Industrial Hygiene Concepts

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1 This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. Your use of this material constitutes acceptance of that license and the conditions of use of materials on this site. Copyright 2006, The Johns Hopkins University, Patrick Breysse, and Peter S. J. Lees. All rights reserved. Use of these materials permitted only in accordance with license rights granted. Materials provided AS IS ; no representations or warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for obtaining permissions for use from third parties as needed.

Copyright 2006, The Johns Hopkins University, Patrick Breysse, and Peter S. J. Lees. All rights reserved.

2 Industrial Hygiene Concepts Patrick N. Breysse, PhD, CIH Peter S.J. Lees, PhD, CIH Johns Hopkins University Copyright 2005, Patrick N. Breysse, Peter S. J. Lees, and The Johns Hopkins University. All rights reserved. Use of these materials permitted only in accordance with license rights granted. Materials provided AS IS ; no representations or warranties provided. User assumes all responsibility for use, and all liability related thereto, and must independently review all materials for accuracy and efficacy. May contain materials owned by others. User is responsible for obtaining permissions for use from third parties as needed.

Materials provided AS IS ; no representations or warranties provided.

3 Section A Time-Weighted Averages

4 Exposure Profile CONCENTRATION Time weighted average (TWA) Peak 2 0 8:00 9:00 10:00 11:00 12:00 1:00 2:00 3:00 4:00 5:00 TIME Source: Patrick Breysse and Peter S. J. Lees 4

5 Time-Weighted Average Apportions the measured exposure based on the interval of time during which the exposure occurred Can apply to any time period but is typically used for 8-hour periods of time Also applies to short term samples (i.e., a STEL is a 15-minute TWA) 5

to any time period but is typically used for 8-hour periods of

6 Calculation of Time-Weighted Averages General formula: TWA where : c t i i n i 1 n c i 1 1 t t concentration during the i duration of i 1 the i th interval th interval Continued 6

7 Calculation of Time-Weighted Averages Common formula: TWA t 1 c1 t t1 c2... t t2... tn 2 n c n Compliance formula: 8hr TWA t c t c2... 8hr t n c n 7

8 Example of TWA Calculation Partial period samples (PEL12ppm): 4 11ppm 2 14ppm 2 hours@ 20ppm TWA 4hr 11ppm 2hr 14ppm 2hr 20ppm 4hr 2hr 2hr Continued 8

9 Example of TWA Calculation TWA 44ppmhr 28ppmhr 8hr 40ppmhr 112ppmhr TWA 8hr 14ppm Continued 9

10 Example of TWA Calculation Partial period samples: 1 11ppm 2 14ppm TWA 1hr 11ppm 1hr 2hr 2hr 14ppm Continued 10

11 Example of TWA Calculation TWA 11ppmhr 28ppmhr 3hr 39ppmhr 3 - Hour TWA 3hr 13ppm 11

12 Compliance and the 8-Hour TWA Partial period samples (PEL12ppm): 4 11ppm 2 14ppm 2 hours@ not sampled TWA 4hr 11ppm 2hr 14ppm 2hr 0ppm 4hr 2hr 2hr Continued 12

2 hours @ 14ppm 2 hours@ not sampled TWA

13 Compliance and the 8-Hour TWA TWA 44ppmhr 28ppmhr 8hr 0ppmhr 72ppmhr 8 - Hour TWA 8hr 9ppm 13

14 Section B Exposure Limits for Mixtures

15 Exposure Limits (ELs) for Mixtures Exposure limits set for single substances, but multiple simultaneous exposures is the industrial norm Combined exposure limit can be calculated if: Components have similar toxicological effects Combined effect is assumed to be additive 15

norm Combined exposure limit can be calculated if: Components have

16 Calculating EL for Mixtures Mixture in compliance if: C EL 1 1 C EL C EL n n < 1.0 where : C measured 8 - hour TWA concentration EL exposure limit for substance 16

17 Example of EL for Mixtures Mixture: Methyl isopropyl 100 ppm (TLV200ppm) 300ppm (TLV400ppm) Both TLVs set for protection against anesthetic (CNS) effects Continued 17

Methylcyclohexane @ 300ppm (TLV400ppm) Both TLVs

18 Example of EL for Mixtures 100ppm 200ppm 300ppm 400ppm which is not less than 1.0, so this mixture is NOT in compliance 18

19 Section C Exposure Limits for Extended Work Shifts

20 EL for > 8-Hour Work Shifts Many workers work longer than eight hours per day and 40 hours per week Apply adjustments to ELs with caution Should not be used to justify very high exposures as allowable where exposure periods are short Continued 20

to ELs with caution Should not be used to justify very high

21 EL for > 8-Hour Work Shifts Adjustments don t have the benefit of historical use and long term observation Medical supervision during early adjustment use advisable Continued 21

22 EL for > 8-Hour Work Shifts In simplest form, dose (concentration x time) is held constant and new allowable concentration is calculated: C allowedt8hr C allowed T Xhr Other more complicated adjustment calculations can account for pharmacokinetic behavior 22

23 Example EL for >8-Hour Work Shifts What is the EL for benzene over a 12-hour shift given an 8-hour EL of 1.0ppm? C allowed T 8hr C allowed T Xhr 1.0ppm 8hr Xppm 12hr 8.0ppmhr 12Xppmhr X 0.67ppm 23

Principles of Ventilation. Patrick N. Breysse, PhD, CIH Peter S.J. Lees, PhD, CIH Johns Hopkins University

Principles of Ventilation. Patrick N. Breysse, PhD, CIH Peter S.J. Lees, PhD, CIH Johns Hopkins University This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. Your use of this material constitutes acceptance of that license and the conditions of use of materials on this