A Review of Damage Risk Contours for Occupational Noise Exposure

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PREPRINT NO. 905 (D-l)

A REVIEW OF DAMAGE RISK CONTOURS FOR OCCUPATIONAL NOISE EXPOSURE

by

Alex J. Szecsody

Ar iz on a S tat e U niv er si ty

T em pe , A ri zo na

PRESENTED AT THE

45th CONVENTION

MAY 15-18, 1973

' , .... .

' , AN AUDIO ENGINEERING SOCIETY PREPRINT

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_) Copyright 1973by the Audio EngineeringSociety. All rights reserved.



A REVIEW OF DAMAGE RISK CONTOURS

FOR OCCUPATIONAL NOISE EXPOSURE

by

Alex J. Szecsody,

Graduate Student,

Arizona State University, Tempe, Arizona

Abstract

The past 22 years has seen the development of a number of

damage risk contours for occupational noise exposure. Historicalreliance has been made on the dB X subscript method for establish-

ing specifications. This paper reviews the state-of-the-art for

damage risk contours and finds serious inadequacies in such a

practiced methodology. Since some 57 million wage earners are now

covered by the 0ecupational Safety and Health Act (OSHA), the need

for a redefined damage risk contour is documented, especially, the

need to verify complex pure tones as the basic industrial noise

exposure for a number of contemporary industries.

Terminoloqv

Abbreviations:

NAS-NRC CHABA National Academy of Science-National Research

Working Group 46 Council, Committee on Hearing and Bioacous-

tics Working Group 46.

DRC Damage Risk Contours for Noise Exposure.

TTS Temporary Threshold Shift of Hearing.

PTS Permanent Threshold shift of Hearing.

NIPTS Noise Induced Permanent Threshold Shift.

AAOO American Academy of Ophthalmology and

Otolaryngology.

Terms:

NOISE Unwanted sound.

HEALTH "A state of complete physical, mental and

social well being and not merely an absence

of disease and infirmity."--World Health

Organization.

Occupational Exposures to noise as a statement of the

Noise Exposure environment in which an employee is occupa-

tionally employed.

Damage Risk A statistical term for noise exposure

Contour expressed as a function of time and spectra;usually associated with percentage of hear-

ing loss as a function of years of occupa-



PREFACE

" . . . and a large part of the confusion we have today in

hearing theories is a consequence of extrapolations. It is not a

usual custdm to describe a law with its range of validity simul-

taneously, since it is often more difficult to establish the range

of validity than the law itself. Therefore, extrapolation is a

common and accepted practice."

Georg Von Bekesy(1)

REVIEW OF CONTOURS OF EQUAL INTENSITY

Studies by Fletcher-Munson concerning equal loudness contoursare discussed in reference 2. The Fletcher-Munson equal loudness

contours consists of lines of equal loudness with frequency tones

varied and intensity held constant. The lines of equal loudness are

referred to as phon lines each with a unit value. Figure 1 is a

plot from the above reference of these equal loudness contours. A

study of figure 1 shows that the equal loudness contours flatten out

from i00 HZ to 1 KHZ as there is an increase from the 40 phons to

the 100 phons contour.

Kryter (3) introduces the term noisiness or noy as the value

from which equal contour noy lines are developed. The values of

noys are combined into a one number value termed Perceived Noise in

dB--namely, PndB. Figure 2 shows the noy contour lines as devel-

oped by Kryter.

The table which follows summarizes four current techniques

available to derive a one-number value of a noise spectra using con-

tour lines developed by each of four authors. These techniques are

in common use today and recognized computational standards are pro-

vided in the use of these contours.

Scale ComputationalCommon Name Author

ProcedureLinear Log

Equal loudness Fletcher-Munson Sone Phon ISO 131, 226

contour

Loudness Index Stevens Sone Phon ISO 532, Method A

Mark VI

Loudness Density Zwicker Sone/Bark Phon ISO 532, Method B

Perceived Noise Kryter PndB Noy ARP-865A

Each author recognizes contour lines for subjective hearing

response as a function of sound pressure level and frequency. Fur-

ther, each author indicates a general flattening out of the contour

lines from 20 HZ to 1 K_ as a function of an increase of sound pres-sure level (see figures 3, 4, 5, and 6.)



iu.: . ,_"_ _ .. _ _ _ :-'4 ......_-I-'-' :-!_ ..... _- _- --:_-:+_-i-'I... . " _::_,: _:-.!:-::-I:::':;-'-=-----:-=:_.=-_;-q+'-_;-;-I-I

, . _ :. _.: I .............. "......_-_I_• _ . . " :-. "........ .-- 'i_....-._..........:- .-- i,llc_--s_ :;--_:_I_t- ' , '-' - . " _'"''_:_-_ ...... - .<" --: ;_._-_;1

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Ftlture 1



Figure 2

-3 -



FAMILY OF COL_fOUR LINES

:)_'_,,_<._-__- _ o-"--.v<l-±v-I <: :oi-%_-_-_-_."--<-;_-_--.=---.."..-I

Fletcher-Munson _ , ,_=-o_,-=......Figure 3

S%evens - Mark Vl

Figure



Kr_ter

Figure 6

--A-



dB x - SUBSCRIPT METHOD

Although contours of equal intensity were useful laboratory tools, a definitive need

arose to relate the noise environment to some simple yet representative weighting scale.

The first such application was made in a noise survey for the city of New York in

the year 1930. Fletcher used A-30 sensation line for weighting the noise data from this

survey. It should be noted that the survey dealt primarily with the intrusiveness caused

by noise and not DRC for hearing conservation.

Recognizing the usefulness of a representative contour for a range of ordinate levels

of sound pressure level, three modified phon contour lines from the Fletcher-Munson curves

were selected for sound level meters. The subscript dBx was hence assigned an alphabet

value as follows:

Subscript dBA dBB dBC

Inverse contour line in phons 40 70 I00

Figure 7 presents the 40 phon contour modified to become the current dBA contour.

Note the extensive modeling from 2 KHZ to i0 KHZ which occurred to the 40 phon contour.

Figure 8 presents the inverse dBA contour which is used in weighting networks of sound

level meters and data processing equipment.

Having established the dB A contour, it is now possible to calculate a one-number

value for this contour when placed into some ordinate setting. For the purposes of this

paper, a level of 90 dBA and its 1 KHZ crossing point has been chosen to illustrate con-

trasts between other dB x contours since it represents a DRC for industrial workers.

Figure 9 is a replot of the Fletcher 30-sensation line and is plotted against the

90 dBA line using 1 KHZ as the point for coincident crossing.

The simplicity of the dB x method has not ended with the A, B, C's. Kryter has

selected from his equal noisiness contours the 40 noy line as a representative contour to

arrive at a one-number value of preceived noise expressed as dBD. Figure i0 presents

this 40 noy contour plotted against the 90 dBA contour together with the unmodified

original 40 phon contour. A study of this graph reveals a sharp difference between the

90 dBA contour and the 40 noy contour at all frequency values from the 1 KHZ intercept

point.

Figure ii presents the four weighting contours dBA, dBB, dB C and dB D as they are used

in determining the subjective value of a noise spectra. The noise spectra is attenuated

per tables established by standards organizations resulting in a new spectra. The area

under this new curve provides a one-number value which is expressed in dBA, dB B, dB C or

dBD. This one-number value is considered to correspond to the subjective response to noise.

It should be noted that the scale most prevalent in the industrially developed

countries is dB A and has been for a number of decades. As a result, many noise survey and

hearing conservation specifications have evolved a numberical value of dB A.

To complete the picture on the dB x method, Stevens (4) proposed the use of the ap-

proximate 20-sone contour to be used for a one-number dB E calculation. Figure 12 pre-

sents the Stevens 20=sone contour (dBE) plotted against the 90 dBA contour and the dB D

contours. Nevertheless, dB E contrasts sharply with dBA contour at frequency points away

from the 1 KHZ intercept.

-5 -





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Figure 8

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Figure 9



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t , : * Intercept for 40 phon and 40:.NOy

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-? -



X

S O

20 50 100 200 ,500 lo00 2000 5(xx_ 10,000 20,000

FREQUENCY (HzJ

in_rr_ion_ _n_ ,4. D, and C we_'_;r curv_ _r Jound_ rne_ A_ d_*m

k _ pra_ D w_i_'n 0 _,ar,_ for manimtlnf jwr _i_aD_



Figure 12

-8-



HISTORY OF DAMAGE RISK CONTOURS FROM 1950 TO 1964

The attempt to establish exposure limits to noise dates back in the U.S.A. a minimum

of 20 years. Figure 13 presents graphically DRC's for octave band sound pressure level

versus frequency exposure from 1950 to 1964. One conclusion drawn from Figure 13 is thedownward trend in permissible DRC's.

The first state to adopt a noise exposure DRC was the State of California (5). Itis interesting that ISO 1961 levels average i0 dB lower than the State of California

1962 Standards over the entire range of octave bands.

Figure 14 presents DRC's for narrow band exposure to noise. Significant is the

recognition of exposure to narrow band noise. Here again the downward trend is noted.

The reason for the downward trend may be a combination of three factors: (i) in-

creased knowledge and data concerning DRC's, (2) increased legislative effectiveness

from public/labor/medical/audiological groups, and (3) political/industrial legislativecompromises.

_i-- !I_ ........ FOR FULL

_ Figure 13

._ .... _". 2 -22-_2_ " . . ...

gz 4

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7_ ,_-: -_-.v_L--=_ _-_- _ _...... _--4-.-;' --_:_=_-_.---_---

lil , ' 05 : ,

-9-



HISTORY OF FEDERAL DAMAGE RISK CONTOURS

A public concern for industrial safety resulted in the passage of the Walsh-Healey

Act of 1934. This act extended provisions of industrial safety to employees of firms

under Federal contract for products in which the contract exceeded $i0,000.

In 1968, thirty-four years later, the first federal mention is made of noise for

industry. Quoting section 50-204.293, "Noise shall be reasonable reduced or eliminated

as a means of preventing fatigue or accidents." (6)

In 1970, these standards were extended to employees of firms engaged in interstate

commerce (8). Accordingly, some 57 million wage earners in 4.1 million establishments

throughout the United States are covered by this act. This act is referred to as the

Williams-Steiger Occupational Safety & Health Act of 1970 or by the alphabet term OSHA.

The provisions of the Walsh-HealyAct as they now apply to OSHA regarding occupa-

tional noise exposure are presented in Figure 15.

An earlier Federal Standard on Occupational Noise Exposure for personnel in military

service existed as early as 1957. This report is Air Force 160.1. Figure 8 of referenced

report presents DRC's for octave bands of noise and DRC's for pure tones and critical

bands of noise (8).

Walsh-HealeyPublicContractsAct " - "_ . . " ' .-. . :-.=.;.... " . : • , ":"_ =/./,,."AS _ from Safety. and Ilealth Standards, Federal RotOr=c, _ ! , _

" 35, 7946-7954 (May 20, 1969). _ ! ' ' _ _ ' •

(As revised by errata sheet da ted July 15, IN) _"1"_

" Rules =ha ReguhtlonS .. _ ..... ; _ _! _'.. \ , _, ,, , / _:

§50-204.10 O_upat_onal _g cor_ser_'atioaprogram shall be = ___ _' ___'_ ,_,_"_ ' / /_

exl_suee administered.

(=)P_ote_tio_a_t thee_ec_ Z_s._eo_pol_ive,=_ .. _ _ --- " ' --- :÷_ " /-- ! !of noiseexposure shall be provided noise should not exceed 140 c_ -_

"when the sound levels exceed peaksound pressure _=veL _ !_o iose sho_a in Table 1 of this see- -- -

at ,_owresponse. When noise levels D_a_on _'_ !0o7-are determined by oetxve baud day, hou_ slow res',pom_ _ -i

aaatysis, the equi_Ient A-weighted 8 .................... :. 90 - _ _ "--__.._ / _

sound level may be determined as 6 92 - _ ._.__,_' _m_v_o_._ __ !ollows: (see graph) 4 ......:.................................-... _.('b)When employ_ ace sub- S ...:..............................:..___=._W/ _c_" _4 $ou_o:L_VCL!

_--tedo soundlevelsxceeding"2. " 100 <those l_ted in Table l of t1_i_see_ 11"/ ... ............................... 102 "_ _:_ .I ' '................................._os _ :_ fo_..... .4o""Go- -L-_ '_'.-_''_= - "tion, feasible administrative or en- ,_ ............................... 110 __

gineeringcontrolshalle util£zed-, or'l_ss ..............................i15 _ _AND C_N_R FREqUEnCY 1,_Cye.'_'S=.__-C_DIf such coni_'olsail to reduce ........... "r............. -_:_:,-_ ........ __'____,,_..._-a_=-,__._,_.;

sound Ievds _Sthin the levels of WChen the daily noL_ exposure k

composed Of twO or more I:_rio_s O_ F_ure _ -- Eq.tit'aJcnt SoNnd [Ct'C[ conto_.irs. Octavethe table, personal protective no_se exposure of different levels,equipment shall be provided and t2aexrombm_ed_eet sho,Jd be c_- band sound l_rcs_urc lct'cL_" m_Cf be co,n_c_cCt to the

used to reduce sound levels within s idereal, rather thra the individual ccuicah'_t A-wciTJdcJ .so,_nd lct'cl by p_oHine them onlevels of the table, effectof each. If the sumof the fob '

(c) If the variationsn noise lowi_gfmc_on:C1/T1 + C2/I'2 ... _/_:.,_Zrel,,_/_and nr;tir/_ the A-wcd_htcd sound [et-__'l c_r-level involve maxima at int_rvah Cn/Tn excee&ur_. then the mixed rc,1)onc[it;" to the poin_ of hichc,J pencfrution into 'J_e

of 1 second or less, it is to be con- exposureshouldbe consideredto ex- ;otelld Z,_,ce!c'otttours. This cqmcc:Zent A-_cei_'hted soundeed thelimitalue.Cninddcateshe _ *

'sidereal continuous, t_tal time of e_-aosureat a ._>ec_ed /C_'C/, which may di_cr from the a_ual A-tcci_h:,-_ 4,.D) In all ca._s where the sound no_e _eve[. aud Tn _ndicat_s the total ,_tqnld b'vel o] the noise, is used to determine erposure

levels exceed the values shown thane of exposure permitt_--d at that

herein,a continuing,effecl_vehear- level limits from Table l.

Figure 15

-I0-



REVIEW OF CHABA DOCUMENT PRESENTING DAMAGE RISK CONTOURS

In March 1966, The Journal of the Acoustical Society of America published an

article by the NAS-NRC CHABA Working Group 46 entitled, "Hazardous Exposure to Intermit-

tent and Steady State Noise." (9) This article sets the basis for the derivation of the

DRC which was used in the Walsh-Healy Act on noise exposure as published in the Federal

Reqister, (7) and as subsequently used in the Williams-Steiger Occupational Safety and

Health Act (OSHA) of 1970 (8).

Damage Risk Criteria is presented in this report in the form of statisti.cal linesas shown in the following table (9) :

Estimated percentage of people having various degrees

of presumed NIPTS following ten years of exposure to

a given industrial environment.

Percent ile

50 20 I0

KHZ Median NIPTS in dB

1 I0 20 30

2 15 30 45

3 20 40 60

Figure 16 is a plot of Figure 2, reference 9 and shows the permissible octave band

sound pressure level DRC's for one exposure/day. The permissible hours of exposure,

together with the calculated value of each DRC in units of dBA, are presented. Attention

should be noted to this figure as the modifications applied to this graph form the basis

of the "Equivalent Sound Pressure Contours" graphically used for OSHA noise criteria (8).

Figure 17 is a plot of Figure 3, reference 9, and shows the permissible pure tone

exposure damage risk contours for one exposure/day. The duration in hours,together with

the calculated value of each DRC in units of dBA,are presented. The most striking

difference between Figure 16 (octave band) and Figure 17 (pure tone) is the flattening

of the slope from 125 HZ to 500 HZ and the lower noise exposure levels permissible for

pure tone exposure.

Reference (9) details the basis on which specifications of tolerable exposure to

sound are based. Three postulates are derived specifically concerning Temporary Thres-

hold Shift (TTS) and Permanent Threshold Shift (PTS) and their relationship to each

other

-II-



Fibre 16



Fof America,, Volume 39? NO_ 3,

_i_ze I?

-12-



RELATING THE dB A CONTOUR TO THE CHABA DAMAGE RISK CONTOURS

In March 1967 Botsford published a study (i0, Ii, 12 and 13) relating the findings

of DRC from the CHABA report (9) to a dB x weighting scale.

Although four reports authored by Botsford are referenced, each presents the same

subject in a slightly formated form. The most complete discussion of the subject appearsto be found in reference i0.

As was shown earlier in this paper, the historical development of a set of contour

lines is followed by the historical selection of a dB x contour to represent these lines.

To quote Botsford, "They need simpler methods than those presently available to

facilitate the effective preventative action of which they are capable. In an effort

to meet this need, a simple method of appraising noise hazard has been developed."

In 1953 a noise survey of 40 manufacutirng plants representing 12 manufacturing

industries (14) was published. A total of 580 full octave band measurements were pre-sented.

Botsford chose to relate these octave band measurements to the dB C and dBA scale

as the selected dB x subscript method. Further, the distribution of these noise

measurements in dB A were then related to the nine CHABA full octave band DRC's (Figure 2

of 9).

The study showed "that grouping noises with dB A selected as equivalents to the

contours proposed by CHABA would place most manufacturing noises in the same or highergroup than would a simple full octave band contour plot and would rarely fail to

identify potentially harmful noises," (i0)

Botsford (i0) presents his results as eight contour lines. Further, he states that

this equivalent A weighting sound level which may differ from the actual A weighting

sound level of the noise is used to determine exposure limits from Table I (Figure 15).

COMPARISON OF FEDERAL DAMAGE RISK CONTOURS TO HB A CONTOURS

The Occupational Safety and Health Act (OSHA) presently uses the standards for

Occupational Noise Exposure as presented in the Walsh-HealeyAct (7). Details of the

rules and regulations are provided on Figure 15 of this paper. As the provisions read,

two options are provided for DRC's; namely, the use of dBA contour at nine numerical

levels of exposure/day o_!ra graph of equivalent sound pressure contours if noise levels

are determined by full octave band analysis. The numerical dB A values an--dthe graph of

equivalent sound pressure contours appear to be the same as found in Botsford (12).

Figure 18 is a plot of the graph of equivalent sound pressure contours and Figure

19 is a plot graphically of six of nine of the numerical values of dBA/hOurs of

exposure/day. Figures 20 and 21 are comparison plots of 90 dB A versus 95 dB (equiva-

lent sound pressure contour) and the 95 dBA versus 95 dB (equivalent sound pressure

contour) respectively. A study of these graphs shows a spread of 5 dB for the 90 dB

comparison and i0 dB to 5 dB for the 95 dB comparison. Figure 22 presents a comparison

of the levels in dB A from the table compared to the calculated value in dB A from the

graph of equivalent sound pressure level. The differences in _ dBA range from 6 dB A to

18 dBA (Table I versus the graphical equivalent sound pressure contours).

A study of the four graphs and the table indicates that the equivalent contour

graph is highly sloped below 1 KHZ and beyond 4 KHZ as compared to the dBA contour. This

difference in contour shape contributes significantly to the large Zi dBA calculations

as shown in the table of Figure 22.

Reference 15 noted similar differences as early as April 1970. Private correspon-

dence with Jone (16), U.S Department of Health, Education & Welfare, concerning the

differences noted especially for contour comparisons below 1 KHZ indicated acute aware-

ness of this situation. In the case of a noise which would follow the graphical equiva-

lent sound pressure contours, an excessive level of dB A would be permitted by comparison.

The letter stated that as a result, the Department of Labor is not currently using the

nomogragh (graphical equivalent sound pressure contours) in their enforcement of OSHA

noise DRC's. Table I values of dB A are used only for determining DRC's.

In summary, the current occupational noise standards are based on the dB x method.

The scale of dB A has been chosen to establish DRC's.

-13-



..... l .... z O_.l .... _ ; 1.0 i- - - -"---L-'



Figure 19



.; ! ........ t- !_ -- _:_-_ ...... _---T-_---_;--..... : L---TT-_--_--- ._-_'[T._ _ . "Occupation Noise Exposure", Para. 50-204.10,_

,.q " .-_ ' "!- "" : . ' . " ." [Table I# Federal Register, Vol. 36, No. 96, ._

"Jtto -----------_ ....... -._ , -_,,y2o,1969......

_1.^^- '\_: 1-!- _---_-_d-t---'-!--i _--,-='--= I_'-"l----_--_Tm;-=':l-ll-!-_i Fi6_tTe 20

,,_ \: ....... : - .--i-- ' -'H -- --,----4-- =---_- :-k _ - -r- ","'T__---:_-!---q_,'-i-..-_ " :2T.-b .:'_

_1 ..... ", --_ ...... k-._-+_----_-4---:24-....... !-t-i ,--w---_:-i--:--_---:-__:1__

.-., .-- _, : , 1..... _--,--_--- ,--. t- .......... '_................ .I-;, ......

• i, '. -.t___ '"k_ ___-;-4-' ; " " --------T_

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_._ ' :,_ ..... : -- " .... :............. _D_-_I_

_. . . '-'.-I,-.____." 2 _FERENCE: "Occupation Noise Exposure', Para. 50-204.10,_

l _ . Table I, Federal Register, Vol. 36, Ho. 160

•_t ._ t \ ____, 20,1969..... - Figure 21

- - - . - - - "_-_4 ....... -- • :-', ................ : '-_ t

'_U-i : -F:_" --_ ............... ___--- .-_r ..... ;-:--__ _,_-_. -,...____ .._ ._,._

.... __.______________.... ,_ ,- _ ; _ _ ______,_ -....



COMPARIS_ OF G_ICAL A_ TABULAR DATA FROM

"_C_ATION NOISE EXP_U_", PA_. 50-204.10,

_DE_L _GISTER, VOL. 26, NO. 96, mY 20, 1969

_e following table comp .... the vain,ind_Abet.... Fi6ure 22_e g

ra_ica

ldata and the

_alues

stated inTable I of theabove noted reference.

d_

1 ValueFrom /_ITableI Cu_e _er or (Under)

90 96.0 6.0

95 105.0 10.0

100 113.5 13.5

105 122.5 17.5

ii0 128.0 18.0

115 132_5 17.5

120 135.0 15.0

125 136.0 11.0

- l S -



QUESTION ON THE RELATIONSHIP OF TTS TO PTS FOR CHABA CONTOURS

Since publication of the CHABA DRC's an investigation has been underway to establish

firmly the relationship of TTS to PTS. The CHABA DRC's were used to derive the initial

Federal Occupational Noise Exposure Criteria. The CHABA DRC's are not in use; instead

the more conservative dBA contour has been selected. Nevertheless, the dBA contour is

historically related to the CHABA DRC's as an alternate dB x method.

A master's thesis by Martin (17) is one study in this field. The thesis reports

to show that TTS is not equal to PTS for exposures of impulsive versus white noise

exposure.

A study of the cochleogram by Lipscomb (18) from exposure to rock music by a

guinea pig showed extensive damage from 1 KHZ to 3KHZ and moderate damage from 4 KHZ

to 8 KI_Z. Spectra of noise exposure for the total of 88 hours over 57 days is pre-

sented in the table which follows:

HZ 125 250 500 1K 2K 4K 8K

Full Octave SPL 120 120 120 108 105 i00 90

One observation drawn is that higher levels of low frequency noise (120 dB versusI00 dB) cause more cochlear tissue damage at the mid-frequencies (1 KHZ to 3 KHZ).

Also, that this exposure caused cochlear tissue damage throughout the entire cochlea.

This spectra is similar to the CHABA and to the OSHA graph of equivalent sound pressure

DRC's.

QUESTION OF USAGE OF 20-YEAR OLD NOISE SPECTRA FOR DAMAGE RISK CONTOURS

Botsford (I0) references a 1953 data bank of full octave band noise spectra (14)

to derive a set of numerical distributions for the dBA contour. This data bank made

use of 580 full octave spectra from 40 manufacturing plants representing 12 manufactur-

ing industries. Additional spectra (I0) were used by Botsford from 123 noises from

diesel-powered trucks, tractors, etc., for the dB c - dB A analysis portion of reference

paper (14).

OSHA noise exposure DRC's were extended April 30, 1971, to some 57 million wage

earners in 4.1 million establishments. This represents a significant increase for

defining representative noise exposure spectra from the original 1953 data bank.

Assuming that the original data bank of noise spectra is accurate, it is neverthe-

less not representative of specialized types of industries which matured from 1953 to

1972. The aerospace industry, which today employs about one million workers, had

developed during this period. The type of noise spectra encountered in this industry

needs to be documented in order to relate them to DRC's. Another example is the com-

puter industry which began in the mid-60's and has matured to encompass today's

cybernated factories.

To restate the General Electric advertisement; GE's major product lines continue

to be made up of products of manufacture that did not exist ten years ago.

There is a question, namely, that the statistical data bank of noise spectra is

inadequate for a meaningful comparison to a DRC for occupational noise exposure.

-16-



STATEMENT OF NARROW BAND VERSUS OCTAVE BAND SPECTRA

One industry that has grown to sophistication since the late 1950's is electronic

data processing and analysis of spectra.

The industry/military complex pioneered in this endeavor since it was necessary to

avoid and enhance detection for land, sea and air weapons systems. As a consequency,

narrow band analyses of noise spectra was developed. Narrow band filters of i, 5, i0,

20, 50 and i00 HZ took a second look at full octave noise spectra from machinery.

A simple piston pump for example which appears to have a pump shaft rate and a

pump ripple rate (number of pistons x shaft rate) of 3 harmonics of the ripple rate

when viewed from 1/3 octave band analysis becomes 9 harmonics of the ripple rate when

viewed from narrow band analysis (Figure 22 and 23, respectively). These pure tones

are from an accelerometer and appear some 20 dB above the background noise.

The noise levels of a large industrial tractor in production use today throughout

farms west of the Mississippi are enclosed in Figures 25 and 26. The 1/3 octave band

data (Figure 25) is misleading especially when viewed from analysis of narro w band

spectra.

The ring frequency of a case hardened "swashplate" when subjected to a test to

determine its natural frequencies shows over i0 pure tones from 2 KHZ to I0 KHZ from

a narrow band accelerometer data analysis (Figure 27).

The complex pure tones evidenced in the secondary air duct of a JT3D turbofan

engine are shown in Figure 28.

The first and only postulate for this paper follows:

The characteristic noise spectra from machinery is that of a number

of complex pure tones. The exception is an exhausting jet for which

the characteristic spectra is contoured over a frequency range. This

particular contour may be derived from emperical data relating to the

strouhal value (fd/v).

For example, the far field turbofan noise spectra of a commercial turbofan engine

is shown to consist of a hot gas low frequency spectra, combined with a number of

high level pure tones and lower level white noise spectra (Figure 29).

For a tractor, the noise spectra consists primarily of a series of complex pure

tones at the operator's ear level (Figure 26).

The postulate places emphasis on relating the selection of a DRC to the noise

exposure spectra encountered by industrial workers in each type of manufacturing

facility.

-17-



ACCELERATION LEVELS ON PUMP CASING

1800 RPM. 1/3 OCTAVE.

._--._--E_--® .E_..-_Z-b---,'-_'--r--!-_ "_T_--_---q _-'_- - :-7 --÷-: '_t_-i----l--_-t-dl-:t:__l--_-_t;t'_--:-_2:l

_-'_T:_-- ..... _ ----_ .... :L ..................

-_--='- -'_ ..... ;]t1_'-' ' ' ......... _t_.,-{_,"Eli ...... -_ _- - -,-. _--_

_ _,,._,__9_ __,

......"_"'- '_---z 7 , -;_K_- i-_"1-'.h__tl

Figure 23



-i8 -



_ASURED AUDIO OPERATOR _EL V$ t p_PQSED SAE SPECIFICATION FOR OPERATOR¥

• _ ?.20120

:. _ .... -: _ r: : --._:,:,-':,_ _::----'::_-: -]l-ly- '

Figure 25



8O

Figure 26

-19 -



Figure 2?



i --

• . . ._. " " I0_ _ir_ SE_GI 6_ _ : , .... ._---,- - -I ..... .---! i -

I----- ...... ___,_:. -............. ........... _.... , _ '._ -., ........_....i .... i.... I

_---.-- ...... _ .... _ ..... : .... _-;-- :_---_--:_ ,I _;" _I_--: A ,--_.i-._:---_--T-',

__-_-4 I. __i .... -_....... _--i ± ._ .I-- " -I-±-_- _ _- : -:4.

_-..... _-..... _4-_ _:_ ..... ::--- ___.;-_.J: ' i L---_ ...._-7 :-_ _:__;:---___:__-":-!_. i; _:::-.-.- .l_---h_,_-n_=-. :-*.: _ :-* - ;-', _ -_:-::::--_7_-----:--_-2:-,_.a.

F_,ure 28

-20-





OPEN HOUSE ON DAMAGE RISK CONTOURS

In the preface,reference is made to a statement by Bekesy (1) namely, that the

difficulty in deriving a law to explain the functions of a phenomena often neglects

the implied limits within which the law functions.

Such is the case with the dB x method in which a contour is selected as representa-

tive of "human hearing repsonse." The histology of dB subscript, A, B, C, D, E, each

function adequately for "human hearing response" but only optimally for the dB

ordinate range and type frequency exposure for which they have been postulated to

operate. When the dB x method is extended to all conditions of noise exposure, the

original intent of the dBx method may be invalid.

The selection of dB A, dB B and dB C contours were intended to be consistent with a

range of dB levels. Here dB c was selected as representative of the highest contour

appropriate to analyze noise from industrial and community environments typical ofthe 1930's.

While the dBA contour may represent "human hearing response" for annoyance, it

may not be the dB x contour to represent DRC's for statistical hearing loss and for

subsequent laws on occupational noise exposure.

Even the type of spectra exposure is different today than from the 1950's.

A recognition of this factor for aircraft noise saw the derivation of the dBD scalewhich placed emphasis on high intensity complex tone noise exposure from 1 KHZ to!0 KHZ.

This section reviews DRC's from a number of sources to illustrate the gap which

exists in the definition of a statistically valid DRC.

The AAO0 uses three frequency points and a hearing loss in excess of 25 dB

(average) as a zero point. Hearing loss beyond this 25 dB average is expressed in per-

cent hearing loss using an AAOO procedure (19)&(23). An interesting derivative of an AAO0

data table is presented in Figure 30. The curve of non-noise and general population,

together with the curve of the Mabaan Tribe of the Sudan, is included. Here Cohen (20)

presents a term "sociocusis" to derive statistical hearing loss data from non-

occupational noise exposure.

Figure 31 is a comparison of the dB D and the dB A contour using a 1 KHZ intercept

point. Both these curves represent "human hearing response." Which is correct? Or

are they both correct within the limits that the dBx method functions? It is one

condition to contour a dBx method for annoyance and quite another to contour a dB x

method for statistical hearing loss DRC's.

Figure 32 presents a novel approach to DRC's It is the U.S.S.R. DRC. Note that

increased levels of noise exposure are not reintroduced with the U.S.S.R. DRC. The

acoustics of noise attenuation of marketed products make attenuation of frequencies

beyond 2 KHZ comparatively easy as opposed to frequencies below the 500 HZ range.

Figure 33 presents the NC-85 contour DRC as noted in reference 21. It is similar

in shape to the previous contour. Further increased levels of high frequency noise

are not reintroduced beyond 4 KHZ.

Figure 34 presents the 8-hour DRC for dBA and for the pure tone DRC as provided

in the original 1966 CHABA report (9). Beyond 500 HZ the two curves are almost co-

incident; however, they spread apart some 6 dB, a pressure doubling, at 125 HZ.

Figure 35 presents the 1-hour DRC for dBA and for the pure tone DRC as provided

in CHABA (9) There is a dB A difference of 11.5 dB between the two curves. Further,

an average of a 6 dB spread is evidenced between the two curves. Also, less noise

exposure (up to i0 dB) is premitted from 1 KHZ to 6 KHZ.

-22-



A_e of General Po_ulltlo_

Figure 30





, , . . : : + • . , + ........ +-_ ....... _ L +_+. 4+._ ,

i ' '_ " + ........... Reference '3 of-aZmo_e. + +....

_I:+-1Y__:++-:,_-_::++P:::+:-Y::I-C++_+:++::++-+--_+-+-::+_-i_-:+_+-_+-:_,_+ ,?ol - + ' '++:_ .... : 't ................ "N. ..... + : ++-++---+ t'r'-;-_++-l++'+

+_ :-3 .+ +- ' i+- :::: +-++ -+_._:-i--_::--.p-:-% ,+-+.... +... =+-+:-++-_+kL_'_

- , +---+ ..... _+_- ++÷- .__-+ +__+_ .4-_l_..+-t._±+7' : . . ' " : _i + _ " + :--,. +:+ +i+. _ +.... _.+___+.. _+_+--_.____ &.___.+____,

__-_+-----__+u +_++_ ...... +-----_----- + t ; , , I ,, t : _ - t , '+t [, +-,+ ...... : _- P ... .. F_e_Juemp E_+-_+_---+- +-+- -+[-- _+ ._-! +--+-el _,

m ' i _ T [ + + + ' I r i i . , _ I " + - _ [ i -

L L _ ++.++-,+L u ,+,'.LL_._L L i LLLLLLL i L//LE[L.

Figure 32



Ftgure 33



Fibre



Fi_e 35



CONCLUSIONS AND RECOMMENDATIONS

i. The choice of the dB x method needs to be restudied as an acceptable simplified

method for relating DRC's to occupational noise exposure.

2. The dB A contour may be inappropriate for specifying numerical levels of DRC

exposure.

a) The A-contour is appropriate for intensity levels in the range from 48 to

70 dB (Figure 7).

b) The data bank of noise spectra used to derive the selection of the A-contour

is over 20 years old and does not represent the current OSHA condition on

noise spectra exposures.

c) The relationship of TTS and PTS per the three postulates of the CHABA report (9)

remains in question.

3. A data bank of narrow band and 1/3 octave band noise spectra is needed to

statistically relate contours of noise exposure to the DRC's for the 57 million

wage earners working 4.1 million establishments now covered by OSHA.

4. The postulate presented in this paper, namely, that the dominant characteristicof noise spectra from machinery is that of complex pure tones needs to be

investigated using the data bank information from Item 3 above.

a) For the aerospace industry covering one million workers the DRC specifications

may require relating to spectra of noise exposure involving high levels of

cempiex pure tones.

5. The practice of reintroducing higher permissible levels of noise exposure beyond

4 KHZ for DRC's is questioned.

a) Several DRC specifications do not reintroduce higher noise levels beyond

4 KHZ (Figures 13, 14, 32 and 33).

6. Since a large number of sound level meters and electronic processing equipment

is in private and industrial ownership, any retrofit DRC selection will requirethe utilization of "equivalent" dB x tables that are statistically acceptable.

7. The selection of a DRC should require a detailed statement covering the

range of validity within which the DRC applies.

8. A next generation DRC for occupational noise exposure should consider

recommentations made by the World Health Organization (22).

a) One item from this reference states; "That it is unacceptable (and not in

agreement with data from other countries) that it should be considered

normal for 50 percent of the workers reaching age 65 to have a hearing

handicap."

-26-



REFERENCES

Reference

Number

1 Bekesy, G. Yon, "The Missing Fundamental and

Periodicity Detection in Bearing", ASA, Vol. 51,

No. 2, February 1972

2 Stevens, S. S., Hearin_ Its Psychology and

Physiology , John Wiley & Sons, 1938

3 Kryter, K.D., The Effects of Noise on Man

Academic Press 1970

4 Stevens, S. S., "Perceived Levels of Noise by

Mark VII and Decibels (E)", ASA, Vol. 51, NO. 2,

February 1972

5 "Noise Control Safety Orders and Threshold Limit

Values", Division of Industrial Safety, State of

california, Article 55, November 1955

6 "General Safety and Health Standards for Federal

Supply Contracts", Walsh-Healey Public Contract

Act of 1934, United States Department of Labor,

Para. 50-204.293, Washington D. C., 1967

7 "Occupational Noise Exposure", General Safety and

Health Standards for Federal Supply Contracts,

Walsh-Healey Public Contract Act of 1934, Federal

Register, Vol. 34, No. 96, May 20, 1969

8 "Williams-Steiger Occupational Safety and Health

Act of 1970 ", (0SHA), Public Law 91-596,

December 29, 1970

9 Kryter, K. D., "Hazardous Exposure to Intermittent

and Steady State Noise", I_AS-NRC CHABAWorkingGroup 46, ASA, Vol. 39, NO. 3, March 1966

i0 Botsford, J. H., "Simple Method for Identifying

Acceptable Noise Exposures", ASA, Vol. 42, NO. 4,

March 1967

ii Botsford, J. H., "Damage Risk", Transportation

Noises, A Symposium on Acceptability Criteria,

Chalupnik, J. A., Editor, University of

washington Press, 1970

12 Botsford, J° H., "Current Trends in Damage Risk

Criteria", Sound and Vibration, Vol.4, No. 4,

April 1970

13 Botsford, J. H., "Control of Noise Through

Engineering", ASHA, NO. 4, 1969

14 Karplus, H. B. and Bonvalett, G. L., "A Noise

Survey of Manufacturing Industries", American

Industrial Hygiene Association, Quarterly 14,

Pages 235 to 263, 1953

15 Hirschorn, M., "The walsh-Healey and 90 dBA",

National Safety News, April 1970

16 Jones, H. H. Private Correspondence, Acting

Chief Physical Agents Branch, Department of Health,

Education and Welfare, Cincinnati, Ohio,

February 1972

17 Martin, R., "Recovery Slope of Auditory Fatigue

Induced by Gunfire", M_ster's Thesis, Arizona

State Univeristy, Tempe, Arizona, june 1972

iS Lipscomp, D. M., "Noise in the Environment,

Recreational and EnviroD/nental Sounds", MAIC0

Audiological Series VIII, 1970

19 "AA00 Method for Calculating Percent Hearing Loss",

Page 102, Audiolog_)Newby, H. A., Appleton-CenturyCrafts, 1964

20 Cohen, A. et all, "Sociocusis - Bearing Loss from

Non-occupational Noise Exposure", Sound and

Vibration, November 1970

21 Rose, D. E., "Bearing Darm_ge Risk Contour", Table

Table 13.6, Bearing Assessment, Prentice Hall Inc.,

1971

22 Cuadra, E., "World Health Organization's First

Consultation on Noise". Sound and Vibration,

February 1972

Documents

A Review of Damage Risk Contours for Occupational Noise Exposure