Objective - To develop the measurement science and technology that reduces losses outside the room of fire origin (flashover) due to fires involving soft furnishings. This will be accomplished by 1) validating the use of NIST backcoating technology in real-scale mockups, 2) developing bench scale tools to predict the effectiveness of fire-blocking barriers in reducing the heat release rate of RUF items, 3) providing quantitative guidelines to identify minimum heat release rate upholstery combinations in furniture design, and 4) providing robust reference materials and standard methods for smoldering ignition testing.
What is the new technical idea? The burning behavior of RUF is widely recognized as a dominant factor in the ignition, spread, and growth of building fires, particularly residential fires, which account for 80 % of fire deaths and property losses. Recent data from NFPA indicate an increasing trend in deaths for fires involving RUF since 2011 and reinforce the need for a national fire regulation.
The findings of a recent NIST workshop (August 2016) confirmed the important role of flaming residential upholstered furniture in fire losses, and identified improving RUF burning behavior as the top priority application for fire loss reduction. An analysis performed by John Hall of NFPA as a direct result of a previous NIST workshop provided the first quantitative estimate for the role of flaming RUF in fire losses when RUF is not the first item ignited. More recent work using a novel statistical analysis addressed this issue. Significantly, flaming fires (both as first and later item ignited) are estimated to be responsible for roughly half (a much higher fraction than previously estimated) of the deaths as those due to fires in which RUF is directly ignited by smoldering sources. This estimate, when combined with the NIST workshop conclusion that the vast majority of fire losses associated with RUF fires started by smoldering ignition occur after transition to flaming, confirms that the flaming burning behavior of RUF is the dominant factor in fire losses associated with RUF burning. Most prior attempts to curb the contribution of RUF to fire losses have consisted of limiting ignition, primarily smoldering ignition. As a result of concerns about the toxicity of flame retardants currently used in RUF, the only RUF fire standard in the United States (California Technical Bulletin 1172000), that addressed the resistance of RUF soft fillings to small-flame ignition, was amended to only consider the likelihood of smoldering ignition of filling materials by the covering upholstery fabric when exposed to a smoldering standard cigarette (California TB 117 2013).
Due to the central role flaming RUF plays in fire losses, this project is focused on providing the understanding and tools required to reduce the ignition, growth rate, and heat release rate of these flaming fires.
Routine fire testing of full-scale RUF is impractical due to the large numbers and wide ranges of styles and materials, the rapid, fashion driven changes in upholstery materials, the relatively small numbers of a given RUF design and material combination that are generally produced, the high cost of testing, the time delay in obtaining test results once the customer has “designed” their RUF, and the shortage of capable test facilities.
The development of a technically sound furniture design tool based on characterized physical and combustion properties of the furniture components will be required by furniture manufacturers to produce RUF meeting potential future regulations based on limiting the heat release rate of RUF. Such a design tool will enable RUF manufacturers to identify the materials and configurations necessary to produce furniture with desired levels of fire performance. By designing furniture that is unlikely to generate sufficient heat release rate to initiate flashover in a room, the likelihood of flashover, with its associated fire losses, in residences will be substantially reduced.
Fire blocking barrier fabrics (BFs) appear to be the most promising technology for compliance with any future proposed flaming RUF regulation while satisfying environmental, health, and safety (EHS) concerns (currently a major public focus) as the performance of some BFs do not require the use of fire retardants. We will develop the measurement science that enables selection and standardized testing of barrier fabrics (BF) for use in RUF. Currently, there is no bench-scale test capable of assessing the effectiveness of fire-blocking barriers on RUF flammability. We will develop capabilities to understand the mechanism of actions of fire-blocking materials on RUF flammability and design a measurement tool capable of capturing these mechanisms. During the current phase a small-scale heat release test will be developed and tested as a means for evaluating the effectiveness of fire-blocking barriers in RUF mockups.
NIST is also working to develop material flammability technologies that can decrease the heat release rate of RUF with EHS-compliant solutions. In FY17 EL’s Fire Research Division has continued development of a Patent Pending technology based on a backcoating (i.e., coating applied to the unexposed side of a fabric) formulation (http://patents.com/us-20160362563.html). This technology has the potential to substantially decrease the fire hazard of RUF by fully suppressing smoldering cigarette ignition, by delaying flaming ignition, and by decreasing the burning rate of RUF. These results have been demonstrated with small scale tests. Additional tests will be run in FY17 on real scale to demonstrate the effectiveness of this approach.
Studies are continuing with the goal of developing the measurement science necessary to provide a small-scale smoldering test capable of better differentiation between materials being tested (cover fabrics, barrier fabrics, or cushioning), providing improved reliability and reproducibility, and having a demonstrated correlation with observed smoldering behaviors on real-scale mock-ups and actual furniture. In FY17 NIST submitted suggested modifications to the National Fire Protection Agency (NFPA) for updating the existing smoldering standard, NFPA 260. The suggestions included modifications to pass/fail criteria, sample holder, sample size and testing conditions. As a result, workgroups have been created by NFPA to consider inclusion of these modifications in NFPA 260. Significantly, ASTM is considering similar changes for their smoldering ignition standard, ASTM E13-53. In FY18 we will provide additional experimental data to further support the efforts of testing agencies.
NIST will continue providing robust reference materials and standard methods for smoldering ignition testing. Changes in the manufacture of the filter paper used to determine the ignition propensity of cigarettes have potentially weakened the effectiveness of the fire safety regulations. In response, NIST has carried out a study to identify a new substrate. During Phase 1, NIST developed a new substrate that captures the performance of the original substrate. A round robin study designed to assess how well the modified approach matches results from the original standard and its reproducibility was completed during the third year. The findings of this study, along with ballot text to affect the change in substrate, were shared with ASTM E05.15, the subcommittee responsible for maintaining this standard. While an Interlaboratory Study (ILS) of the current steel-based substrate was underway, an outside laboratory examined a circular, but otherwise equivalent version. The round substrate is easier to use and requires minimal modification of the ASTM E 2187 apparatus, as compared to the rectangular version. In FY18 we will organize a second ILS to support the replacement of the rectangular substrate with the circular steel substrate.
Supplies of the current SRM 1082 (reduced ignition propensity) and SRM 1196 (standard ignition propensity) cigarettes will be maintained by procuring and certifying new batches. SRM 1082 will be recertified by the end of FY17 to provide a supply of SRM 1082 that will last for 6-7 years. SRM 1196 cigarettes are the only ones that assuredly meet the ignition source requirements in ASTM, NFPA, CPSC, and California standards for determining the cigarette ignition resistance of upholstered furniture and mattresses. At the present sales rate, there is an approximately 18-month supply of SRM 1196 cigarettes. In FY17 the contract for manufacturing the cigarettes will be awarded and in FY18 a new batch of SRM 1196 will be certified.
NIST will continue supporting the regulators by providing the technical basis for developing smoldering ignitions bench-scale tests with improved real-scale correlation and reproducibility.
Smoldering propensity of flexible polyurethane foam can dramatically vary between different foam batches or even between different locations in the same foam batch. This variability in foam smoldering propensity affects the classification of upholstery fabrics in standard tests that rely on a foam substrate. During FY 15, NIST showed that surface area and air permeability of the foam plays a key role on its smoldering propensity. In FY 17 we observed that batch-to-batch variations in foam properties significantly affected the smoldering propensity of the flexible polyurethane foam used in Cal 117-2013. In FY18 we will use reticulation, a foam post-process that removes residual foam membranes, to decrease variations in surface area and air permeability of the foam and thereby promote a more reproducible smoldering behaviour of the foam. If reticulated Cal TB 117-2013 compliant foam shows a significant improvement in smoldering repeatability as compared to the pristine foam, then such a reticulated foam will be proposed as a standard foam for use in smoldering RUF tests.
This project is in direct alignment with the strategic roadmap on innovative fire protection.
What is the research plan? This is the third year of Phase 2 for this project. The landscape for the project has changed dramatically since its inception as discussed above. Recent workshops and conferences have highlighted these issues. This public focus on RUF has vastly increased the immediate need for NIST findings as well as raising the visibility and scrutiny of our efforts.
The public discussion, workshops, and individual discussions with workshop attendees from government and the private sector highlighted areas where additional research is required and provided an important opportunity to reassess our working hypotheses and research plans. While leading us to slightly modify our research focus, we have concluded that our current research directions are well matched to and appropriate for the rapidly changing regulatory and public perception environments.
The research effort for FY 18 and beyond is broken into a number of Tasks.
We will validate the use of NIST backcoating technology with real-scale mockups. Four upholstered cushions will be mocked up in chair configurations with Cal 117-2013 foam. Upholstery fabrics will be sewed using fire resistant aramid thread. In the previous phase of this project, zippers have been identified as a weak point in terms of fire performance of fire barriers, thus, no zipper will be used.
We will design a bench-scale test to measure the heat release rate of RUF mockups in the presence of fire-blocking barriers. The new bench scale test will lead to better understanding of the mechanisms by which fire-blocking materials improve RUF flammability by providing a measurement tool capable ideintifying and quantifying these mechanisms. The basic assumption is that the largest fuel source in RUF is the filling material (generally polyurethane foam) and fire-blocking barriers can significantly reduce the heat release rate of RUF by reducing heat and mass transfer through the fire-blocking barrier. Heat transfer through the fire-blocking barrier controls the rate at which combustible gases of pyrolysis are generated via thermal decomposition of the foam. Mass transfer through the fire-blocking barrier controls the rate at which the combustible gases of pyrolysis are released into the flame.
The test developed in this task will capture the effect of the fire-blocking barrier on mass and heat transfer. This implies that the fire-blocking barrier in the mockup will be sealed around the filling material to fully capture the effect of a fire-blocking barrier on mass transfer. A sample holder will be designed to allow a reliable and convenient sealing of the fire-blocking barrier around the filling material. The failure of the fire-blocking barrier (i.e., loss of mechanical integrity and fire burn-through) can obviously affect mass/heat transfer through the fire-blocking barrier. The sample holder will be designed to capture possible failure mechanisms of the fire-blocking barriers, like pressure build-up for non-permeable barriers and stress induced by barrier fabric shrinkage.
In this task, we will determine whether the bench-scale described in Task 2 can be used to provide quantitative guidelines to identify minimum heat release rate upholstery combinations in furniture design. In particular, we will determine whether the bench-scale test can be used to identify those upholstery combinations which contain the heat release rate below approximately 500 kW in real scale mockups. Our previous findings show that room-flash over is extremely unlikely for heat release rate values below 500 kW.
Real-scale mockups are chosen for initial demonstration in order to limit the wide range of geometric and material effects expected for actual RUF. Four upholstered cushions will be mocked up in chair configurations with Cal 117-2013 foam. Upholstery fabrics will be sewed using fire resistant aramid thread. Cushions will be produced from a variety of commonly used barrier fabrics, polyester fiber fill, and cover fabrics chosen to span a wide range of flammability properties.
In this task, we will use our improved understanding of smoldering behavior as the basis for suggesting possible changes to the decades-old standard fabric test used for smoldering RUF regulations with the goal of providing improved material property differentiation and reproducibility with a test that correlates with smoldering behavior on real-scale upholstery.
We will investigate the effect of reticulation on the smoldering propensity of flexible polyurethane foams. Our hypothesis is that reticulation will improve the smoldering reproducibility of fabric-covered flexible polyurethane foam. The validity of this hypothesis will be investigated by measuring smoldering propensity of mock-ups with polyurethane foam that complies with the California standard TB117-2013. The smoldering ignition propensity of Cal TB117-2013 compliant foams will be measured before and after reticulation. Three different foam batches will be used to evaluate the impact of reticulation on batch-to-batch smoldering reproducibility.
NIST will also continue providing robust reference materials and standard methods for smoldering ignition testing. Supplies of the current SRM 1082 (reduced ignition propensity) and SRM 1196 (standard ignition propensity) cigarettes will be maintained by procuring and certifying new batches.