Study of critical velocity and backlayering length in longitudinally ventilated tunnel fires

The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

Model scale tunnel fire tests with longitudinal ventilation

Intuitively, the rate of heat release from an unwanted fire is a major indication of the threat of the fire to life and property. This is indeed true, and a reliable measurement of a fire’s heat release rate was a goal of fire researchers at NBS and other fire laboratories at least as early as the 1960s. Historically, heat release measurements of burning materials were based on the temperature rise of ambient air as it passed over the burning object. Because the fraction of heat released by radiant emission varies with the type of material being burned, and because not all the radiant energy contributes to temperature rise of the air, there were large errors in the measurements. Attempts to account for the heat that was not captured by the air required siting numerous thermal sensors about the fire to intercept and detect the additional heat. This approach proved to be tedious, expensive, and susceptible to large errors, particularly when the burning “object” was large, such as a full-sized room filled with flammable furnishings and surface finishes. A novel alternative technique for determining heat release rate was developed at NBS during the 1970s. It had distinct advantages over the customary approach, but its widespread acceptance was hampered by uneasiness in the fire science community concerning potential errors if the technique were used in less-than-ideal circumstances. In 1980 Clayton Huggett, a fire scientist at NBS, published the seminal paper [1] that convinced the fire science community that the new technique was scientifically sound and sufficiently accurate for fire research and testing. The technique is now used worldwide and forms the basis for several national and international standards. The underlying principle of the new heat release rate technique was “discovered” in the early 1970s. Faced with the challenge of measuring the heat release of combustible wall linings during full-scale room fire tests, William Parker, Huggett’s colleague at NBS, investigated an alternative approach based on a simple fact of physics: in addition to the release of heat, the combustion process consumes oxygen. As part of his work on the ASTM E 84 tunnel test, Parker [2] explored the possibility of using a measurement of the reduction of oxygen in fire exhaust gases as an indicator of the amount of heat released by the burning test specimens. Indeed, for well-defined materials with known chemical composition, heat release and oxygen consumption can both be calculated from thermodynamic data. The problem with applying this approach to fires is that in most cases the chemical compositions of modern materials/ composites/mixes that are likely to be involved in real fires are not known. In the process of examining data for complete combustion (combustion under stoichiometric or excess air conditions) of the polymeric materials with which he was working, Parker found that, although the heat released per unit mass of material consumed (i.e., the specific heat of combustion), varied greatly, the amount of heat released per unit volume of oxygen consumed was fairly constant, i.e., within 15 % of the value for methane, 16.4 MJ/m of oxygen consumed. This fortunate circumstance—that the heat release rate per unit volume of oxygen consumed is approximately the same for a range of materials used to construct buildings and furnishings—meant that the heat release rate of materials commonly found in fires could be estimated by capturing all of the products of combustion in an exhaust hood and measuring the flow rate of oxygen in that exhaust flow. The technique was dubbed oxygen consumption calorimetry, notwithstanding the absence of any actual calorimetric (heat) measurements. Later in the decade, Huggett [1] performed a detailed analysis of the critical assumption of constant proportionality of oxygen consumption to heat release. Parker’s assumption was based on enthalpy calculations for the complete combustion of chemical compounds to carbon dioxide, water, and other fully oxidized compounds. Indeed, a literature review by Huggett revealed that Parker’s findings were actually a rediscovery and extension of the work of W. M. Thornton [3], published in 1917, which found that the heat released per unit amount of oxygen consumed during the complete combustion of a large number of organic gases and liquids was fairly constant. Nevertheless, since in real fires and fire experiments the oxygen supply is sometimes limited, incomplete combustion and partially oxidized products can be produced. Huggett’s paper examined in detail the assumption of constant heat release per amount of oxygen consumed under real fire conditions and assessed its effect on the accuracy of heat release rate determinations for fires. Instead of expressing results on a unit volume basis, as Parker did, Huggett expressed results in the more convenient and less ambiguous unit mass of oxygen

Estimation of Rate of Heat Release by Means of Oxygen Consumption Measurements

EFSA was asked by the European Commission to deliver a scientific opinion on polybrominated diphenyl ethers (PBDEs) in food. PBDEs are additive flame retardants which are applied in plastics, textiles, electronic castings and circuitry. PBDEs are ubiquitously present in the environment and likewise in biota and in food and feed. Data from the analysis of 19 PBDE congeners in 3,971 food samples were provided to EFSA by 11 European countries. Eight congeners were considered by the Panel on Contaminants in the Food Chain (CONTAM Panel) to be of primary interest: BDE-28, -47, -99, -100, -153, -154, -183 and -209. The highest dietary exposure is to BDE-47 and -209. Toxicity studies were carried out with technical PBDE mixtures or individual congeners. Main targets were the liver, thyroid hormone homeostasis and the reproductive and nervous system. PBDEs cause DNA damage through the induction of reactive oxygen species. The Panel identified effects on neurodevelopment as the critical endpoint, and derived benchmark doses (BMDs) and their corresponding lower 95 % confidence limit for a benchmark response of 10 %, BMDL10s, for a number of PBDE congeners: BDE-47, 309 μg/kg b.w.; BDE-99, 12 μg/kg b.w.; BDE-153, 83 μg/kg b.w.; BDE-209, 1,700 μg/kg b.w. Due to the limitations and uncertainties in the current database, the Panel concluded that it was inappropriate to use these BMDLs to establish health based guidance values, and instead used a margin of exposure (MOE) approach for the health risk assessment. Since elimination characteristics of PBDE congeners in animals and humans differ considerably, the Panel used the body burden as starting point for the MOE approach. The CONTAM Panel concluded that for BDE-47, -153 and -209 current dietary exposure in the EU does not raise a health concern. For BDE-99 there is a potential health concern with respect to current dietary exposure. © European Food Safety Authority, 2011 1 On request from the European Commission, Question No EFSA-Q-2009-00684, adopted on 9 May 2011. 2 Panel members: Jan Alexander, Diane Benford, Alan Raymond Boobis, Sandra Ceccatelli, Bruce Cottrill, Jean-Pierre Cravedi, Alessandro Di Domenico, Daniel Doerge, Eugenia Dogliotti, Lutz Edler, Peter Farmer, Metka Filipic, Johanna Fink-Gremmels, Peter Furst, Thierry Guerin, Helle Katrine Knutsen, Miroslav Machala, Antonio Mutti, Martin Rose, Josef Rudolf Schlatter and Rolaf van Leeuwen. Correspondence: contam@efsa.europa.eu 3 Acknowledgement: The Panel wishes to thank the members of the Working Group on Brominated Flame Retardants in Food: Ake Bergman, Alan Raymond Boobis, Sandra Ceccatelli, Jean-Pierre Cravedi, Metka Filipic, Peter Furst, Niklas Johansson, Helle Knutsen, Miroslav Machala, Franco Merletti, Olaf Papke, Dieter Schrenk, Rolaf van Leeuwen, Stefan van Leeuwen and Marco Zeilmaker for the preparatory work on this scientific opinion and the hearing experts: Bas Bokkers and Catherine Viguie, and EFSA staff: Alessandro Carletti, Gina Cioacata, Luisa Ramos Bordajandi and Elena Scaravelli for the support provided to this scientific opinion. The CONTAM Panel acknowledges all the European countries that provided PBDEs occurrence data in food and supported the consumption data collection for the Comprehensive European Food Consumption Database. 4 The term “intra-species” has been replaced by “inter-species” in the Summary and in Chapter 9.1.

https://www.cancer-environnement.fr/Portals/0/Documents%20PDF/EFSA,%202011.pdf

Scientific Opinion on Polybrominated Diphenyl Ethers (PBDEs) in Food

Introduction.- Fuel and ventilation controlled fires.- Tunnel fire tests.- Heat release rates in tunnels.- Fire growth rates in tunnels.- Design fire curves.- Combustion products from fires.- Gas temperatures.- Flame length.- Heat flux and thermal resistance.- Fire spread.- Smoke stratification.- Tunnel fire ventilation.- Visibility.- Tenability.- Fire suppression and detection in tunnels.- CFD modeling of tunnel fires.- Scaling technique.

Tunnel Fire Dynamics

Heat release rates from heavy goods vehicle trailer fires in tunnels

Gas temperatures in heavy goods vehicle fires in tunnels

Runehamar tunnel fire tests

An analysis of fire spread during four large-scale fire tests that were performed in the Runehamar tunnel in Norway is presented. The fire loads consisted of mock-ups simulating a Heavy Goods Vehicle (HGV) trailer. The fire spread downstream of the HGV trailer mock-ups was studied, both to large targets with the same type of commodities as used in the trailer mock-up for each tests, and to small pieces of wood and plastic poles placed at different distances from the fire. The purpose was to determine a critical distance for fire spread between HGV trailers for different heat release rate histories. The time to ignition of a second object and fire spreading distances were estimated from post-visual observations and temperature measurements. Correlations for flame length were developed from the experimental results. Since the average temperature of the cross-section often is used to estimate fire spread, results from a model for the average temperature were compared with the measured temperatures.

Anders Lönnermark

Papers

Tunnel Fire Dynamics

Heat release rates from heavy goods vehicle trailer fires in tunnels

Gas temperatures in heavy goods vehicle fires in tunnels

Runehamar tunnel fire tests

Fire Spread and Flame Length in Large-Scale Tunnel Fires