NBSIR 76-1016

Mobile Home Smoke Detector

Siting Study

William M. Gawin and Richard G. Bright

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1976

Final Report

U S. DEPARTMENT OF COMMEIICE

NATIONAL BUREAU OF STANOAROS

NBSIR 76-1016

MOBILE HOME SMOKE DETECTOR

SITING STUDY

William M. Gawin and Richard G. Bright

Center for Fire Research

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1976

Final Report

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, S^emary

James A. Baker. Ill, Under Secntary

Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES v

Abstract 1

1. INTRODUCTION 1

2. DESCRIPTION OF TEST SETUP 3

2.1. Test Enclosure 3

2.2. Smoke Detectors 3

2.2.1. Smoke Detector Type 3

2.2.2. Smoke Detector Sensitivity 4

2.2.3. Smoke Detector Locations 5

3. TEST PROCEDURES 6

3.1. Test Fires , 6

3.1.1. Smoldering Fires 6

3.1.2. Flaming Fires 6

3.1.3. Fire Location 7

3.1.4. Weather Condition 7

3.2. Test Series 7

3.2.1. Series A , 7

3.2.2. Series B 9

3.2.3. Series C 9

3.2.4. Series D 9

4. DISCUSSION OF TEST RESULTS 10

4.1. Test Series A 10

4.2. Test Series B 11

4.3. Test Series C. . 12

4.4. Test Series D. , . 14

4.5. Weather Conditions » . . . . . . . 16

5. CONCLUSIONS 16

6. REFERENCES 18

iii
LIST OF FIGURES

Page

Figure 1. Return Air Vent in Heater Compartment. . . 19

Figure 2. Exterior of Mobile Home (Living Room End) . 20

Figure 3. Photoelectric Smoke Detector Chamber ... 21

Figure 4. Smoke Detector Test Chamber 22

Figure 5. Wood Crib 23

Figure 6. Radiant Furnace 24

Figure 7. Wood Crib Test Setup . 25

Figure 8. Smoldering Wood Crib Fire Test ...... 26

Figure 9. Detector Locations — Test Series A. . . . 27

Figure 10. Detector Response Time vs Sensitivity —

Test Series A, Tests 1 and 2 28

Figure 11. Detector Response Time vs Sensitivity —

Test Series A, Tests 3, 4 and 5 29

Figure 12. Detector Response Time vs Sensitivity —

Test Series A, Tests 6 and 7 30

Figure 13. Detector Response Time vs Sensitivity —

Test Series A, Test 8 31

Figure 14. Detector Locations — Test Series B. . . . 32

Figure 15. Detector Response Time vs Sensitivity —

Test Series B, Tests 9 and 10 33

Figure 16. Detector Response Time vs Sensitivity —

Test Series B, Test 11 34

Figure 17. Detector Response Time vs Sensitivity —

Test Series B, Tests 12 and 13 35

Figure 18. Detector Locations — Test Series C and D. 36

Figure 19. Detector Response Time vs Sensitivity —

Test Series C, Test 14 37

Figure 20. Detector Response Time vs Sensitivity —

Test Series C, Test 15 38

iv
LIST OF FIGURES (cont'd)

Page

Figure 21. Detector Response Time vs Sensitivity —

Test Series C, Test 16 39

Figure 22. Detector Response Time vs Sensitivity —

Test Series C, Test 17 40

Figure 23. Detector Response Time vs Sensitivity —

Test Series C, Test 18 41

Figure 24. Detector Response Time vs Sensitivity —

Test Series C, Test 19 42

Figure 25. Detector Response Time vs Sensitivity —

Test Series C, Test 20 43

Figure 26. Detector Response Time vs Sensitivity —

Test Series C, Test 21 44

Figure 27. Detector Response Time vs Sensitivity —

Test Series D, Test 22 45

Figure 28. Detector Response Time vs Sensitivity —

Test Series D, Test 23 46

Figure 29. Detector Response Time vs Sensitivity —

Test Series D, Test 24 47

Figure 30. Detector Response Time vs Sensitivity —

Test Series D, Test 25 48

Figure 31. Detector Response Time vs Sensitivity —

Test Series D, Test 26 49

LIST OF TABLES

Table 1. Test Series Data 8

V

a

MOBILE HOME SMOKE DETECTOR SITING STUDY

William M. Gawin and Richard G. Bright

Abstract

An investigation was conducted to evaluate

the significance of smoke detector locations to

response time for a specific set of fire conditions

in a mobile home. Parauneters having the potential

of affecting response time include: the physical

location within a mobile home such as inside wall

vs outside wall or wall vs ceiling installations;

the impact of air circulation resulting from the

operation of the heating, ventilating, and airconditioning system; and the basic detector parameter of smoke detector alarm threshold. For the

study only photoelectric-type smoke detectors were

used. These detectors utilize the Tyndall Effect

in their sensing mechanism. This limitation was

imposed to limit the number of variables. Detector

response was evaluated for fires in both smoldering

and flaming modes. The results of the study provide a case for wall installations as opposed to

ceiling installations. Further, inside wall installations may be marginally superior to outside wall

installations. The most significant finding of

the study suggests that, when in operation, the

forced-air circulating system has a major delaying

effect on detector response time to a given fire

size.

Key words: Detector sensitivity; fire detectors;

mobile homes; photoelectric smoke detectors; smoke

detector installation; smoke detector placement;

smoke detectors.

1. INTRODUCTION

The 1973 edition of the National Fire Protection Association's (NFPA) Standard for Mobile Homes, NFPA No. 50 IB

(ANSI A119. 1-1974) [I]-'- required, for the first time, the

installation of a smoke detector immediately outside of each

separate sleeping area. A sleeping area was defined as a

Bracketed numbers refer to references located at the end of

this paper.

1
bedroom or group of bedrooms not separated by a common-use

area. But in some cases, bedrooms adjoin a common corridor,

which may be as long as 6.1 m (20 ft).

Specific guidance was not provided as to the precise

location for the smoke detector, other than to state it

should be on or near the ceiling. Reports from the field

indicate that mobile homes in the marketplace have detectors:

installed on ceilings; on inside walls; on outside walls; at

either end of the common corridor; or somewhere in between.

In one case, it was noted that the requisite detector was

installed in one of the bedrooms.

The location of the smoke detector may have a significant effect on its ability to detect a fire in the shortest

possible time. The location is further conditioned by the

fact that the objective of the smoke detector requirement

was to give a measure of early warning to the sleeping occupants of a mobile home from fires occurring in the commonuse areas.

In an effort to determine the optimum location for a

smoke detector of the photoelectric type, a series of fire

tests was conducted in a mobile home comparing the response

times of a number of detectors in various locations to fires

in the common-use area. Two additional parameters were

studied concurrently. These included detector sensitivity,

that is, alarm threshold, and the effect of the air circulation portion of the heating, ventilating and air conditioning

system (HVAC) . The specific objectives of this study were:

1. to evaluate smoke detector response time based on

location in the hallway of a mobile home,

2. to observe the effect of the HVAC system on the

response time of a smoke detector,

3. to evaluate the relative merits of inside wall vs

outside wall installation,

4. to evaluate the relative merits of ceiling vs wall

installation, and

5. to examine the significance of detector sensitivity

to response time for a specific set of fire conditions .

The study involved only photoelectric-type smoke detectors which utilize the Tyndall Effect in the sensing mechanism.

All detectors were manufactured by the same corporation and

were the same model. The intent was to eliminate a variable

which could be introduced by the use of more than one type

of smoke sensing mode.

2
2. DESCRIPTION OF TEST SETUP

2.1. Test Enclosure

The mobile home used in this study was a two-bedroom

model with sleeping and common-use areas at opposite ends of

the unit (see fig. 1) . The home was obtained from the

Department of Housing and Urban Development. It had been

occupied by a family which was displaced during serious

flooding in Pennsylvania following Hurricane Agnes of 1972.

The mobile home contained the usual furnishings, appliances

and draperies normal to a mobile home. The exterior of the

home may be seen in figure 2.

In those tests where air circulation was desired the

blower of the HVAC system was used. No attempt was made to

alter the internal temperature of the mobile home with the

system. In addition, it was assumed that the airflow patterns

of the HVAC system met the requirements of ANSI A119.1,

"Mobile Homes."

All smoke detectors used were of the photoelectric-type.

These units are listed by Underwriters' Laboratories, Inc.

and are commercially available through normal retail outlets.

The detector utilizes the Tyndall Effect in sensing smoke

(see fig. 3) . Specifically, smoke enters the sensing

chamber of the detector after traveling through a specially

designed labyrinth which serves to trap light from sources

external to the detector. Between the labyrinth and the

sensing cheunber is a foamed plastic filter. The sensing

chamber contains a light source at one side which projects a

narrow beam of light across the chamber into a light trap at

the other side. A photocell is located approximately halfway

across and to one side of the chamber and is directed toward

the void space through which the light beam passes. The

angle of intersection between the axis of the photocell and

light beam path was a nominal 135° in the smoke detector

used in the tests. When smoke aerosols enter the sensing

chamber, those smoke particles having diameters larger than

0.3 micrometres scatter light in all directions. A portion

of the scattered light impinges on the photocell resulting

in the generation of a minute current. As the smoke concentration increases, the intensity of the scattered light

increases with a corresponding change in the output of the

photocell. When the output of the photocell reaches a

predetermined point, an alarm is triggered.

2.2. Smoke Detectors

2.2.1. Smoke Detector Type

3
2.2.2, Smoke Detector Sensitivity

Apparent smoke detector sensitivity is a function of

five parameters: sensing mechanism, smoke characteristics

(such as particle size) , velocity of the medium carrying the

smoke, alarm set-point of the detector circuitry, and detector

entry characteristics. The sensing mechanism and smoke

characteristics are related. Generally, photoelectric-type

smoke detectors are more responsive to smoke from smoldering

fires than from flaming fires due to the larger mean particle

size in the smoke aerosol from a smoldering fire. A smoldering fire generates a greater quantity of particulate in the

size range of 0.3 micrometer or larger, the size range in

which the photoelectric-type smoke detector operates [2]

.

Another factor affecting apparent sensitivity is the

smoke entry characteristic of the detector. The effect of

this parameter is directly related to the velocity of the

medium carrying the smoke particles. Essentially, this

characteristic describes the degree of difficulty which the

smoke experiences in traveling from the area immediately

outside the detector housing to the interior of the sensing

chamber. Every detector model has its own entry characteristic. Differences between characteristics are most noticeable at low air velocities, in the range developed by slow

smoldering fires. Therefore, a single model detector was

used in an effort to standardize this variable.

The actual alarm threshold of each detector used in

this study was determined in a small-scale, closed test chamber (see fig. 4) . The detectors are placed in the chamber

in an energized condition. Two smoldering punk sticks are

introduced into the chamber and air laden with smoke is circulated past the detector by means of a blower. Air velocity

in the vicinity of the detector and total smoke concentration

are carefully monitored. The smoke concentration is allowed

to increase continually until the detector reaches its alarm

threshold; the time and optical density of the smoke at alarm

are recorded. This procedure allows determination of the

alarm threshold of a specific detector with a reasonable

degree of reproducibility. The sensitivities of the detectors

used in this siting study are shown in the following table.

Values are given in percent obscuration per foot, optical

density per foot, and optical density per meter.

4
Detector Alarm Threshold Optical Density Optical Density

No. Percent Per Foot Per Foot Per Meter

1

2

3

4

5

6

2.3

1.1

2.3

3.0

1.9

1.7

0.010

0.004

0.010

0.013

0.008

0.007

0.033

0.015

0.033

0.043

0.027

0.024

Note that the sensitivities of the detectors vary between

the samples. A number of detectors having precisely the same

alarm threshold were not available at the outset of the study

although this would have made interpretation of the data more

straight forward. The variance noted above has been taken

into consideration and the results of the test series were

examined for trends rather than searching for specific conclusions from a specific test.

In all tests, smoke detectors were located in the hallway serving the two bedrooms and bath (see fig. 1) . The

requirements contained in NFPA No. 501B [1] specify the location of a smoke detector as immediately outside the sleeping areas. The configuration of rooms in this mobile home

plan provides some latitude with respect to specific detector

location. For example, no instructions are provided with regard to inside versus outside wall versus ceiling installations, or precise location in the corridor. The various test

series which follow explore the relative merits of a number

of possible locations. In accordance with the objectives of

this progreun, comparative tests were conducted which provided

an evaluation of ceiling versus wall installations, inside

wall versus outside wall installations and installations at

opposite ends of the hallway. The significant point to be

noted about installations at opposite ends of the hallway is

that the air intake for the HVAC system is at the approximate

midpoint of the hallway. That is, the HVAC intake has the

potential of affecting performance at one end of the hallway

significantly more than at the other by the intakes influence

on the flow of smoke along the corridor.

2.2.3. Smoke Detector Locations

5
3. TEST PROCEDURES

3.1. Test Fires

3.1.1. Smoldering Fires

A small, wood (pine) crib was used in each test in

which a smoldering fire source was desired. The crib was

square and nominally 20.3 cm (8 in) on a side. It contained

three layers of sticks, 1.9 cm (3/4 in) square. Two layers

contained eight sticks each, evenly spaced, so that the space

between the sticks was approximately 0.7 cm (9/32 in). The

top layer contained nine sticks, evenly' spaced, approximately

.64 cm (1/4 in) apart.

The crib used was chosen from a variety of different

designs previously examined. Since a truly smoldering fire

source was desired, the construction needed to be such that

the convected ventilation of the crib during combustion was

restricted. It was found that designs with larger spaces

between the crib members provided sufficient ventilation to

allow reradiating surfaces to reach auto- ignition temperature

and to convert to flaming. The overall size of the crib was

kept to a minimum to ensure that interior finish materials

within the mobile home would not be ignited inadvertently.

A photograph of the crib may be seen in figure 5.

A radiant heat source was used to sustain smoldering

combustion in the crib at a controlled rate. Care was taken

to ensure that a flaming mode did not occur on the underside

of the crib by observing the bottom through a mirror placed

adjacent to the crib. The heat source was a radiant furnace

of the type used in the National Bureau of Standards smoke

chamber [3] (see fig. 6) . The crib was suspended horizontally

in such a manner that the bottom surface was approximately

2.5 cm (1 in) above the heater element. A nominal 78 volts

AC was applied to the element. The time of each test was

recorded from the moment the voltage was applied.

The typical test setup is shown in figure 7. An example

of the smoke generated by the crib is shown in figure 8.

Note that a sheet metal pan 1.2 m (4 ft) square was placed

under each of the test fires to prevent ignition of the

carpeting.

A number of tests were also conducted in which the smoke

was generated by a flaming source. In each of these tests,

gasoline was used as a fuel. The fuel was placed in a metal

container which was 10.2 cm (4 in) in diameter and 14 cm

3.1.2. Flaming Fires

6
(5-1/2 in) high. A total of 500 ml of gasoline was placed in

the container prior to each test. (This resulted in the container being approximately half full.) The gasoline was

ignited with a match. The time of the test was recorded

from ignition.

3.1.3. Fire Location

In each test, the fire was located in the living room

in a corner formed by two outside walls as shown in figures

1 and 8. This location was used for both smoldering and

flaming sources.

3.1.4. Weather Condition

The weather conditions during the tests are summarized

as follows:

Test Series A, Test Nos. 1 to 8

Test Series B, Test No. 9

Test Series B, Test Nos. 10-11

Test Series B, Test Nos. 12-13

- Clear, temperature 27-29 °C

(80-85 *F)

- Partly cloudy, 27 'C (80 °F)

- Overcast, 27 *»C (80 •*F)

- Clear, 24 °C (70 °F)

Test Series C, Test Nos. 14 to 21- Clear, 29-35 *C (85-95 ^^F)

Test Series D, Test Nos. 22 to 26- Partly cloudy, 21-27 *C

(70-80 ''F)

3.2. Test Series

The tests conducted in this study are organized into four

test series. A discussion of each of these series is contained in the following sections. See table 1 for a recapitulation of all of the test series.

3.2.1. Series A

In this series, which consisted of eight tests, detectors

were all located at the same end of the corridor, immediately

outside the master bedroom at the rear of the mobile home

(see fig. 1). Each test employed a total of three detectors.

This series examined a total of five positions of installation which are shown in figure 9. Specific location with

respect to the master bedroom is identical to that shown in

figure 16.
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Each test fire in this series was a smoldering wood

crib. In Tests 1 to 7, the HVAC circulating system was not

in operation. In Test 8, the system was operating continuously throughout the test.

Detector response time vs sensitivity and location are

illustrated in figures 10 to 13.

3.2.2. Series B

In this series, consisting of five tests (Nos. 9 to 13)

,

detectors were located at the scune end of the corridor,

immediately outside the kitchen. Each test employed a total

of five detectors. Detector positions are shown in figure

14. Location with respect to the kitchen is identical to

that shown in figure 18.

In each test, a three-layer wood crib of the type used

in Test Series A was utilized to produce smoldering combustion. The HVAC system was not in operation during this test

series.

Detector response time vs sensitivity and location are

illustrated in figures 15-17.

3.2.3. Series C

In this series, consisting of eight tests (Nos. 14 to 21)

,

detectors were located at both ends of the corridor. A total

of six detectors were used in each test; three were installed

at each end of the corridor. Specific installation locations

are shown in figure 18. Designations are OR (outside wall,

rear), CR (ceiling, rear), IR (inside wall, rear), OF (outside

wall, front), CF (ceiling, front) and IF (inside wall, front).

In each test, a three-layer wood crib of the type used

in the previous test series was used to provide a smoldering

fire. In Tests 14 to 18, the HVAC circulating system was

not in operation. In Tests 19 to 21, the system was operating

continuously during the test.

Detector response time vs sensitivity and location are

illustrated in figures 19 to 26.

3.2.4. Series D

In this serie;s, consisting of five tests (Nos. 22 to 26) , detectors were located at both ends of the corridor. A total

of six detectors were used in each test; three were installed

9
at each end of the corridor. Specific installation locations

are shown in figure 18. Designations are the same as those

used in Test Series C.

In each test smoke was generated from the flaming gasoline source. Time was recorded from the ignition of the

gasoline.

In Tests 22 to 25, the HVAC circulating system was not

in operation. In Test No. 26, the system was operating

continuously during the test.

Detector response time vs sensitivity and location are

illustrated in figures 27 to 31.

4. DISCUSSION OF TEST RESULTS

4.1. Test Series A

One might assume that detector sensitivity is a major

factor in response time. Examination of the test data bears

this out. When one compares the mean response times of the

detectors of different sensitivities for the first seven

tests, the results are as follows:

Detector Sensitivity Mean Response Time

(percent per foot) (minute : second)

1/2 16:15

1 18:30

2 22:15

When one compares mean response times for detectors in

location A vs C (inside ceiling vs outside ceiling) , the

following is observed:

Tests 1-5

Mean Response Time (Minute : Second)

A C

15:00 16:40

These results seem to indicate that an inside ceiling

installation is slightly superior to an outside ceiling installation. (Tests 6 to 8 were not included because these

employed a two-percent detector on an inside wall without

data for a corresponding outside wall installation.)

10
It should be noted that response times were substantially

increased by the operation of the HVAC circulation system in

Test No, 8. The significance of the effect is apparent when

comparing mean response time for all detectors for Tests 1

to 6 with the mean response time for Test No. 8.

Mean Response Time

Condition (Minute : Second

)

HVAC off 19:00

HVAC on 32:00

13:00 - Difference

Note that the system air return grille is located between

the detectors and the fire. It appears that the blower tended

to intercept the smoke before reaching the detectors and distributed it homogenously throughout the volume of the mobile

home. The result was that a substantially greater total

volume of smoke was needed to be generated in order to bring

the entire volume to a high enough density to reach alarm

threshold

.

4.2. Test Series B

When examining the data for Tests 9, 10 and 12, and comparing the response times of detectors A and B (inside wall)

with D and E (outside wall) no significant difference can be

noted. In this test series, there does not appear to be any

significant advantage to inside wall vs outside wall installation.

If

ceiling

one compares

installation.

response time for wall installation vs

the following is noted:

Location

Mean Response Time*

(Minute : Second)

*

Wall

Ceiling

16:20

20:00

3:40 - Difference

For Tests 9 and 10.

11
Thus, it appears that the wall installation results in

more rapid detection than the ceiling installation in this

test series. Test No. 11 was not included because the crib

went to the flaming mode of combustion at approximately 4

minutes and the test was terminated shortly thereafter.

Test No. 12 was not included because, inadvertently detectors

D and E were not energized prior to the test. However, of

the detectors which did alarm, the ceiling installation had

the longest response time by 2 minutes. In Test No. 13, no

alarm was experienced by the ceiling mounted detector at 30

minutes and the test was terminated. All other detectors

had been in alarm for at least 5 minutes.

Also, it was noted in this test series that there was

no appreciable difference in response time between those

detectors installed 7 cm (18 in) from the ceiling and those

installed 3.5 cm (9 in). Apparently, in this smoldering

fire test series, the smoke layer had sufficient depth below

the ceiling to reach both the upper and lower detectors

simultaneously.

4.3. Test Series C

With a fire occurring in a common-use area of the mobile

home and detectors installed at a variety of locations in

the corridor, one would anticipate that those detectors

closest to the fire would alarm first. This assumption is

borne out by the data from the smoldering fires in this

test series. Mean response times for installations at the

opposite ends of the corridor is as follows:

Mean Response Time

Location (Minute : Second

)

Kitchen end 22:30

Bedroom end 26:45

4:15 - Difference

in Test Series A, data seemed to indicate that an inside wall installation would be somewhat superior to an outside wall installation. This does not seem to be confirmed

in this test series. Data comparing these two locations

follows:

12
Location

Mean Response Time

(Minute : Second

)

Inside Wall

Outside Wall

23:50

23:40

0:10 - Difference

This data does not indicate an advantage to either location. It should be noted, however, that these tests were

conducted under summer conditions with interior temperatures

approximately equal to outside temperatures. The result was

that temperatures of inside walls and outside walls were

approximately the same.

It is of interest to compare the results of ceiling vs

wall installation. The following mean response time comparison shows that a wall installation is substantially

superior to a ceiling installation for a slow, smoldering

fire.

Mean Response Time

Location (Minute : Second

)

Wall 23:45

Ceiling 26:20

2:35 - Difference

Finally, note the effect of the HVAC circulating system

in this test series with that experienced in Test No. 8

described earlier. The following table compares the effect

of the HVAC system on response time:

Mean Response Time

Condition (Minute : Second)

HVAC off 21:40

HVAC on 29:20

7:40 - Difference

13
In general, this data confirms the experience from the

earlier test series.

4.4. Test Series D

In this test series, which were all flaming gasoline

fires with black smoke, comparison of response times for locations at each end of the hallway, indicate an apparent

anomaly. It appears as though the detectors at the far (bedroom) end of the corridor had a shorter mean response time

than those at the kitchen end. In this case, it is apparent

that detector sensitivity may be more important than location

within the limits of the test parameters. Additionally, the

velocity of the smoke was greater because of the greater

thermal energy of the flaming fire. This greater velocity

would serve to minimize the effect of distance between

locations

.

When a comparison is made of response times for inside

wall locations vs outside wall locations, it appears as

though the inside wall provides slightly superior response

times than does the outside wall. The following shows a

comparison between the two.

Location

Mean Response Time

(Minute : Second

)

Inside wall - front and rear

Outside wall - front and rear

14:00

15:05

1:05 - Difference

The performance of ceiling vs wall installations for a

flaming as opposed to a smoldering fire can be compared next.

In the flaming case, the ceiling installation is superior

apparently because sufficient thermal energy is available to

break through the boundary layer near ,the. ceilinjg. Additionally, boundary layer conditions tend to be minimized under

higher velocity conditions. A comparison of these two locations follows:

14
Location (Minute : Second)

Wall 14:30

Ceiling 12 : 05

2:25 - Difference

Finally/ it is again possible to examine the effect of

the HVAC ventilating system on the performance of the detectors, this time with a flaming fire. As in earlier tests,

the effect of the system was dramatic in the manner which

detector response times were increased. A comparison of the

data gathered in this test series follows:

Mean Response Time

Condition (Minute : Second)

HVAC off 12:20

HVAC on 19:20

7:00 - Difference

If one examines the mean response times of detectors at

opposite ends of the corridor with the HVAC system on, one

finds that those units at the kitchen end of the corridor

had substantially shorter response times than those at the

bedroom end when the HVAC system was in operation, as

indicated in the following table:

Mean Response Time

Location (Minute : Second)

Kitchen end 16:10

Bedroom end ' 22:05

5:55 - Difference

Note also that the detectors at the kitchen end had a

substantially longer mean response time than that for all

detectors without the HVAC in operation. This would seem to

indicate that the response of all detectors is delayed when

the HVAC system is in operation, regardless of location of

installation.

15
Finally, of all the parameters examined, the circulating system had the most significant effect on detector performance. The data also indicates that the results were

reasonably consistent.

4.5. Weather Conditions

It is interesting to compare the response characteristics of detectors based on location with general weather conditions at the time of the test. For example, Test Nos. 12-21

were conducted during a period of generally clear weather.

In examining the data, note that with the exception of Tests

20 and 21, the response times of the ceiling mounted detectors

were longer than that of the wall mounted detectors. Conversely, in Tests 9-11 and 22-26, the weather was generally

cloudy and it may be observed that the ceiling mounted detectors generally performed better than wall mounted units.

Evaluation of weather as a test parameter was not planned at the outset of the investigation. Accordingly, the

test series was not structured so that definitive conclusions

could be drawn from the results. However, the effect of the

sun's heating of the roof/ceiling assembly may be the major

reason for the poorer performance of the ceiling detectors

with respect to the wall detectors.

5. CONCLUSIONS

In line with the objectives of this siting study, the

following conclusions have been reached from an examination

of the data presented in this report.

1. In mobile homes employing a floor plan similar to

the one used in this study, it appears as though the

best general location for a smoke detector is at the

end of the corridor entering the common-use areas of

the home. Generally, this location appears to offer

the shortest response time to fires originating in

the living room area and perhaps the dining/kitchen

areas as well.

2. The effect of the HVAC circulating system was more

significant than anticipated prior to this study.

In each case, the system delayed the response of

the smoke detectors, regardless of location within

the corridor. Even those detectors installed between the incipient fire and the intake for the

HVAC system, i.e. the kitchen end of the corridor,

will have their response times increased by operation of the HVAC system. The conclusion is that

16
an incipient fire which occurs during the operation

of the system is a more serious hazard than one

which occurs when the system is not in operation.

(In addition to the alarm delay, there is a more

rapid distribution of smoke and potentially toxic

combustion products throughout the home.) It is

not possible to predict precisely the effect of

a HVAC system having a location other than in

the corridor, as in this test program. It is

likely, however, that any HVAC system, if in operation, will have a similar delaying effect on the

response of smoke detector in the event of a fire

in the mobile home.

3. When examining the results of Test Series A with

Test Series B, it appears that in one case an inside

wall installation is marginally superior to an outside wall installation. In the other case, the

opposite seems true. Considering all data, however,

it does not appear that this report can demonstrate

that one location is consistently superior to the

other. Again, it should be noted that these tests

were conducted under summer conditions with the result that temperatures of internal walls and external walls were approximately the same. Unpublished

test data from another source [4] for tests conducted

under winter time conditions indicate that under

winter conditions smoke detectors installed on

exterior walls are slower to respond than smoke

detectors on interior walls.

4. It appears that in the case of ceiling vs wall

installation, relative performance relates to the

type of fire. Slowly developing, smoldering fires

seem to be detected more easily by detectors installed on a wall a short distance below the ceiling.

Flaming fires have more thermal energy and appear

to be more easily detected by a ceiling installation.

Since some evidence has been presented by other

studies which indicates that a-higher percentage of

fires in the home start in the smoldering rather

than in the flaming mode, a wall installation would

seem preferable.

5. It was anticipated prior to the study that more

sensitive detectors would have a shorter response

time to a given fire than less sensitive ones. This

was particularly evident during the smoldering

fire test series. This difference in response times

would be amplified during the operation of the HVAC

circulating system since smoke is mixed somewhat

homogenously during its operation. It would appear

17
then for the earliest alarm indication of fire, smoke

detectors with the highest degree of sensitivity

should be used. However, the sensitivity of the

detector will have to be balanced against a possible

increase in false alarms. What this balance is or

how to arrive at this balance, particularly for

photoelectric-type smoke detectors as used in this

test series, has not been satisfactorily determined

at the present time.

6 . REFERENCES

[1] National Fire Protection Association's (NFPA) Standard

No. 501B, Standard for Mobile Homes, 1973 Edition.

Also American National Standards Institute Standard

ANSI No. A119. 1-1974.

[2] Scheidweiler , A., New Research in Fire Detection

Technology. International Symposium (1968)

.

[3] Lee, T. G., Inter laboratory Evaluation of Smoke Density

Chamber, Nat. Bur. Stand. (U.S.), Technical Note 708

(Dec. 1971).

[4] Private communication, G. Rork, Honeywell.

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49
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 76-1016

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

MOBILE HOME SMOKE DEIECIOK olllNo biUUi

5. Publication Date May 1976

6. Performing Organization Code

7. AUTHOR(S)

William Gawin and Richard Bright

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 492 8677

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9

13. Type of Report & Period

Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual aummary of moat significant information. If document includes a significant

bibliography or literature survey, mention it here.)

An investigation was conducted to evaluate the significance of

smoke detector locations to response time for a specific set of fire

conditions in a mobile home. Parameters having the potential of

affecting response time include: the physical location within a mobile

home such as inside wall vs outside wall or wall vs ceiling installations; the impact of air circulation resulting from the operation of

the heating, ventilating, and air-conditioning system; and the basic

detector parameter of smoke detector alarm threshold. For the study

only photoelectric-type smoke detectors were used. These detectors

utilize the Tyndall Effect in their sensing mechanism. This limitation

was imposed to limit the number of variables. Detector response was

evaluated for fires in both smoldering and flaming modes. The results

of the study provide a case for wall installations as opposed to ceiling installations. Further, inside wall installations may be marginally

superior to outside wall installations. The most significant finding

of the study suggests that, when in operation, the forced-air circulating

system has a major delaying effect on detector response time to a given

fire size.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only Oie first letter of (he first key word unless a proper name; separated by semicolons) Detector sensitivity; fire detectors ; mobilie. homes ;

• photoelectric smoke detectors; smoke detector installation; smoke

detector placement; smoke detectors.

18. AVAILABILITY E Unlimited

1

' For Official Distribution. Do Not Release to NTIS

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' Order From Sup. of Doc, U.S. Government Printing Office

Washineton. D.C. 20402. SD Cat. No. C13

pC 1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22I5I

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