THIRD EDITION

INDUSTRIAL-OCCUPATIONALHYGIENE CALCULATIONS:

A Professional Reference

James H Stewart Ph.D., C.I.H., CSPRobert F Herrick, Sc.D., C.I.H.Martin Horowitz, C.I.H., CSP

Industrial-Occupational Hygiene Calculations:A Professional Reference

Third Edition, 2017

James H. Stewart, Ph.D, CIH, CSP Editor

Authors

James H. Stewart, Ph.D, CIH, CSPRobert F Herrick, Sc.D., CIHMartin Horowitz, CIH, CSP

Copyright, 2017 Millenium Associates

Industrial-Occupational Hygiene Calculations: A Professional Reference, Third Edition

Copyright © 2017 by Millennium Associates. All rights reserved. Printed in the United States of America.

Previous editions Copyright © Millennium Associates 1999 and 2005.

Except as permitted under the Copyright Act of 1976, no part of this book may be reproduced or distributed in any form or by any means, or stored in any database or retrieval system, without prior written permission

of the publisher.

Information contained in this work has been obtained by Millennium Associates from sources believed to be reliable. However, neither Millennium Associates or its authors guarantee the accuracy or completeness of any information published herein, and neither Millennium Associates nor its authors shall be responsible for any errors, omissions, or damages arising out of the use of this information. This work is published with the understanding that Millennium Associates and its authors are supplying information, but not attempting

to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. Nor will use of this work guarantee passing an industrial or

occupational hygiene professional certification examination.

Library of Congress Cataloging-in-Publication Data

Industrial-Occupational Hygiene and Safety Calculations: A Professional Reference, Third Edition Stewart, James Henry 2017

p. cm.Includes bibliographical references and index.

ISBN: 978-0-9671934-6-5

1. Industrial Hygiene 2. Occupational Hygiene 3. Calculations I. Stewart, James H.

Table of Contents

Section 1: Noise

Sound Pressure Level......................................................................................1

Sound Intensity Level.....................................................................................2

Distance and Sound Pressure Level.............................................................3

Adding Sound Pressure Levels.....................................................................4

Total Sound Pressure Level: n Identical Sources......................................5

Total Sound Pressure Level: Two Sources.................................................6

Total Sound Pressure Level...........................................................................7

Leq Equivalent Sound Pressure Level..........................................................8

Percent (%) Dose (Noise)...............................................................................9

Sound Pressure Level and Sound Power (English).................................10

Sound Pressure Level and Sound Power (metric)....................................11

Directivity Index (DI)..................................................................................12

Allowed Noise Exposure Time...................................................................13

TWAeqCalculated from % Dose (PEL)......................................................14

TWAeqCalculated from % Dose (TLV).....................................................15

Transmission Loss........................................................................................16

Frequency of Noise Produced by Fan........................................................17

Frequency and Wavelength.........................................................................18

Octave Bands: Upper and Lower Edge.....................................................19

0

or L 20logppSPLp

=

+=

2

1log2012

d

dSPLSPL

∑Ν

i=I= 1010log10

SPLi

fSPL

)1102 1

log ( 10101 +−

+=LL

LTotalL

1

1010log10

10

1

110log 10iLN

eq ii

L tT

=

= ∑

10log i

t

ETLE

10log( )f iSPL SPL n

( )( )60

N RPMf

cfλ

2 12f f=

Theory and Application Example

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Category:Noise

Terms and UnitsLPt = total sound pressure level generated by N sources (dB)LPi = individual sound pressure level of ith source (dB)N = number of sound pressure levels

Reference: Berger, E.H., et al., ed., 1986, Noise and Hearing Conservation Manual, American Industrial Hygiene Association (AIHA), Virginia Page 29.

Three machines are going to be situated in close proximity. Given their individual sound pressure levels, LPi, of 78, 82, and 84 dB, what is the approximate total sound pressure level, LPt ?

The sound pressure levels of different noise sources can be added via the equation above. It is another quantitative version of familiar tables where you will find, e.g. that for a numerical difference of 2 to 4 dB, you add 2.0 dB to the higher noise level to determine the total noise level.

The equation is used at the design stage to estimate noise levels post construction and to evaluate the efficacy of purchasing low noise machinery. Adding noise sources to an existing noise environment is another useful application.

Another application of this equation is to octave band measurements. The separate dB levels at each octave band can be added:

Octave Band dB level

31.5 8863 90125 92250 92500 951000 962000 924000 908000 88

Using the equation above to add these example octave band values will yield a noise total sound pressure level of 101.8 dB.

1

1010log10

Total Sound Pressure Level

78 82 8410 10 10

pt

pt

L = 10 log 10 +10 +10

L = 86.7dB

Theory and Application Example

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Category:General Sciences, Statistics, Standards

Terms and UnitsRF = reduction factor (unitless decimal)h = number of hours worked in a day

Reference: Klonne, DR : Occupational Exposure Limits. In AIHA, 2003, The Occupational Environment Its Eval-uation and Control, and Management, Dinardi, S editor, AIHA, Fairfax, VA , p 67. and Brief, R.S., and R.A. Scala, Occupational exposure limits for novel work schedules. Am.Ind. Hyg. Assoc. J. 36:467–469 (1975).

Occupational exposure limits like TLVs, PELs and RELs are usually developed for an 8-10 hour per day worker who in one one week would work 40 hours. The number of hours worked in a day or in a week directly impacts the “recovery” time, i.e., the time away from the exposure. During this time the worker’s body can detoxify and/or excrete the toxicant. If the occupational exposure limit was de-veloped with the assumption of 8 hours of exposure and 16 hours of recovery time then working more than 8 hours at the specified occupational exposure limit may not provide enough recovery time before going back into the work environment.

Brief and Scala, 1975 developed a method of ad-justing the occupational exposure limit for unusual work schedules. One equation adjusts for hours worked in a day, the other adjusts for hours worked in a week. The calculation is conservative, i.e., it provides a more protective result than other cur-rently available methods of accounting for unusual work schedules. As you can see in the formula as the number of hours increases the reduction factor (RF) decreases. The reduction factor is multiplied by the occupational exposure limit to obtain the “adusted occupational exposure limit”.

Adjusting for Unusual Work Schedules(hrs/day)

A worker is assigned to job that requires working 10 hours in a day. The worker is exposed to xylene. The TLV for toluene is 188 mg/m3. What is the adjusted TLV for this worker using the Brief and Scala method?

Since the TLV for xylene is 188 mg/m3 and the re-duction factor is 0.7 the worker can only be exposed to 132 mg/m3 for the 10 hour workday.

8 24-hRF= xh 168 24-10RF= x

10 1614RF=0.8 x16

RF=0.7

8 24-hRF= xh 16

8 24 -16

hRF xh

=

Theory and Application Example

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Category:Heat Stress

Terms and UnitsWBGT = wet bulb globe temperature (⋅F; ⋅C)tnwb = natural wet bulb temperature (⋅F; ⋅C)tg = globe temperature (⋅F; ⋅C)tdb = dry bulb temperature (⋅F; ⋅C)

Reference: NIOSH, Occupational Exposure to Heat and Hot Enviornments, NIOSH, Cincinnati, OH 2016, p 113; Larranaga, M.D, Thermal Standards and Measurement Techniques, In The Occupational Environment – Its Evaluation, Control and Management. 3rd Edition. Anna, D. ed., Fairfax, VA: AIHA, 2013, p. 929.

What was the WBGT reading at on outside con-struction site on a sunny day if the natural wet bulb measured 83 ºF, the globe temperature was 93 ºF and the dry bulb temperature was 91 ºF?

Heat stress is the environment the worker is in while heat strain is the physiological response to the heat stress. Many factors can influence an individual’s heat strain. These include age, physical condition, overall health, medications, ambient conditions (temperature, humidity, air movement), degree of acclimatization, and degree of physical exer-tion. The most effective means of evaluating heat buildup in the body is to measure deep body (core) temperature. Since this is not usually practical or acceptable to do in the work environment, exposure indices have been developed to asses heat stress. For workers, the Wet Bulb Globe Temperature In-dex (WBGT), as described in the ACGIH Threshold Limit Values publication, is the most commonly used measure of heat stress. Limits are based on the work:rest regimen, and on the physical level of the work. Further adjustments are made for type of clothing worn

This equation describes the relationship between the natural wet bulb temperature (tnwb), the globe temperature (tg), and the dry bulb temperature(tdb) for computing the Wet Bulb Globe Temperature (WBGT) Index for work outside on a sunny day or where there are radiant heat sources such as hot machinery. All thermometers must have unrestricted airflow around them and not be shaded from the sun. The wick of the natural wet bulb must be kept wet with distilled water, and the globe thermometer must have a matte black finish.

t 0.1 + t 0.2 + t0.7 = WBGT dbgnwb

( ) ( ) ( )F 0.1 + F 0.2 + F0.7 = WBGT 919383

FWBGT 86=

º º º

º

WBGT with Solar Load

0.7 0.2 0.1nwb g dbWBGT t t t= + +

Theory and Application Example

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Category:Ventilation

Terms and UnitsQ = volumetric flow rate (m3/s) A = area of the duct (m2) 1.29 = constant based on standard temperature and pressure SP = hood static pressure (Pa) Ce = hood entry coefficient (unitless)df = density factor with reference to standard air((unitless)

Reference: American Conference of Governmental Industrial Hygienists (ACGIH), Industrial Ventilation: A Manual of Recommended Practice For Design, 29th Ed. Cincinnati: ACGIH, 2016, p. 3-13

A static pressure tap was installed on an (15.24 cm diameter duct (A=0.0.0182 m2). The manometer read 498 Pa and the air density factor is 0.96. With a hood entry coefficient of 0.85 what was the flow rate of the hood?

Hood performance can vary over time due to obstructions within the duct, or possibly due to corroded or dirty fan blades. Therefore, a need exists for calculating the volumetric airflow into a hood opening for comparison to design specifications. This equation is sometimes referred to as the throat-suction equation, and can be used to determine the volumetric flow rate, Q, of air flowing into a hood by simply measuring the hood static pressure, SPh. The hood entry coefficient, Ce , is a constant for a given hood type, and is a measure of the overall efficiency of a hood in directing air into the hood and accelerating it to duct velocity. Since Ce, 1.29, and the duct area are all constants for a particular hood type, a simple measurement of the hood static pressure can quickly and easily yield the current volumetric flow rate. The density factor (df)is the ratio of the actual density of air divided by the density of standard air (1.204 kg/m3) at 21 ºCand 101 kPa).

The hood static pressure is generally measured at least three duct-diameters down stream from the hood (throat) opening through the use of a simple hood static pressure tap connected to an inclined manometer mounted outside the hood above the sash.

Hood Flow Rate and Static Pressure (Metric)

Theory and Application Example

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Category:Ionizing Radiation

Terms and UnitsX = thickness required, any convenient unitsHVL = thickness of half-value layer, same units as XI2 = intensity of attenuated radiation, same units as incident radiationI1 = intensity of incident radiation. Common units would be photons/cm2-sec, mR/hr, mrad/hr.

Reference: Shapiro, J., 1990, Radiation Protection: A Guide for Scientists and Physicians, third edition, Harvard University Press, Cambridge, MA, p115.

Calculate the thickness of lead required to reduce the exposure rate of a Cs-137 source at a point 1 ft from the source from 12 mR/hr to 0.852 mR/hr. The HVL in lead for the 0.6 MeV gamma radiation from Cs-137 is 0.5 cm.

This equation gives the thickness of medium re-quired to attenuate radiation from intensity I1 to In-tensity I2. The same type of equation can also deal with reductions in dose rate or exposure rate. The basis of the equation is that each half-value layer in a medium attenuates the radiation by a factor of 2, so n half-value layers will attenuate the radiation by a factor of 2n . The number of half-value layers is equal to the thickness of the attenuating medium divided by the thickness of a half-value layer, x/HVL. Thus, the attenuated radiation at thickness I2 = I1 / 2

x/HVL. This can also be written I1 /I2 = 2x/HVL.

The equation is solved for X by taking the log of both sides.

rearranging,

)2log

)((log

)

)2 (log

()log(

2

1

2

1

HVL

I

IX

HVL

X

I

I

=

=

2log

)log(2

1 HVLI

I

X =

cmX

cmX

cmX

cmhrmR

hrmR

X

9.1301.0

)5.0(149.1

2log

)5.0)(08.14log(

2log

)5.0)(/852.0

/0.12log(

=

=

=

=

Shield Thickness

Theory and Application Example

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Category:Non-Ionizing Radiation

Terms and UnitsDs = separation for barrier (cm)ø = emergent beam divergence (radians) Φ = total radiant power output (W)TL = threshold limit value of barrier (W/cm2)a = exit beam diameter (cm)

Reference: ANSI Z136.1, 2000, American National Standard for Safe Use of Lasers, American National Standards Institute (ANSI), New York, p 120.

Assuming a TL value of 30 W/cm2 for an 8 hour worst case exposure duration for a 250 W Class 4 laser with a beam divergence of 2 mrad and an exit beam diameter of 0.5 cm, what is the necessary separation distance, Ds?

This equation allows calculation of the minimum distance (Ds) or installation distance for a barrier to be sufficiently protective for a given laser. At a distance less than Ds, the beam may penetrate the barrier and cause a potential exposure hazard. Note that it takes the same form as the equation for nominal hazard zone but substitutes the threshold limit value of the barrier (TL) for the exposure limit (EL). As the beam diverges, the irradiance (W/cm2) decreases. As the emergent beam divergence (0) increases, the value of Ds, above, decreases since the irradiance of the beam as it reaches the barrier, is lower. In applying this equation to an individual situation, an 8-hour exposure may be assumed in picking the TL value for worst case application though 60 sec. is more frequently chosen. One type of barrier that is increasingly available is acrylic plastic windows that allow some visible wavelengths to penetrate but will have a significant optical density for the wavelength of the laser output. For all barriers, the material cannot be combustible at the worst case conditions present.

In many industrial laser tools, the laser is enclosed and interlocked so the tool, as a whole, is Class 1. When the tool is opened for servicing, open beam, class 3b or 4 conditions may develop. Then, use of portable barriers may be important. Those people who work inside the barrier must be trained and equipped with appropriate personal protection.

Acceptable Distance for Laser Barrier

12

2s

12

2s -3 2

s

1 4D = -aTL

1 4 x 250WD = - 0.52 x 10 rad 30 W/cm

D = 1609cm = 16m

φ π

π

Φ

12

21 4sD a

TLφ π Φ = −

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References

ACGIH, 2016, Industrial Ventilation: A Manual of Recommended Practice for Design, 29th Ed., American Conference of Governmental Industrial Hygienists (ACGIH), Cincinnati, Ohio.

ACGIH, 1998, Industrial Ventilation: A Manual of Recommended Practice for Design, 23rd Ed., American Conference of Governmental Industrial Hygienists (ACGIH), Cincinnati, Ohio.

ACGIH, 2016, TLVs and BEIs , American Conference of Governmental Industrial Hygienists (ACGIH), Cincinnati, Ohio.

AIHA, 2013 The Occupational Environment – Its Evaluation, Control and Management, Annd, D., ed. AIHA, Fairfax, VA

AIHA, 2003 The Occupational Environment – Its Evaluation, Control and Management, DiNardi,SR, ed. AIHA, Fairfax, VA

AIHA, 1997, The Occupational Environment – Its Evaluation and Control, edited by DiNardi, SR, Fairfax, VA

AIHA, 2009, Mathematical Exposure Models for Estimating Occupational Exposures to Chemicals, 2nd Edition, AIHA, Farifax, VA.

AIHA, 2015, A Strategy for Assessing and Managing Occupational Exposures, 4th edition, AIHA, Fairfax, VA.

ANSI Z136.1, 2000, American National Standard for Safe Use of Lasers, American National Standards Institute (ANSI), New York, New York.

NSC, 2012, Fundamentals of Industrial Hygiene, Plog, B.A. and Quinlan, P.J., editors Nation-al Safety Council, Itasca, Illinois

NIOSH, Criteria for a Recommended Standard for Occupational Exposure to Heat and Hot Enviorn-ments, NIOSH, Cincinnati, OH,

ANSI Z136.1, 2000, American National Standard for Safe Use of Lasers, American National Standards Institute (ANSI), New York.

Berger, E.H., et al., ed., 1986, Noise and Hearing Conservation Manual, American Industrial Hygiene Association (AIHA), Virginia.

Brauer, Roger L, 1990, Safety and Health for Engineers, Van Nostrand Reinhold, New York.

Colton, T. 1974, Statistics in Medicine, Little, Brown, Boston, MA.

DiNardi, S.R., 1995, Calculation Methods for Industrial Hygiene, Van Nostrand Reinhold, New York.

Dr. Stewart has served as a Plant, Division and Corporate Director/Manager of Environmental Health and Safety for several large multinational organi-zations/companies, and Director of Environmental Health and Safety for Harvard University and as well as a Compliance Officer (Industrial Hygienist) with U.S. OSHA. Dr. Stewart is certified in the Comprehensive Practice of Industrial Hygiene and is also a Certified Safety. Professional. He has many years of experience as an active member of the environmental health and safety profession. Dr. Stewart received his Ph.D. in Environmental Health/Toxicology (minor in Epidemiology) from the University of Massachusetts at Amherst in 1992. He also holds a Master’s degree in Chemistry and a Bachelor’s degree in Public Health. Dr. Stewart has served on two National Academy of Science Committees as an industrial hygiene and safety expert Dr. Stewart is a currently a Visiting Scientist (Instructor Ret.) at the Harvard T.H. Chan School of Public Health and a Senior Lecturer in Environmental Health

Robert Herrick’s educational background includes a BA degree in Chemistry from the College of Wooster, an MS in Environmental Health Science from the University of Michigan, and a Doctor of Science in Industrial Hygiene from the Harvard School of Public Health. He is certified in the comprehensive practice of industrial hygiene. His research interests are centered on the assessment of exposure as a cause of occupational and environmental disease. He has conducted research on the development of methods to measure the biologically active characteristics of reactive aerosols, and on studies of work processes in several industries to develop task-based models to identify and control the primary sources of worker exposures.

Dr. Herrick is Past Chair of the American Conference of Governmental Hygienists (ACGIH), and Past President of the International Occupational

Hygiene Association. He is currently a Fellow in the American Industrial Hygiene Association. Prior to joining the faculty at the Harvard School of Public Health, Dr. Herrick spent 17 years at the National Institute for Occupational Safety and Health (NIOSH) where he conducted occupational health research. He has served on advisory panels to the USEPA, the National Academy of Sciences, and NIOSH. Dr. Herrick has authored over 100 peer-reviewed publications.

Martin is a graduate of the Master’s Program at the Harvard School of Public Health with a degree in Industrial Hygiene. He spent 14 years at Polaroid Corp. in the Corporate Industrial Hygiene Office and Divisional Semiconductor Manufacturing Group. Duties included industrial hygiene monitoring and control evaluation, radiation and laser safety officer. Martin then worked at the Micromachined Products Div. of Analog Devices in Cambridge as the Health and Safety Manager. This included industrial hygiene, safety, and hazardous waste management at a semiconductor fabrication facility. He assisted in de-commissioning of the facility before moving to an EHS Engineering position in the Wilmington production facility. He holds the C.I.H. and CSP certifications. His special interests/expertise lie in the physical agents such as nonionizing radiation and noise as well as direct reading instruments.

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