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NIST Technical Note 1641

PASS Sound Muffle Tests Using A

Structural Firefighter Protective

Ensemble Method

J. Randall Lawson

Nisr

National Institute of

Standards and Technology

U.S. Department of Commerce

NIST Technical Note 1641

PASS Sound Muffle Tests Using A

Structural Firefighter Protective

Ensemble Method

J. Randall Lawson

Fire Research Division

Building and Fire Research Laboratory

National Institute ofStandards and Technology

Gaithersburg, MD 20899-8661

July 2009

'^^ Homeland

Security

Department of Homeland Security

Janet Napolitano, Secretary

Federal Emergency Management Agency

W. Craig Fugate, Administrator

United States Fire Administration

Glenn Gaines, Assistant Administrator

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Deputy Director
Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Technical Note 1641

Natl. Inst. Stand. Technol. Tech. Note. 1641, 32 pages (July 2009)

CODEN: NSPUE2
CONTENTS

List of Figures ii

List of Tables ii

Abstract 1

LO INTRODUCTION 2

2.0 TEST DESCRIPTION 2

2.1 TEST SPECIMENS 2

2.2 TEST INSTRUMENTATION 3

2.3 TEST ENVIRONMENT 4

2.4 TEST PROCEDURE 5

2.4.1 PASS DEVICE TESTING 5

2.4.2 ORDER OF TESTING 6

2.4.3 DETAILED TEST PROTOCOL 10

3.0 TEST RESULTS AND DISCUSSION 12

4.0 RECOMMENDATIONS FOR FUTURE WORK 22

5.0 CONCLUSIONS 23

6.0 ACKNOWLEDGEMENTS 23
LIST OF FIGURES

Figure 1 Characterization of the dBA decibel scale 3

Figure 2 Photograph showing calibration of sound meter and laser

used for alignment of sound meters and PASS devices 4

Figure 3 Photograph showing room and arrangement for unobstructed

testing of clip-on PASS devices 5

Figure 4 Diagram showing standard arrangement for PASS sound level testing 6

Figure 5 Photograph showing SCBA with integrated PASS on test stand 7

Figure 6 NFPA 1982 position 1 8

Figure 7 NFPA 1982 position 2 8

Figure 8 NFPA 1982 position 3 9

Figure 9 NFPA 1982 position 4 9

Figure 10 NFPA 1982 position 5 10

Figure 1 1 PASS Device A - Change in muffle position sound level vs. unobstructed sound level (0 line) 14

Figure 12 PASS Device B - Change in muffle position sound level vs. unobstructed sound level (0 line) 15

Figure 13 PASS Device C - Change in muffle position sound level vs. unobstructed sound level (0 line) 16

Figure 14 PASS Device D - Change in muffle position sound level vs. unobstructed sound level (0 line) 17

Figure 1 5 PASS Device E - Change in muffle position sound level vs. unobstructed sound level (0 line) 18

Figure 16 Photographs showing background sound level measurement tests 22

LIST OF TABLES

Table 1 Summary of PASS Device Sound Level Variability 19

Table 2 Fire Apparatus and Fire Fighting Equipment Sound Levels 20

Table 3 Background Sound Levels 21

11
PASS Sound Muffle Tests Using A Structural Firefighter

Protective Ensemble Method

By

J. Randall Lawson

Abstract

Firefighters and other emergency responders often work in adverse environments. The

operating environments can be very noisy. Personal Alert Safety Systems (PASS)

devices are safety systems that emit an audible alarm signal when an emergency

responder stops moving. This alarm signal serves as a means for others to rapidly locate a responder who may be injured or incapacitated. The 2007 edition of National Fire

Protection Association, NFPA 1982, Standard on Personal Alert Safety Systems (PASS)

established a means to evaluate the muffling (attenuation) of sound level from a PASS

device worn by an emergency responder who is down on the floor. The standard

prescribes five different test positions that are assumed when measuring sound level

attenuation from a firefighter, fully dressed in their NFPA 1971 fire fighting ensemble,

while wearing a PASS device that is in full alarm. NIST tested five different pass

devices in an open room environment to determine relative signal level attenuation for

each device. These tests demonstrate sound level losses ranging from approximately 9 %

dBA to 19 % dBA. These signal losses are associated with the type of device, direction of

measurement relative to the orientation of the PASS device, and attenuation from the

firefighter's body obstructing the sound path. This report also contains background

sound level measurements with dBA measurements from fire fighting apparatus and

power tools that are commonly used on the fireground.

KEY WORDS: Alarms; emergency responder; firefighter; muffle; PASS; safety; sound

attenuation; sound level; standards
1.0 INTRODUCTION

Personal Alert Safety Systems (PASS) devices have been used by the fire service since or before the early 1980's for locating and rescuing downed firefighters. The National Fire

Protection Association (NFPA) published the first standard for PASS devices, in 1982[1].

These devices electronically sense motion and the lack of motion from a person wearing

the device. When the device senses that there has not been any motion, after a prescribed

period of time, the device goes into alarm by emitting an audible signal. These devices

generally have lights that also flash when the alarm is activated. The combination of the

audible alarm and flashing lights are designed to assist other emergency responders in

locating a potentially injured firefighter. PASS devices are also available with a radio

transmitter that sends the alarm to a command post when it is activated. With all of these

PASS devices the emergency alarm can also be activated manually by the user.

The objective of this study was to better understand the relative change in sound level

from an activated PASS when it is being used by a firefighter. The alarm signal sound

level can be affected by a range of factors including location of PASS device on the

firefighter (front, side, or rear), position of the firefighter (prone, supine, fetal), the

volume of the room, the wall linings or materials, the presence of furniture or other

objects, and background sounds. NFPA PASS Standard 1982 (2007) includes a muffle

test where sound attenuation is measured in a sound chamber. While this allows each

PASS device to be evaluated under carefully controlled conditions, the testing protocol

includes only the location of the pass and the position of the firefighter. This study

examined the attenuation of the alarm signal in a more typical room environment than a sound chamber. This study also documented typical background sound levels for fire apparatus, fire fighting equipment, offices, living room, and vehicles. Comparing the

background sound levels with the sound attenuation data provides a better understanding

as to whether the decreased sound levels will be distinguishable above background

sounds. Figure 1 provides a comparison of various sound levels on the standard dBA

decibel scale [2, 3]

2.0 TEST DESCRIPTION

2.1 TEST SPECIMENS

Five different PASS devices meeting the requirements of the 1998 edition of NFPA 1982 were evaluated in this study [4]. Two PASS devices were clip-on designs and three were

integrated into the construction of Self-Contained Breathing Apparatus (SCBA) systems.

The PASS designs that were clip-on are stand alone units that do not depend on the

operation of the SCBA or other firefighter equipment. The clip-on devices are normally

attached by a clip to the front of a firefighter's SCBA harness. One of the integrated
PASS systems had the alarm signal device located on the back of the SCBA pack, and all 130 dBA

95 dBA Jet Aircraft

NFPA1982 Pain

PASS alarm Threshold

OdBA 40 dBA

Hearing Small

Threshold Theater

80 dBA 120 dBA

Hearing Loss Rock Band

Threshold Concert

Long Exposure

Figure 1. Characterization of the dBA decibel scale.

other integrated PASS alarm signal emitters were located on the front straps of the

harness. At the time of testing, all five PASS device designs were typical of devices used

by emergency responders. Four of the devices were new, and one clip-on device had

been previously used in nondestructive testing, at NIST.

The two clip-on PASS devices were activated by manually removing a key from the

device. The three integrated PASS device systems were connected into the SCBA air

management system and were activated by SCBA operation. All five devices were

battery powered, and they all had a switch that could be manually operated for activating

the alarm signal.

2.2 TEST INSTRUMENTATION

The sound level meters used during this study were EXTECH Model 407764 data

logging meters with the capability of storing up to 16,000 readings.* These meters

recorded the sound level and a timestamp. Each handheld meter udlized a RS-232 port to download logged data. Each of the sound level meters was initially calibrated by the

manufacturer using a NIST traceable sound level standard. Additionally, before each

PASS device test, the sound level meters was rechecked using a portable sound level

calibrator. This battery operated NIST traceable sound level calibrator provides

calibradon output signals at either 94 dBA ±0.5 dBA or 1 14 dBA ±0.8 dBA. Since the

primary decibel level for PASS output is 95 dBA, all sound level calibration checks were

carried out at the 94 dBA level setting (Figure 2).

*Certain commercial entities, equipment, instruments, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the

procedure and practices used. Such identification is not intended to imply recommendation,

endorsement, or implication that the entities, products, materials, or equipment are necessarily the

best available for the purpose. Nor does such identification imply a finding or fault or negligence

by the National Institute of Standards and Technology.
Figure 2. Photograph showing calibration of sound meter and laser used for

alignment of sound meters and PASS devices.

2.2.1 Measurement Uncertainty

The manufacturer's published accuracy for the sound level meters over a range of

30 dBA to 130 dBA is ±1.5 dBA with a resolution of 0.1 dBA. Although the

specifications for the sound level meters and the calibration standard are relatively tight,

it is estimated that the combined standard uncertainty (i.e., estimated standard deviation)

Wc for these sound level measurements is on the order of ±6 dBA and a coverage factor

k = l. Since it can be assumed that the possible estimated values of the standard are approximately normally distributed with an approximate standard deviation Wc, the

unknown value of the standard is believed to lie in the interval defined hy U = k Uc with a

level of confidence of approximately 95 %.

2.3 TEST ENVIRONMENT

2.3.1 TEST ROOM

The test room used for this study was similar to a space that would be found in an office

building or a light industrial building. The average background sound level measured in

this test room was (42 ±2) dBA which is similar to that found in a typical office

environment. The test room used in this study measured 4.1 m (13 ft 6 in) high, 4.8 m

(16 ft) wide, and 6.5 m (21 ft 6 in) long. The room was clear of any obstructions,

including fiimiture and columns. The upper parts of the walls were covered with

50.8 mm (2 in) thick, fabric covered, low density, glass fiber batting. The lower part of

the walls was covered with painted steel panels and some wall surfaces extended into the

room to provide surfaces for utility outlets. The room had a concrete ceiling with a textured spray paint finish, and the concrete floor was covered with vinyl flooring tile. See photograph of the room test area in Figure 3. The ceiling and the walls also had
exposed air-conditioning ducts and outlets. The room's temperature and humidity were

controlled by the building's air-conditioning system. Room temperature was nominally

(21 ± 2) °C (70 ± 4) °F and the relative humidity was typically (50 ± 2) %. Temperature

and humidity conditions are provided since these environmental conditions may have an

affect sound propagation.

Figure 3. Photograph showing room and arrangement for unobstructed testing of

stand alone PASS devices.

2.3.2 BACKGROUND SOUND LEVEL MEASUREMENTS

The background sound level measurements were made inside buildings or vehicles to obtain typical background sound levels that may be found inside residential and

commercial office buildings or inside a fire department officer's vehicle. The fireground

fire apparatus and equipment sound level measurements were all made outside.

2.4 TEST PROCEDURE

2.4.1 PASS DEVICE TESTING

The test procedure was similar to the muffle test as described by the NFPA 1 982

Standard on Personal Alert Safety Systems (PASS), 2007 edition [1]. For condidoning

purposes, all PASS devices were maintained in a nominal (21 ±2) °C (70 ± 4) °F and

50 ±2 % relative humidity environment for a period greater than 30 days prior to being

tested. The basic test layout from the NFPA standard is shown in Figure 4. As noted
above in section 2.3, the room obtained for these tests was not wide enough to allow for

all four measurements (0°, 90°, 180° and 270°) to be made without repositioning. As a

result, one set of sound measurements was made to obtain data for the 0° and 1 80 °

positions (t) of the PASS device. (Figure 4) Then the PASS device was turned 90°

counterclockwise (<—) so that sound instruments could measure the second set of data and

obtained readings for the 270° and 90° locations. (Figure 4)

Note: 3 m distance

from PASS to all sound meters.

Figure 4 Diagram showing standard arrangement for PASS sound level testing.

Before any sound level tests were conducted, new batteries were placed in each PASS

device, and the device was briefly activated to insure that it was operating properly.

Additionally, all sound meters were operated with fully charged batteries.

2.4.2 ORDER OF TESTING

The following describes the testing order used for measuring sound muffling for each of

the five PASS devices: Photographs showing each of the test positions are located in

Figures 6 through 10. In the photographs, the direction of the firefighter's head is always

pointing toward the 0° measurement location.

1 . Each device was tested when suspended from a support so that no obstructions

existed between the device and the sound level meters. This was done to measure maximum baseline sound level output for each PASS for comparison with results

fi-om the muffled tests. (Figures 5 through 10)
2. Position 1 : Face down with arms fully extended out to the sides. (Figure 6)

3. Position 2: Supine left as far as possible, arms down along sides (Figure 7)

4. Position 3: Supine right as far as possible, arms down along sides. (Figure 8)

5. Position 4: Fetal, knees drawn to chest as far as possible, arms around legs, and

lying on right side. (Figure 9)

6. Position 5: Fetal, knees drawn to chest as far as possible, arms around legs, and

lying on left side. (Figure 10)

Note that in positions 4 and 5 that fire fighters could not wrap their arms around their legs

in a fetal position. (Figures 9 and 1 0)

Figure 5. Photograph showing SCBA with integrated PASS on test stand.
Figure 6. Position 1: Face down.

Figure 7. Position 2: Supine Left.
Figure 8. Position 3: Supine right.

Figure 9. Position 4: Fetal right.
Figure 10. Position 5: Fetal left.

2.4.3 DETAILED TEST PROTOCOL

The following protocol was used with all of the PASS tests.

2.4.3. L Instrumentation Layout

The center of the test floor was marked by placing a black tape X on the point of

symmetry. Then two other points were measured 3 m (9.9 ft.) in opposite directions from

the center and marked on the floor. This became the 0° sound measurement point and the

180" sound measurement point. By rotating the PASS device 90° these sound

measurement points also became the 90° sound measurement point and the 270° sound

measurement points. Each of these three points was also marked with an indelible

marking pen. Alignment of the three points was accomplished by using a laser beam

across the floor.

Before each set of tests, each of the sound meters was calibrated. The sound meters were

then attached to camera tripods and were positioned to align the meter's microphone

directly above the previously described measurement locations. At this point in the test, the sound meters were operating but were not recording data. The height of the sound

10
meters above the floor was set at 0.6 m (2 ft.). This was chosen to approximate the head

height of a crawling firefighter.

2.4.3.2 Supports for Unobstructed Tests

The unobstructed tests were conducted by suspending PASS devices over the point of

symmetry from vertical supports. The stand alone devices were suspended from a laboratory stand, and the integrated devices were suspended from an aluminum frame

that allowed for the SCBAs to be suspended by the shoulder straps. (Figures 3 and 5)

2.4.3.3 Firefighter Ensemble Tests

When sound muffling tests were conducted using the firefighter ensemble, the sound

producing part of the PASS device was located over the symmetry point on the floor. In these tests, the firefighter wore their normal structural fire fighting ensemble that meets

NFPA 1971 Standard on Protective Ensembles for Structural Fire Fighting and Proximity

Fire Fighfing [1]. (Figures 6 through 10)

2.4.3.4 Conducting the Test

After all elements for a test were in place and operating, each sound level meter was set to begin logging, and then the PASS device was manually acdvated. The PASS device

remained in a full alarm mode for a period of approximately two minutes while the

instruments collected sound level data. At the end of the two minute period the PASS

device was silenced and data logging was stopped. The PASS device was then turned

90°, and the procedure was repeated. All test personnel wore hearing protection during

the periods of alarm activation.

2.4.3.5 Managing the Sound Level Data

When the set of two tests were completed (which allowed for taking measurements at the

0°, 90°, 180°, and 270° points) the sound meters were attached to a portable computer and

each data file was downloaded, saved, and archived. The data were then plotted,

analyzed, and are presented in Section 3.

2.4.4 BACKGROUND SOUND LEVEL MEASUREMENTS

Measurements for background sound levels were conducted using similar methodology

as that for the PASS sound measurements discussed above. Two different fire department companies participated in this measurement effort (see acknowledgements),

and it involved more than twenty pieces of fire department equipment that are described

in Tables 2 and 3, of Section 3.2. All of these sound level measurements were made

outside at each of the respective firehouses. The measurements were made on clear days

with the temperature at about 20 °C (68 °F). Sound level measurements were made

concurrently with two calibrated sound meters located 0.6 m (2 ft.) above ground level. One measurement was typically made 3 m (9.9 ft.) from the front of the apparatus or

11
equipment and is designated the 0° measurement. The second measurement was typically

made 3 m (9.9 ft.) from the side of the apparatus or equipment and is designated the 90°

measurement. Additionally, the 90° sound measurements were typically made at locations on the exhaust side of the equipment where the highest sound levels would be

expected. The radio sound measurements were made at 1 m (3.3 ft.) from the radio at both the 0° and 90° locations relative to the speaker/mic position. The dBA values for

each of the background sound level measurements represent an average observed over a 30 second measurement time period. Results are presented in Section 3.2.

Additional sound measurements were also made to quantify some normal sound levels

that may be experienced in residential, office, and building mechanical space settings.

All of these measurements, except measurements on the inside of the vehicle, were made

at a location 0.6 m (2 ft.) above ground level. These measurements were made at only

the 0° location relative to the item of interest and did not include a measurement at a 90°

location. These results are also reported in section 3.2

3.0 TEST RESULTS AND DISCUSSION

3.1 PASS DEVICE RESULTS

Test data for each of the PASS devices are presented in Figures 1 1 through 15. There are four plots for each PASS device. Each of the four plots represents one of the sound

measurement points. The "0" sound level line on each plot represents the reference

sound level output from the unobstructed PASS device. The decibel level bar graph data

plots extending from the "0" line represents the change in sound level relative to the

unobstructed sound level test condition. The bar graph plots show respectively from left to right results from each ensemble muffle position 1, 2, 3, 4, and 5. The PASS device

designation is located on the top of each plot and the figure title. (Figures 1 1 through 15)

Each graphed data value incorporates a reference bar showing the sound test measurement uncertainty of ± 6 dBA.

The objective of these data plots and values reported in the summary table (Table 1) is to provide the reader with a comparison of sound level muffling as it relates to the position

of the PASS device relative to direction of sound travel away from the device. From

these data plots, it is observed that sound levels for all five PASS device systems changed

with ensemble test position. Note that all PASS alarm signal devices were located on the

front harness, except for PASS device D which was located on the back. This alarm

signal device location on the back of the harness produced a more uniform distribution of

sound from the PASS system. In some cases, the sound level did not fall below the

unobstructed test level but increased above this baseline. Each of the PASS devices,

during ensemble testing, exhibited cases where measured sound levels exceeded the

unobstructed test baseline values. This appeared primarily to be a result of the PASS

device alarm orientation relative to the sound meters. In the unobstructed tests the PASS

devices were suspended vertically. In this orientation, some PASS device alarm

components were directed towards the floor. In the ensemble tests the PASS devices

12
typically were laying horizontally, changing the output direction from the alarm and in

some cases possibly providing a more direct signal path to the sound meters.

PASS device B exhibits the greatest decrease in sound level during the ensemble

muffling tests. It shows a sound level amplitude reduction of approximately 1 5 dBA in

the 0°, ensemble position 5 test and approximately 19 dBA decrease in signal amplitude

with the 180°, ensemble position 5 test condition. Figure 12. Conversely, PASS device D

exhibits sound level increases for three of the five 90° ensemble positions. Also, D shows

only slight changes in signal output for the 0° and 180° positions. (Figure 14)

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18
A summary of the data plots is located in Table 1. The objective of this table is to provide the reader with a summary of PASS device results focused on maximum changes

measured for sound levels from each device; additionally, the overall dBA percent

variation is shown. Note that the sound level changed over a range of approximately 9 %

to 19 % for the set of PASS devices tested. This amount of variation is not small when it

is considered that dBA sound level measurements are made on a logarithmic scale.

Therefore, the change in apparent sound level to the human ear could be significant.

Table 1 Summary of PASS Device Sound Level Variability

Note: Per section 2.2.1, measurement uncertainty for all table values is ±6 dBA.

PASS Device Maximum

Difference

(dBA)

Minimum

Difference

(dBA)

Percent

Variation

(averaged over

5 positions)

(% dBA)

A -10 14.1

B -19 19.2

C -11 1 14.0

D +8 13.2

E -6 8.6

An additional observation related to testing, note in Figures 9 and 10 that NFPA 1982

uses the following definitions for the positions: Position 4 Fetal, knees drawn to chest as

far as possible, arms around legs, and lying on right side. Position 5 Fetal, knees drawn

to chest as far as possible, arms around legs, and lying on left side.

As clearly observed in Figure 10, the test subject could not pull the legs up high enough

to achieve the prescribed position. It was found that the firefighting ensembles restricted

body movement preventing the firefighter from bringing the legs up high enough to wrap

the arms around their legs.

3.2 BACKGROUND SOUND LEVEL RESULTS

Table 2 provides information on background sound levels that may be experienced on the

fireground. The primary focus of this table is to provide data on sound levels produced

by fire department apparatus and fire fighting equipment. It should be noted that results

in this table represent sound measurements for single pieces of equipment. The results do

not account for sound levels that may actually be found on the fireground when multiple

fire apparatus and multiple pieces of fire fighting equipment are operating at the same

time. The sound levels reported in Table 2 represent the mean value from sound level

sampling during a time period of approximately 30 seconds. Each of these reported

values has a measurement uncertainty of about ± 6 dBA. The first row of data provides

background sound levels measured at each of the two test sites. Generally, these ambient

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background sound levels were not directionality different and only single values are reported for these cases. The first column provides a description of the equipment being

tested. The second column identifies the distance between the measurement instruments

and the test item. The third and fourth columns provide 0° and 90° dBA values measured

with Company 1 2 equipment and the fifth and sixth columns provide 0° and 90° dBA

values measured with Company 53 equipment. Column seven provides comments

designed to assist the reader with understanding conditions for each of the measurements.

Table 2

Fire Apparatus and Fire Fighting Equipment Sound Levels

Note: Per section 2.2.1, measurement uncertainty for all table values is ±6 dBA.

Description Distance Company 12 Company 53 Comments

(m)

0°

(dBA)

90°

(dBA)

0°

(dBA)

90°

(dBA)

Test Site n/a 62 62 54 54

Ambient

sound level.

Fire Engine 3 80 79 77 76

Engine at Idle

3 87 85 81 80 Engine high

Idle

Siren 3 109 100 109 104

Federal Q,

Electronic

3 110 108 108 109

Air Horn 3 109 107 109 106

Apparatus

Backup

Alarm

3 81 83 90 87

Operating

Pump 3 85 85 79 80 Idle

3 97 95 88 91 MaxRPM

PPV Fan,

Gas Engine

3 106 97 97 92

Chain Saw

3

81 80 75 71 Idle

100 96 106 102 MaxRPM

Circular,

Cutoff Saw 3 81 79 75 71 Idle

3 105 103 106 102 MaxRPM

Portable

Radio, High

Volume

1 79 76 83 75

Without

Apparatus

running

1 87 85 85 82

With

Apparatus

miming

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Table 3 provides 30 second average sound level measurement values for a variety of

residential, office, vehicle, and mechanical room locations. The table provides

information on the location or type of equipment being examined, distance from the

equipment, the measure sound level in dBA, and comments describing the measurement.

Additionally, smoke detector and commercial fire alarm dBA values are provided for

comparison. These data are based on the NFPA 72 standard [5] for sound levels for

residential smoke alarms and commercial fire alarms.

Table 3

Background Sound Levels

Note: Per section 2.2.1, measurement uncertainty for all table values is ±6 dBA.

Location and

Equipment

Distance

(m) (dBA) Comments

Two Person

Office n/a 43

Measurement center of office space (3.3 m

Wx4.8mLx3.3mH)

Ringing Office

Telephone 2 65 Same office describe above.

Home Living Room

n/a 36

Measurement made in center of room,

doors and windows closed

Suburban-Outdoors

Neighborhood n/a 48

Midday ambient sound level, low traffic

volume

Residential Smoke

Detector

See

comment 85

Ref at 10 ft. distance.

NFPA 72, National Fire Alarm Code

Commercial Fire

Alarm System

See

comment 110

Max. at minimum distance,

NFPA 72, National Fire Alarm Code

Inside SUV Vehicle n/a 36

Center top dash level measurements,

windows & doors closed, engine off

n/a 47 Windows & doors closed, engine running

n/a 60 Windows closed, driving 35 mph

Office Building

Mechanical Space n/a 70

Average of sound levels measured in an open floor plan mechanical space

Building AC Vent

Fan 3 68

Vent fan operating at 850 RPM

Building AC Vent

Fan 3 85

Vent fan operating at 850 RPM and guard

housing was vibrating

Industrial

Combustion Fan 3 80 Combustion fan operating at 1525 RPM

Computer Room

n/a 64

Room with 43 operating desktop sized

computers. Center of room measurement.

Room size (3.3 m W x 7.3 m L x 3.3 m H)

Fan-Smoke Ejector

3 92

Electric variable speed fan on max. setting

2200 RPM

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The dBA values measured in this report do not fully account for all of the sound that may

be experienced on a fireground, but is a sample of sounds that may be experienced. It also does not account for the level of sound lost by fire fighters who are properly wearing

their personal protective equipment (PPE), i.e. helmets; ear flaps, hoods, and coat collars can reduce the amount of sound that a working fire fighter may hear. Results from these

measurements of background and fire equipment sound levels demonstrate that the

95 dBA sound level from a PASS device alarm has the potential for being lost within the

normal sounds generated while responders are operating on the fireground.

Figure 16. Photographs showing background sound level measurement tests.

4.0 RECOMMENDATIONS FOR FUTURE WORK

Sound data collected during this study demonstrates that sound levels can be muffled by

changes in firefighter positions or the orientation of the alarming PASS device.

Additionally, potential sound levels associated with fireground operations may be loud

enough to challenge PASS device alarm sound performance. Additional research areas which could provide better characterization of the attenuation of PASS alarm signals

include:

• Measure the sound attenuation (muffling) associated with blockage by

furnishings and building contents.

• Measure the muffling associated with a range of different types of construction,

walls and floor ceiling systems.

• Measure sound levels with multiple pieces of fire apparatus and fire fighting

equipment running.

• Measure sound level attenuation caused by the proper use of PPE.

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5.0 CONCLUSIONS

Data from this limited study demonstrate that PASS alarm sound levels can be muffled

by personnel wearing typical firefighting ensembles when oriented in the test positions

specified in NFPA 1982. Additionally, the data demonstrates that PASS alarm sound

levels may be reduced by simply changing the unobstructed orientation of the PASS

device. The findings suggest that the loss in PASS device amplitude due to orientation

and muffling has the potential for reducing sound levels to a point that may make it more

difficult for rescue personnel to locate an incapacitated firefighter.

Sound measurements presented in this report for PASS muffling and ambient

background, fire fighting apparatus, and fire fighting equipment show that the 95 dBA

PASS device alarm level may be seriously challenged by other sounds exposures on the

fireground. The impact of muffling of the alarm signal and background sounds should be

incorporated into performance metrics for PASS devices to insure the alarm signal are adequate to locate incapacitated fire fighters

6.0 ACKNOWLEDGEMENTS

Appreciation is extended to members of. Company 53, the NIST Fire Protection Group:

Chief Thomas Rhodes, Chief Danny Baker, Capt. Mark Miller, Lt. Ivan Todd, and

FF/EMT Eric Inkrote for their assistance in conducting this study. Appreciation is also to extended members of, Company 12, the College Park Volunteer Fire Department, Prince

George's County, MD, particularly Deputy Chief Stephen Kerber and Firefighter

Matthew Machala for their assistance in collecting apparatus sound data for this report.

The support of U.S. Fire Administration, especially project officer Brad Pabody is greatly appreciated.

7.0 REFERENCES

1. National Fire Protection Association, NFPA 1982 Standard on Personal Alert Safety

Systems (PASS), 1982 Edition, Quincy, MA.

2. Federal Interagency Committee on Aviation Noise, "How do we Describe Aircraft

Noise?" www.fican.org.

3. U.S. Department of Health and Human Services, "Criteria for a Recommended

Standard, Occupational Noise Exposure, Revised Criteria 1998," Centers for Disease

Control and Prevention, Ohio, 1998.

4. National Fire Protection Association, NFPA 1982 Standard on Personal Alert Safety

Systems (PASS), 2007 Edition, Quincy, MA.

5. National Fire Protection Association, NFPA 72, National Fire Alarm Code, 2007

Edition, Quincy, MA.

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