The Results of a Major Upholstered Furniture Fire Study
by Vytenis Babrauskas, Ph.D.
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Because furniture fires contribute to so many fire deaths throughout
the world, the European Commission decided to conduct a comprehensive research
project to measure the hazard they present.
Upholstered items, such as furniture and mattresses, play a special role
in fire hazards. In fact, a 1976 study of NFPA's FIDO database concluded
that fires started in these items constitute the single largest cause of
fire deaths in the United States.(1) Although their number has decreased
in the intervening years, furniture fires still rank among our top contributors
to fire deaths.
The largest fraction of upholstered furniture fires is started by lighted
cigarettes, which may cause either smoldering or flaming fires. Smoldering
furniture releases toxic combustion gases very slowly, but this can be enough
to kill occupants if they're asleep and exposed to such gases for a long
time. More often, a fire that begins by smoldering will eventually burst
into flames, and when flaming starts, combustion products are generated
at a much greater rate-which means that the hazard to occupants also increases
substantially. The fraction of lethalities that occur during the initial
smolder phase of such fires versus those that occur during flaming hasn't
been quantified, however.
Other furniture ignition scenarios, such as children playing with matches,
involve fires that actually begin in the flaming stage. If such fires occur
in a small room, escape may become impossible after only a few minutes.
The hazards associated with flaming furniture fires were systematically
quantified in the early 1980s, when researchers at the National Institute
of Standards and Technology (NIST) conducted extensive experimental work
on the subject. These findings, issued as a NIST monograph, summarized much
of the knowledge of furniture fires up to the early 1980s and presented
quantitative measurement and predictive methods.(2) The measurement methods
comprised the room fire test and the furniture calorimeter test for full-scale
test items and the cone calorimeter for bench-scale testing. A prediction
method was also presented, allowing the use of bench-scale cone calorimeter
data to predict full-scale furniture fire behavior.
The 1985 NIST study, while a landmark in the field, was already dated
by the 1990s. The materials studied in the 1980s were rather different from
those available in the next decade. In particular, fire-protective interliners,
whose value is appreciated today, weren't often used back then. In addition,
the experimental work with the cone calorimeter and the furniture calorimeter
had been conducted right after these two instruments were invented, so a
user base of experience such as we have today was then unavailable. Finally,
the scope of work was limited: Only a few types of furniture were examined,
and only a limited amount of fire modeling was undertaken.
Such considerations led the European Commission to decide that a comprehensive
research project was needed to quantify the hazard of flaming upholstered
furniture fires. The commission set up a two-year project, conducted during
1993 and 1994, with a budget of about $3 million, making it one of the largest
fire research projects of any kind. Eleven laboratories from eight European
countries participated in the study, which was finished in 1995. Engineering
details for this work have been published in the technical literature, and
the complete study has been issued as a 400-page hardbound book.(3,4,5,6)
The CBUF tool
The output of the project on combustion behavior of upholstered furniture
(CBUF) can simply be expressed as the CBUF Tool, as shown in Figure 1. The
end objective is to arrive at a design for an item of upholstered furniture
that's satisfactory from the point of view of fire safety. To reach this
objective requires testing, which can be either a full-scale test in the
furniture calorimeter or a bench-scale test.
In the full-scale test, the user needn't do any modeling, since the required
results-peak heat release rate (HRR)-are given directly. For reasons of
cost and expedience, however, most users will prefer bench-scale testing.
In that case, the materials that make up the upholstery system must be made
into a 10- by 10-centimeter bench-scale composite that's tested in the cone
calorimeter (see Figure 2).
The normal cone calorimeter tests involve making a test specimen of all
of the layers as they're present in the product because, until now, it was
generally considered impossible to predict the performance of multilayered
products by testing the layers separately. The techniques simply weren't
available to put together results that could be used to predict the way
the real composite would behave. Perhaps the most innovative result of the
CBUF is a method for testing the components of an item in the cone calorimeter
in order to predict the behavior of the composite (see left-hand branch
of Figure 1). This is important to manufacturers, since testing fabrics
and fillings separately can be much simpler than testing every combination
as a composite.
The CBUF work resulted in three models for using the input data of the
cone calorimeter and predicting the peak HRR, the untenability time, and
other aspects of the full-scale furniture fire. These models range from
Model I, which can be implemented on a spreadsheet, to Model III, which
requires a computer program to solve its advanced mathematics.
As an example of the type of model output obtained, Figure 3 shows the
prediction of the peak HRR according to the procedures of Model I. The predictions
are very good, and the errors tend to lie on the conservative side. Figure
4 shows the Model II prediction of the detailed time-HRR history of an upholstered
chair and compares it to the experimentally measured HRR. Model II uses
more sophisticated mathematics than Model I, so it can predict not only
the peak HRR, but also the shape of the HRR curve. Model III was developed
specifically for predicting mattress fires. Figure 5 compares its predictions
to experimental results. Of the two model variants shown, the one using
exact scaling produces very close results until late in the fire.
The European Commission wanted researchers to focus particularly on the
amount of time an occupant in the room of fire origin would have to escape.
The commission also wanted to know whether a separate test for combustion
toxicity would be required to properly evaluate the toxicity effects, so
CBUF researchers conducted detailed toxicity assessments of many of the
nearly 1,500 tests run. In addition, they modeled the fire to relate the
furniture calorimeter HRR output to untenability conditions in a room.
The results established that occupants whose heads were in a hot gas
layer would have little chance of survival, while occupants below this hot
layer-those who bent over or dropped to the floor-could be expected to escape.
Thus, researchers considered the point at which the hot gas layer dropped
to 1 to 1.2 meters above the floor to be the acute danger point. Extensive
modeling work then established that, for a room the size of a small bedroom-fires
become dangerous more slowly if the room is large-this layer height corresponds
to a peak HRR value of 400 kW.
Further studies showed that separate testing for gas toxicity wasn't
necessary. The occupants' escape potential could be assessed solely by determining
how long it took the layer to descend to 1 to 1.2 meters above the floor.
This simplified testing requirements considerably, since only HRR had to
be measured or predicted, and additional tests weren't required. The time
to incapacitation, in turn, could be modeled using the techniques developed
in CBUF. Figure 6 shows the predictability of the untenability time using
Perhaps the most challenging task was to predict the cone calorimeter
composite behavior by testing only individual components. To ensure that
highly controlled, representative cone calorimeter testing could be done
on furniture composites, researchers developed an improved specimen preparation
Such composite testing will always interest researchers and manufacturers
trying to understand their products at the most fundamental level. If the
CBUF Tool is to be useful to industry for routine work, however, an even
simpler alternative must also be available. It turns out that, although
the procedure needed to do this was quite complex mathematically, the details
could be hidden from the user by setting up a specialized computer program
that would analyze the experimental results and derive the predicted composite
behavior. Figure 7 shows typical predictions obtained using the component-to-composite
Robustness of test methods
The CBUF Tool wouldn't be useful if its methods weren't precise, repeatable,
and reproducible, so a great deal of effort went into developing detailed
test instructions for cone calorimeter, furniture calorimeter, and room
fire testing. The success of these testing instructions was evaluated by
means of round-robin procedures.
For the cone calorimeter, for example, it was found that the repeatability
and reproducibility of testing furniture composites were similar to those
established earlier for building products. Because building products don't
require the careful preparation of the soft, multilayered items involved
in furniture construction, the fact that the results were similarly precise
indicates that the test procedures were, indeed, successfully controlled.
Applying the results
The results of the CBUF program will now be considered in Europe in the
context of the debate on the fire safety levels necessary for furniture
in European countries. However, the technical output should be extremely
valuable for those interested in fire safety everywhere, including the United
States. These results can be used by any country, institution, or manufacturer
interested in making furniture fire-safe.
The work of CBUF has vastly improved our knowledge of furniture fires.
Nonetheless, we must remember that fire is an exceedingly complex phenomenon
and that there's no such thing as a complete answer when it comes to predicting
its effects. The CBUF research provided only preliminary, not definitive,
answers to questions about the fire behavior of certain types of furniture,
such as mattresses and plastic-shell-type office chairs.
And the CBUF research only partially explored the behavior of the highly
fire-improved types of chairs prescribed in California for certain applications.
However, both the models and the test procedures developed in CBUF studies
are expected to be of significant help to researchers trying to the solve
furniture fire problem in the future.
--note: The boxed text below appeared as a sidebar
in the original article--
Upholstered Furniture and CPSC: A Look at What's Happening
As a result of a petition submitted by the National Association of State
Fire Marshals (NASFM), the Consumer Product Safety Commission (CPSC) is
conducting a project to develop a voluntary or mandatory flammability safety
standard addressing fire risks associated with small, open-flame ignitions
of upholstered furniture and to evaluate the level of industry conformance
to existing voluntary cigarette-ignition resistance guidelines. CPSC's Advance
Notice of Proposed Rulemaking (ANPR) on small, open-flame fire risks was
published in the Federal Register in 1994.
What's going on now
Currently, the CPSC staff is working in several areas. CPSC's regional
offices are investigating open-flame fires through 1996 in an effort to
collect data on the causes and ignition scenarios of such fires to provide
a partial basis for estimating the potential lifesaving and other benefits
of safer furniture.
An industry survey of furniture manufacturers is also being conducted
to obtain information on furniture construction and materials currently
on the market. This study will help estimate the scope and possible costs
of a standard.
Testing and technical development work to determine the feasibility of
potential safety improvements is also under way. Full-scale open-flame testing
of 27 chairs, recently completed, examined three ignition locations: dust
covers, skirts, and seating areas. CPSC also developed draft small-scale
test methods and a test fixture for the locations examined in the full-scale
tests. An interlaboratory program is planned for 1996 to establish the repeatability
and reproducibility of the small-scale test, which may yield promising approaches
for a voluntary or CPSC-proposed standard.
In addition, CPSC is evaluating industry conformance to the voluntary
program of the Upholstered Furniture Action Council (UFAC), which is aimed
at reducing cigarette ignition fires. Full-scale and component tests of
cigarette ignition resistance on 58 pairs of chairs are nearly complete.
CPSC will use these and other data to determine whether any action is needed
to address cigarette ignition risks.
CPSC staff continues to solicit input from all interested parties, including
the fire safety community, government organizations, consumer groups, and
industry organizations representing upholstered furniture products and suppliers
of foam fillings, chemicals, and fabrics. Several such groups are providing
valuable technical data and other information.
CPSC will continue to monitor voluntary safety efforts and to develop
information necessary to support a voluntary standard or a mandatory rule.
CPSC will also evaluate the possible costs and benefits of a proposed rule
and its alternatives. The cigarette testing and evaluation program will
form the basis for a CPSC decision on the issue of smoldering ignition.
CPSC will consider a briefing package summarizing the available technical
information and responding to the public comments on the ANPR in late 1996
or early 1997. The commission must decide whether to issue a Notice of Proposed
Rulemaking, the second step in the standard-development process. If issued,
this notice will include a proposed standard incorporating a draft test
method and a preliminary cost analysis. The commission must also decide
whether to grant the remaining portion of the petition from NASFM regarding
the hazard of fires started by cigarettes. For both issues, a voluntary
program that adequately reduces the risk may be a reasonable alternative
to a mandatory rule.
Vytenis Babrauskas, Ph.D., is president of Fire Science and Technology,
Inc. in Kelso, Washington. He acted as technical consultant to the CBUF
1. F. Clarke, II and J. Ottoson, "Fire Death Scenario
and Firesafety Planning," Fire Journal, Vol. 70, No. 3 (May 1976),
pp. 2022 and 117118.
2. V. Babrauskas and J. F. Krasny, "Fire Behavior
of Upholstered Furniture," NBS Monograph 173, U.S. National Bureau
of Standards, 1985.
3. V. Babrauskas, D. Baroudi, J. Myllymki, and M. Kokkala,
"The Cone Calorimeter Used for Predictions of the Full-Scale Burning
Behaviour of Upholstered Furniture," Proceedings of the Fourth International
Fire and Materials Conference, Interscience Communications Ltd., London,
1995, pp. 203217.
4. J. Myllymaki and D. Baroudi, "Prediction of Heat
Release Rate of Upholstered Furniture Using Integral Formulation,"
InterFlam '96, Interscience Communications Ltd, London, 1996, pp. 2735.
5. D. Baroudi, and M. Kokkala, "Flame Spread and Heat
Release Rate Model for a Burning Mattress," InterFlam '96, Interscience
Communications Ltd, London, 1996, pp. 3746.
6. B. Sundstrom, ed., Fire Safety of Upholstered Furniture:
The Final Report on the CBUF Research Programme (Report EUR 16477 EN), Directorate-General
Science, Research and Development (Measurements and Testing) of the European
Commission (1995), distributed through Interscience Communications Ltd,
24 Quentin Rd., London SE13 5DF, England.
Reprinted from NFPA Journal, July/August 1996,
p 84-88. Reprinted by permission of NFPA Journal.
Please contact the NFPA Library (617) 984-7445 or e-mail firstname.lastname@example.org
for more information.