Document 65j6QJLzpqeNJy6yBM621x1X4

cupational Exposure Limits For Novel Work Schedules R. S. BRIEF and R. A. SCALA Exxon Corporation, Medical Depi., Research aFd Environmental Health Division, Linden, New Jersey,07036 Work schedules other than 7 to 8 hr/day and 40 hr/week are being introduced in many industrial operations. Novel work schedules, such as four 10-hour workdays per week or three 12-hour workdays per week for three weeks followed by four 12-hour workdays for three weeks and several other plans are presently being used. The Threshold Limit Values ("LV)do not apply to such novel schedules. Modified occupational l i i t s , which are calculable from the methods suggeaed in this report, estimate the needed reduction in the TLV to provide protection for exposed workers. A simple system is suggested, but should be cautiously applied with good medical surveillance. Industrial hygiene experience with novel work schedules will ultimately provide the real requirements for acceptable exposures under such work conditions. HE PREFACE OF THE Limit (TLv)' es that the TLvs "represent conditions er which it is believed that nearly all kers may be repeatedly exposed day day without adverse effect'"The er to "time-weighted concentrations for s7-or 8-hour workday and a 40-hour work- e e e k . " In their recent recommended stand- e d for occupational exposure to inorganic G e n i c , the National Institute for Occupa- sIlop,n a l Safety and Health2 proposed a time- ighted average (TWA) limit for up to a -hour workday, 40-hour workmeek. In many industrial operations, novel work edules have been introduced in recent rs. These may come about to permit more cient use of manpower, to conserve ener- and in remote locations, to permit ade- e time off the job. Among the novel dules are: four 10-hour workdays per , a 6-week cycle of three 12-hour days for three weeks followed by four hour workdays for three weeks, a 56/21 de involving 56 continuous days of of 8 hours per day followed by 21 off, a 14/7 schedule involving 14 con- uous days of work of 8 to 12 hours per ay followed by 7 days off, and various modifications or combinations of these. In February 1974, we contacted the Chair- man of the ACGIH TLV Committee who indicated that they had set no exposure standards for novel work schedules nor had they evolved any ,approach to this issue. In light of the obvious need for these modified n v s , we have prepared some pre- liminary calculations and recommendations for novel work schedules. Basic Premise Whenever novel work schedules are utilized an uncertainty exists concerning the effects of exposure to chemical agents. The modified cmupational limits, which are calculzble from the methods suggested in this report, estimate the needed reduction in the TLV to provide protection for the exposed workers. However, these reduced limits are no guarantee that .anadequate safety margin will have been achieved. Therefore, we suooest that close medical surveillance be YV maintained for some reasonable period until it is assured that the modified limits do indeed protect the workers. The TLV must be reduced by some amount to take into account not only the increased hours of exposure per day but also the decreased hours of recovery. This will be expressed as the product of each factor 4 67 ND?lCE: Vhla n?a?a~iam! y h3 prmsc?a by copyrl$-$t b 3 {TiPisf 7, ilni?a21SWk5 cmtq; . -1 . -.*. 468 calculated for a workday. Reduction of TLV = effect of increased exposure time X effect of decreased exposure-free time TLV Reduction Factor (RF) = -8 h x -241-6 h h = hours worked per day The RF value should be applied (a) to TLVs expressed as a time-weighted average with respect to the mean and permissible excursion and (b) to TLVs which have a C (ceiling) notation except where the C nota- tion is based solely on sensory irritation. In this case the irritation response thresh- old is not likely to be altered downward by an increase in number of hours worked and modification of the TLV is not needed. Conditions The basis for the TLV of each chemical must be considered in the application of the TLV Reduction Factor. (1) Where the TLV is based on systemic effect (acute or chronic), the TLV reduction factor will be applied and the reduced TLV will be considered as a time-weighted average (TWA). Acute responses are viewed as falling into two categories: (a) rapid with immediate onset and (b) manifest with time during a single exposure. The former are guarded by the C notation and the latter are presumed time and concentration dependent and hence, are amenable to the modifications proposed. Number of days worked per week is not considered, except for a 7-day workweek discussed later. (2) Excursion factors for TWA limits (Appendix D of 1974 TLV publication) will.be +reduced according to the following equation: EF = [(EFs - l ) R F 11 where EF = desired excursion factor EF3 := value in Appendix D for 8- . hour T4WA RF = TLV Reduction Factor (3) Special case of 7-day workweek. Determine the TLV Reduction Factor based on exposure hours per week and exposure-free hours per week. (4) When the novel work schedule invo 24-hour continuous exposure, such as in- submerged habiiat or other totally enclosed2 environment designed for living and w o r k 3 ing, the TLV reduction technique cannot used. In such cases, the 90-day continu exposure limits of the National Acade of Science3 should be used, where appli limits apply. (5) The techniques are not applica work schedules less than seven to eigh per day or 35 hours per week. Sample Calculations (1) For a 6-week schedule of three 12 workdays for three weeks followed by 12-hour workdays for three weeks, should the new TLV be for methanol? TLV = 200ppm) ==-8 12 x 2 4 - 12 16 = 0.5 NewTLV = RF X TLV = 0.5 X 200ppm = l00ppm Note: The TLV Reduction Factor -., erican Industrial Hygiene Association Jburnal Exposure hours per week = 8 X 7 -- = 56 hrs. . Zxposure-free hours per week = (24 X 7) ;. - 56 = 112hr. - -40 56 x --11-2 128 - .625 ,NewTLV = RF X TLV = .6125X 10 ppm = 6ppm. ) For an 11-hour per day exposure, 4 lys per week what should the new TLV : for benzene? (1974 TLV = 25 C ppm) nce the C notation has been assigned to :nzene because of its chronic toxicity and It because of irritation, the TLV Reducin Factor approach can be used. The ;kin" notation in the TLV table signals le contribution of the cutaneous route to rerall benzene exposure. - -8 - x 11 2 41-611. = 0.6 New TLV = 0.6 X 25 = 15 C ppm. In summary, novel work schedules are :coming more common and widespread. ccupational exposure limits developed for to 8 hours per day and 5-day workweeks :ed to be modified to meet the differing c.ork-rest situations. A simple system is sugBested, but should be cautiously applied $Eiut* h good medical surveillance. Industrial pygiene experience with novel work schedWes will ultimately provide the real requireLents for acceptable exposures under such S o r k conditions. The authors welcome comments and hope 5 develop a useful dialogue among inter;ted and knowledgeable individuals. .eferences . Threshold Limits Committee: Threshold Lim- it Values for Chemical Substances in ihe Workroom Air Adopted b y ACGlH for 1974.American Conference of Governmental Industrial rgienists, P.O. Box 193 7, Cincinnati, Ohio 201 (197`4). ' --:c r i t e r i a f(or a Recommended 5.. Slandard-OccupationaI Exposure IOlnorganic & Arsenic. U.S. DHEW, National Institute for .:: Occupational Safety and Health, Rockville, Md. (1973). 469 3; : Atmospheric Contaminants in Spacecraft. Report of the Panel on Air Stand- ards for Manned Space Flight. Space Science Board, National Academy of Sciences, Washington, D.C. (October 1969) 86 p. Comments On "Occupational Exposure Limits For Novel Work Schedules" The proposal by Brief and Scala to adjust the TLVs according to vaned work schedules is very much in order, particularly for those substances with a small TLV safety factor, and when there is large departure from the seven- to eight-hour work schedule. Certainly, some such stopgap procedure is needed in the absence of any toxicologic information that has been tailored to particular work schedules. And even more so, when it is realized that the development of toxicologic criteria for all the permutations and combinations of work schedules for the 600 or so industrial substances with TLVs is an utter impossibility. But, at the same time, it should be recognized that the general formula approach is a first approximation only, guarantees no exact solution. Brief and Scala have recognized this, and have pointed out the necessity for cautious application of the formulae with appropriate medical surveillance. With such surveillance, information will accumulate that, in turn, will permit the development of firmly based TLVs. A limited amount of toxicologic information does exist on a few industria1 substances for the extreme case of continuous (24 hours/day, round-the-clock) exposures. This information unquestionably supports the need for TLV reduction for increased exposure periods; some substances that are well tolerated under TLV conditions, suddenly become lethal or near lethal when exposure at the TLV is continuous. In addition, the data clearIy show that not all substances behave in this manner, and that the TLV for some is satisfactory without adjustment even for continuous exposure. In these instances, the use of the reduction factor will obviously add an increased safety factor. .-- -