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|Evaluating the Fire Threat from Upholstered Furniture|
Issue 39: Evaluating the Fire Threat from Upholstered Furniture
By Charles Fleischmann, Ph.D., P.E.
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
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.
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 designs.
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.
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