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 project

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 models

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 Model I.

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 method.

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 prediction model.

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. What's next 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 project.

Notes:

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 library@nfpa.org for more information.