values should be used as guides m die con trol of exposure to continuous sources where the exposure duration shall not be less than 0 1 sec These values should be used as guides in the control of exposure to ultraviolet sources and should not be regarded as a fine line between safe and dangerous levels Recommended values The threshold limit value for occupa tional exposure to ultraviolet radiation incident upon skin or eye where trradiance values are known and exposure time is controlled are as follows 1 For the near ultraviolet spectral region (320 to 400 mm) total irradiance in cident upon the unprotected skin or eye should not exceed I mw/cm2 for peri ods greater than 10* seconds (approxi mately 16 minutes) and for exposure times less than 103 seconds should not exceed one J/cm* 2 For the actimc ultraviolet spectral re gion (200-315 nm), radiant exposure incident upon the unprotected skin or eye should not exceed the values given in Table 8 within an 8-hour period 3 To determine the effective irradiance of a broadband source weighted against the peak of the spectral effectiveness curve (270 nm), the following weight ing formula should be used E<// *= 2! Ex Sx Ax where // = effective irradiance relative to a monochromatic source at 270 nm Ex ** spectral irradiance in W/cmynm Sx a relative spectral effectiveness (unitless) Ax 1=3 band width in nanometera 4 Permissible exposure time in seconds for exposure to actinic ultraviolet radiation incident upon the unprotected skin or eye may be computed by dividing 0 003 J/cm2 by E.rr in W/cm2 The exposure time may also be determined using Table 9 which provides exposure times corresponding to effective uradiances m MW/cm2 TABLE 6 RELATIVE SPECTRAL EFFECTIVENESS BY WAVE LENGTH Wavelength TLV (nm) (mj/cm2) 200 100 210 40 220 25 230 16 240 10 250 70 254 60 260 46 270 30 280 34 290 47 300 10 305 50 310 200 315 1000 Relative Spectral Effectiveness s* 003 0 075 012 019 030 043 05 085 10 088 084 0 30 008 0 015 0 003 * See Notice of Intended Changes, Page 1106 See Laser TLV