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Executive Summary

According to estimates by the National Fire Protection Association and the U. S. Fire

Administration, U. S. home usage of smoke alarms rose from less than 10 % in 1975 to at least

95 % in 2000, while the number of home fire deaths was cut nearly in half. Thus the home

smoke alarm is credited as the greatest success story in fire safety in the last part of the 20th

century, because it alone represented a highly effective fire safety technology with leverage on

most of the fire death problem that went from only token usage to nearly universal usage in a

remarkably short time. Other highly effective fire safety technologies either affect a smaller

share of the fire death problem (e.g., child-resistant lighter, cigarette-resistant mattress or

upholstered furniture) or have yet to see more than token usage (e.g., home fire sprinkler,

reduced ignition-strength cigarette).

A seminal component that underpinned this success was the existence of a comprehensive,

independent set of tests conducted in 1975-76 that clearly demonstrated the potential of smoke

alarms to save lives. These were the so-called Indiana Dunes tests sponsored by The National

Institute of Standards and Technology, NIST, (then the National Bureau of Standards) and

conducted by Illinois Institute of Technology Research Institute and Underwriters Laboratories.

In the past few years questions were being raised about the efficacy of some smoke alarm

technologies, whether the numbers and locations in homes still represented the optimum

configuration, and if multi-sensor designs (as are becoming popular for commercial fire alarm

systems) might perform better or produce fewer nuisance alarms. Some simply thought that it

was time to reexamine the technology in light of its importance to public safety. To this end a

consortium of four federal agencies and Underwriters Laboratories (with in-kind support from

several others) funded this project.

The present work followed a design similar to that used in the Indiana Dunes tests. Tests were

conducted in actual homes with representative sizes and floorplans, utilized actual furnishings

and household items for fire sources, and tested actual smoke alarms currently sold in retail

stores. Smoke alarm performance was quantified in terms of the escape time provided by groups

of alarms installed in accordance with typical code provisions. While some of the smoke alarms

were modified by their manufacturers to provide continuous, analog output from their sensors

(which allowed the analysis of the performance of multi-sensors and decision algorithms) these

were compared to identical models purchased from retail stores and included in all tests. 

Additionally a separate study of nuisance alarm sources was conducted because this was

identified as an important issue in a prior study by the U.S. Consumer Product Safety

Commission.
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The fire emulator/detector evaluator (FE/DE) is a single-pass "wind tunnel" at NIST designed to

reproduce all relevant conditions needed to assess the performance of spot-type particulate,

thermal and gas sensor detectors or combination detectors. Specifically, the FE/DE allows for

the control of the flow velocity, air temperature, gas species, and aerosol concentrations at a test

section wherein detectors and sensors are exposed to these environmental conditions . Included

in this report are complete data from tests conducted in the FE/DE apparatus and calibrations for

all of the alarms and detectors used in this study. Calibration in the FE/DE of the alarms used in

the current study showed that the sensitivity of the alarms was consistent with manufacturer

ratings and, on average, of equivalent sensitivity to those used in the 1975 study. The average

sensitivity measured for all alarms tested was 5.1 %/m ± 1 %/m (1.5 %/ft ± 0.4 %/ft). In the

1975 study, the average of all alarms tested was 6.3 %/m ± 2 %/m (1.9 %/ft ± 0.7 %/ft). While

the average for the 1975 tests is higher, the uncertainty in the data overlaps.

An analysis of residential fire statistics was conducted for this study to identify the important fire

scenarios that were included in the study. Flaming and smoldering upholstered furniture and

mattresses account for the top four most deadly fire scenarios. Flaming cooking materials are

involved more than five times more frequently than any other material. These scenarios included

the top five ranked by number of deaths, and among the top ten ranked by frequency of

occurrence. 

Fire produces heat, smoke, and toxic gases, all of which can threaten human life. In these

experiments environmental parameters that have an impact on human response were measured.

Parameters include temperature rise, toxic gas production, and smoke obscuration. Aspects of

these that can be measured directly include the gas temperature, mass loss of the burning item,

species concentrations, including CO, CO2, O2, and other gases. Two different geometries of

residential structures were used for the tests. The manufactured home geometry represented an

array of residential layouts. The arrangement of the manufactured home was sufficiently generic

as to represent an apartment, condominium, or small ranch house, in addition to a manufactured

home, although it did include a sloped ceiling throughout the structure. The primary partitioning

of the 84.7 m2 (911 ft2) home consisted of three bedrooms, one full bathroom, one kitchen/dining

area, one living room, and two hallways. The 139 m2

 (1495 ft2) two-story home was a brickclad 3 bedroom home. The first floor consisted of a foyer, den, family room, kitchen, dining

room, bathroom, and stairwell to the upstairs. The home did not have a basement. The 2-car

garage was accessible from the first floor den. The second floor consisted of a stairwell to the

downstairs, hallway, 2 bathrooms, and two smaller bedrooms and one master bedroom. A total

of 36 tests were conducted in the two homes; 27 in the manufactured home, and 8 in the 2-story

home.

The experimental design provided data on the performance of alarms in various installation

arrangements. Groups of alarms were located in the room of fire origin, at least one bedroom,

and in a central location on every level. Thus, by considering the alarm times of devices in

various locations against tenability times for any test it was possible to determine the escape
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time provided by various installation arrangements including every room, every level with or

without every bedroom, and single detectors. Since both ionization and photoelectric types were

included at each location the performance by sensor type was also quantified.

Smoke alarms of either type installed on every level generally provided the necessary escape

time for different fire types and locations. Adding smoke alarms in bedrooms increased the

escape time provided, especially for smoldering fires. These tests quantified an increased escape

time for fires starting in the bedroom. 

The results obtained were similar to those of the earlier work. Both common residential smoke

alarm technologies (ionization and photoelectric) provided positive escape times in most fire

scenarios with the ionization type reacting earlier to flaming fires and the photoelectric type

reacting earlier to smoldering fires. The main difference from the earlier work is that the amount

of escape time provided is consistently less. For example, average times to untenable conditions

for flaming tests was 3 min compared to 17 min in the prior work. While some of this difference

may be attributed to the tenability criteria used in the current study, it is also clear that fire

growth in the current tests are significantly faster than in the earlier tests. For flaming fires, time

to alarm activation and measurement of elevated temperatures in the room of fire origin support

this faster fire growth observation. However, the smoldering fire scenarios are very difficult to

reproduce experimentally and tenability times in the present study have an uncertainty (based

upon one standard deviation) which overlaps the uncertainty from the 1975 study. Therefore,

caution should be exhibited in drawing conclusions based upon comparisons of smoldering

tenability times between the two studies. It is important to note that while both the 1975 study

and the current study attempted to use a representative sample of available and important

furnishings, each study included only a small fraction of those available in the marketplace. 

Still, this study is consistent with other recent studies of furniture and mattresses, even though

there may be significant differences in the burning behavior between items of furniture. 

Activation times for other fire detection technologies were also collected. As expected, CO

alarms respond best to fires which produce considerable quantities of carbon monoxide during

the combustion process, i.e., smoldering fire scenarios and the closed-door flaming mattress

(which smoldered after the room of fire origin became oxygen limited). Tell-tell sprinklers and

heat alarms responded to the flaming fire scenarios as well as to the smoldering fire scenarios

after a transition to flaming combustion. Activation times of these devices support the current

practice of use only in conjunction with smoke alarms.

Nuisance alarms in residential settings from typical cooking activities, smoking or candle flames

are affected by the properties of the aerosol produced and its concentration, the location of an

alarm relative to the source, and the air flow that transports smoke to an alarm. This is not

surprising, as the same observations have been made in the fire tests here and other studies. This

study provides a detailed set of data that can be used to address several issues involving nuisance

alarms and reinforces current suggested practices. Clearly, the advice that alarms not be
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installed close to cooking appliances if at all possible is valid. These results show that

homeowners who are able to move the location of an alarm that frequently experiences nuisance

alarms would do well to maximize its distance from cooking appliances while keeping it in the

area to be protected. It was observed that ionization alarms had a propensity to alarm when

exposed to nuisance aerosols produced in the early stages of some cooking activities, prior to

noticeable smoke production. This phenomenon could be particularly vexing to homeowners

who experience such nuisance alarms. Carbon monoxide electrochemical cells at all alarm

locations gathered data on the level of carbon monoxide produced during the tests and

transported to the alarms. These data in conjunction with the complete fire test series data could

be used to verify combined smoke/CO alarm algorithms.

The FE/DE nuisance source tests captured salient features of some of the manufactured home

tests. More work needs to be done to produce a set of tests and the performance criteria that

covers a significant range of residential nuisance sources, and would assure a benefit in terms of

nuisance alarm reduction. This work is part of ongoing research with the FE/DE at NIST. The

nuisance alarm study also represents a wealth of data valuable in establishing (amazingly for the

first time) test methods and criteria for what a smoke alarm should not respond to. Testing labs

are examining NIST's unique FE/DE apparatus to replace the current, product specific test

apparatus that do not allow multi-sensor devices to be evaluated. 

The present work has produced an extensive database of documented data on typical residential

fires. All data collected in the tests are available in electronic form (http://smokealarm.nist.gov)

and are already being used by the smoke alarm industry to improve their products, by the

product approval agencies to improve testing procedures, and by researchers to validate and

improve fire models. 

The present work has considerable potential for communicating important fire safety messages

to the public. The material has been made freely available and NIST plans to produce examples

and is willing to work with others wishing to do the same.