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

Heat release rates of burning gasoline and wood fires in a room were studied by computational fluid dynamics (CFD). Version 5.5.3 of the software Fire Dynamics Simulator (FDS), which is the latest one available, was selected as the CFD simulation tool. Predicted results were compared with two sets of reported data from full-scale burning tests. In the two sets of experiments, the scenarios were set at gasoline pool fire and wood chipboard fire with gasoline respectively. The input heating rate of gasoline pool fire based on experimental measurements was used in the first set of experiments. Three scenarios G1, G2 and G3 with different grid systems were simulated by CFD. The grid system of scenario G2 gave more accurate prediction, which was then used to study the second set of experiments on wood chipboard with gasoline. The combustion model in FDS was used in wood chipboard fire induced by gasoline pool. The wood chipboard was allowed to burn by itself using the pyrolysis model in FDS. The effects of the boundary conditions on free openings for the same set of experiments were studied by three scenarios SOB1, SOB2 and SOB3. Boundary condition SOB2 gave more reliable prediction among the three boundary conditions. Two other scenarios on the effect of moisture content of wood were also studied. The predicted HRR curve was found to agree better with experiment in using SOB2.

Numerical studies on heat release rate in a room fire burning wood and liquid fuel

Performance evaluation of water mist with bromofluoropropene in suppressing gasoline pool fires

The new version of the fire dynamics simulator, FDS version 3.01, is verified by a series of full-scale fire tests. Experiments are carried out in a compartment similar in size to the ISO-9705 room calorimeter. Gasoline pool fires of different diameters are used to give different heat release rates. The ventilation factors of the compartment are adjusted to produce flashover. Fire-induced flow, temperature, and pressure fields in these different physical scenarios are calculated using the FDS software. The predictions for temperature and radiative heat flux of a post-flashover fire in the specific configuration tested are in reasonably good agreement with experimental results even when the flame occupies most of the room volume.

Evaluation of the Field Model, Fire Dynamics Simulator, for a Specific Experimental Scenario:

Application of water@silica core-shell particles for suppressing gasoline pool fires.

Local professionals are quite worrying about whether a water mist fire suppression system (WMFSS) can extinguish afire rapidly. It was also suggested in the literature that discharging water mist, even under the design operating conditions, might not always control afire rapidly. To explore more on that, a series of experiments on discharging water mist from low/moderate-pressure system on gasoline fires were carried out at the new full-scale burning facility, Poly U/USTC Assembly Calorimeter at Lanxi, Harbin, Heilongjiang China. An interesting point identified for quick communication is that for some designs of fuel container, the liquid fire cannot be extinguished even when all the fuels were consumed.

Will Water Mist Extinguish a Liquid Fire Rapidly

Studies on minimum beat release rates for flashover in a compartment fire will be reported in this paper. Experiments were carried out in a chamber with dimensions similar to that in the standard ISO9705 Room-Corner Fire test. This chamber is located inside a new full-scale burning facility, the PolyU/HEU Assembly Calorimeter, at the remote areas of Northern China. This is a joint project between Department of Building Services Engineering, The Hong Kong Polytechnic University (PolyU) and the Harbin Engineering University (HEU) in Heilongjiang, China. Heat release rates were measured by the oxygen consumption method. Correlation equations on estimating the minimum heat release rates for flashover will be reviewed and compared with the experimental results. Results are useful in fire hazard assessment while implementing engineering performance-based codes.

Experimental Studies on Minimum Heat Release Rates for Flashover with Oxygen Consumption Calorimetry

With the increasing integration of distributed energy resources and DC loads, DC distribution system is a new development direction of urban distribution network in the future. Recently, a lot of research has been done on DC network and its potential for sustainable and fast evolving cities. Inspire of the advantages as well known, this paper presents the construction of DC distribution system in China beginning with the analysis of demonstration projects. The main challenges of promoting DC network in planing and development of smart cities are proposed. Key technologies to realize construction are summarized. Finally, future research tasks and construction suggestions are proposed according to technique, equipment and project. 

H. Dong

Papers

Will Water Mist Extinguish a Liquid Fire Rapidly

Experimental Studies on Minimum Heat Release Rates for Flashover with Oxygen Consumption Calorimetry

Construction of DC distribution system in smart city : challenges and suggestions