Issue 39: Evaluating the Fire Threat from Upholstered Furniture
By Charles Fleischmann, Ph.D., P.E.
When an unwanted fire occurs within non-storage buildings, there are
few objects that have the potential to bring about untenable conditions
as swiftly as upholstered furniture and mattresses. In the worst case
scenario, the heat release rate (HRR) of an upholstered furniture item
can reach values greater than 3 MW in a very short period of time (3-5
minutes) following ignition.1 Furthermore, it is not only the
heat given off during the growth period, but also the toxic combustion
products (primarily CO) produced that can overwhelm the occupants.
Over the last three decades, there has been a great deal of research
and regulation on upholstered furniture and mattresses, which makes
upholstered furniture and mattresses some of the most widely studied
fuel packages available to fire protection engineers. In Europe, the
Combustion Behaviour of Upholstered Furniture2 (CBUF) study incorporated both experimental results as well as enhanced fire modeling.
Yet, much of this modeling effort is nearly obsolete with the
advances made in numerical modeling. Outside of the research
environment, the Consumer Product Safety Commission (CPSC) in the USA
has been investigating the hazard posed by upholstered furniture and
mattresses. As part of this work, CPSC has carried out a number of
experiments on both upholstered furniture and mattresses.
In 2007, a new open flame mattress standard (16 CFR Part 1633 Standard for the Flammability (Open Flame) of Mattress Set3)
went into effect requiring all manufactured, imported or renovated
mattresses to meet this standard. In 2008, the CPSC released a Notice of
Proposed Rulemaking: CPSC NPR 16 CFR Part 1634 Standard for the Flammability of Residential Upholstered Furniture.4 Currently, it is not clear if this proposed standard for upholstered furniture will be adopted by the CPSC.
There has been significant opposition to the standard from the
California Bureau of Home Furnishings Insulation and the National
Association of State Fire Marshals and several other interested parties.
Most of the comments, from outside the furniture industry, are critical
of the standard, believing that it is not stringent enough to be
effective at reducing the death toll from furniture fires. The public
comments on the proposed standard can be found on the CPSC website: http://www.cpsc.gov/LIBRARY/FOIA/FOIA08/pubcom/flamm1.pdf.
Complex Behavior of Upholstered Furniture5
The complex nature of upholstered furniture fires is well known, and
the melting behavior of polyurethane foam and synthetic fabrics is
obvious in furniture fires, yet the detailed modeling of such phenomena
is still very much in its infancy. After flaming ignition has occurred,
the general burning behavior of an upholstered furniture item, ignited
on the seat, can be broken down into four main phases: spread; burn
through; pool fire; and burn out. Figure 1 shows the mass and heat
release rate histories for a chair with polyurethane foam covered by
wool fabric. The four phases of burning have been highlighted on the
plot. The spread phase covers from ignition until the entire seat, back,
and arms are burning. This can be seen in the early stages of the fire
where the heat release rate is steadily growing.
Once the fire has spread over the surface, the fire enters a burn
through phase marked by a quasi-steady heat release rate as the fire
burns through the seat cushion. Once the seat burns through, the melted
fuel will spill onto the floor marking the pool fire phase which is seen
as a rapid increase in the heat release rate. This is typically the
time of maximum heat release rate.
After most of the melted fuel is consumed, the fire enters the burn
out phase where the heat release rate declines and the frame of the item
continues to burn at a reduced rate. When a thermo plastic fabric is
used, the burn through phase can be almost nonexistent, resulting in an
extremely rapid growth to the maximum heat release rate.
Figure 1. Mass loss and heat release rate
histories for a single seat upholstered chair with wool fabric covering
Modeling the Combustion of Upholstered Furniture
The fabrics used, liners, foam chemistry and fire retardants combine to
create a complex burning behavior. All of this makes the modeling of
upholstered furniture extremely challenging.
The importance of the migration of the melted fuel to the floor
cannot be overstated. Figure 2 shows the computer predictions from the
Fire Dynamics Simulator version 5 (FDS5) for an upholstered chair
compared with the experimental results. The computer animation of the
burning chair is shown in the upper corner of Figure 2.
The results show good agreement during the quasi-steady burning
phase, but the model over-predicts the growth rate during the first 100
seconds. The model is not able to capture the rapid fire growth that
occurs around 200 seconds that results from the spilling of the melted
fuel onto the floor from the seat area. The migration of fuel is not
included within FDS5, and current efforts to model upholstered furniture
in FDS5 have had only limited success due to the limitations of the
physics of the model. The result is that the predictive capability for
the heat release rate is not sufficiently accurate for many engineering
Figure 2 – Fire Dynamic Simulator (FDS5) prediction compared with experimental results for an upholstered chair.
More complex models that predict the melting behavior of thermo
plastic materials are being developed using specific finite element
codes in two-dimensions that require significant computer resources to
model the melting behavior.6
As of yet, these models do not include the combustion the flammable
gases that are released, and they only model simple geometries.
Unfortunately it will be a number of years before accurate predictive
models that incorporate melting fuel transport are available for
engineering design applications. In the mean time, fire protection
engineers must rely on experimental results and correlations, rather
than models when evaluating upholstered furniture.
Babrauskas, V., "Upholstered Furniture and Mattresses", Fire Protection Handbook, 18th Ed, National Fire Protection Association, Quincy, Massachusetts, 2002.
Sundstrom, B. (Ed.) CBUF: Fire safety of upholstered furniture - the
final report on the CBUF research program. Director-General Science,
Research and Development (Measurements and Testing). European
Commission. Report EUR 16477 EN, 1995.
16 CFR Part 1633 Standard for the Flammability (Open Flame) of Mattress Sets; Final Rule, Consumer Product Safety Commission, 15 March 2006.
16 CFR Part 1634 Standard for the Flammability of Residential Upholstered Furniture, Consumer Product Safety Commission, 4 March 2008.
Fleischmann, C. and Hill G., "Burning Behaviour of Upholstered Furniture," Interflam '04, Interscience Communications Co., London, 2004.
Butler, K. "A Model of Melting and Dripping Thermoplastic Objects in Fire", Proceedings of the Fire and Materials - 11th International Conference, Interscience Communications Co.,
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