Heat release rate ignition

The flammability of solids may be considered to be a function of the heat release rate and critical ignition energy of the material being studied. Flammability is an inverse function of the actual ignition energy of the material in question, and it is directly related to the rate of heat liberated after ignition of the sample. 

Figure 2. The Radiant Panel Test was designed to measure both critical ignition energy and rate of heat release. A sample is mounted facing a controlled heat flux but at a 3CP angle to it such that the upper part of the specimen is more severely exposed. Since irradiance decreases down the specimen, the time progress of ignition down the specimen serves to measure central ignition energy. Thermocouples in the stack above the specimen serve as a measure of heat release rate.

Total Heat Release From Wall Assemblies. We examined the total heat release from the wall assemblies as total heat contribution. The total heat release is obtained by integrating the area under the heat release rate curve with time and it is expressed in megajoules (MJ). The total heat release data from ignition to different times are shown in Table III for the wall assemblies. 

Comparison of Study to Previous Work. The only work that can be compared to ours is that of Brenden and Chamberlain (6) using the same furnace and Chamberlain and King (7) using a different furnace. The assemblies used in these studies were of similar construction. The wall assemblies used contained fire-retardant-treated studs as the only combustibles. The interior and exterior sides were 5/8-in. (16-mm) type-X gypsum. Thus, heat release rates were understandably small. The onset of heat release started at 23 min after ignition. After that, a slow increase occurred, culminating to approximately 100 Btu/min ft2 (19 kW/m2) at 60 min. For an exposed area of 8 by 10 ft (2.44 by 3.05 mm), this would be 140 kW. 

Fire hazard is a combination of several properties, including ignitability, flammability, flame spread, amount of heat released, rate of heat release, smoke obscuration and smoke toxicity. 

Fire safety in a particular scenario is improved by decreasing the corresponding level of fire risk or of fire hazard. Technical studies will, more commonly, address fire hazard assessment. Fire hazard is the result of a combination of several fire properties, including ignitability, flammability, flame spread, amount of heat released, rate of heat release, smoke obscuration and smoke toxicity. 

Standard Method of Test for Heat Release Rates for Upholstered Furniture Components or Composites and Mattresses Using an Oxygen Consumption Calorimeter, 1990. Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source, 1994. 

Taffanel used measurements of the chemical reaction rate at temperatures lower than the temperature of self-ignition, and measurements of the time of self-ignition at a higher temperature, in order to determine the dependence of the heat release rate on the temperature and concentration. Further, Taffanel introduced measurements of the flame propagation velocity. He compared experimental data with the theoretical calculation, carried out under the assumptions of a constant chemical reaction rate in the interval from Tb to Tb — 9 and the absence of chemical reaction at all lower temperatures, also ignoring the Arrhenius dependence of the reaction rate on the temperature and the variation of the concentration. 

Taffanel s indisputable achievement is his statement of the problem of flame velocity in a mixture characterized by a specific smooth dependence of the reaction rate on the temperature, whereas many authors, both before and after Taffanel, based their calculations on the concept of an ignition temperature at which there was supposedly a jump in the reaction rate. This achievement is a consequence of the theory of self-ignition which Taffanel developed in which the temperature of ignition depends on the interrelation between the continuously varying heat release rate and the conditions of heat transfer. 

Heat release rate is another relevant measure of the combustibility of a material along with ease of ignition and flame spread. Smith (55) points out that the release rate data, obtained under different test exposures, will be useful in predicting the performance in actual fires under different fuel loading. Release rate data can thus be used—along with other... 

Note TTI, time to ignition PHRR, peak of heat release rate MAHRE, maximum average rate of heat emission THR, total heat release EHC, effective heat of combusion TSR, total smoke released. 

Note rign = time to ignition, PHRR = peak of heat release rate, THR = total heat release, AMLR = average mass loss rate, ASEA = average specific extinction area. 

A furniture calorimeter consists of a weighing platform that is located on the floor of the laboratory, beneath a hood connected to an instrumented exhaust duct (see Figure 14.13). The object is placed on the platform and ignited with the specified ignition source. The products of combustion are collected in the hood and extracted through the exhaust duct. Measurements of oxygen concentration, flow rate, and light transmission in the exhaust duct are used to determine the heat release rate and smoke production rate from the object as a function of time. 

Smith, E., Heat release rate of building materials. In Ignition, Heat Release and Noncombustibility of Materials, ASTM STP 502, American Society of Testing and Materials, Philadelphia, PA October 6, 1971, Washington, DC, 1972, pp. 119-134. 

Requirements for upholstered furniture flammability exist in various states, including California, based on California Technical Bulletin 133 (CA TB 133),91 which was also made into a consensus standard by ASTM committee E05 as ASTM E 1537.92 The gas burner used as the ignition source in CA TB 133 is a square-shaped burner that applies propane gas for 80s at a flow rate of 13L/min. The test is severe enough that it can usually not be met, unless the foam contained in the upholstered furniture item is flame-retarded. The pass/fail criteria are a peak heat release rate of 80 kW and a total heat released that does not exceed 25 MJ over the first 10 min of the test. In California, moreover, all foam contained within upholstered furniture must be flame-retarded to comply with CA TB 117. Moreover, the IFC and NFPA 101 both have parallel requirements to those discussed earlier for mattresses. In other words, the 2006 editions of both the codes contain requirements that upholstered furniture items in health care occupancies as well as detention and correctional occupancies that are not sprinklered must comply with a peak heat release rate of 250kW and a total heat release of no more than 40 MJ in the first 5 min of the test, when tested to ASTM E 1537 (or CA TB 133). However, the 2007 edition of the IFC and the 2009 edition of NFPA 101 lowered these values to 80 kW and 25 MJ over 10 min. Finally, the IFC 2007 added college and university dormitories to the list and eliminated the sprinkler exception for detention occupancies. 

In recent years, a new fire-test instrument was developed the pyrolysis combustion flow calorimeter (PCFC) or microcalorimeter.209 210 This instrument (Figure 21.17) was developed by Richard Lyon and his coworkers at the FAA laboratories. It enables the determination of parameters such as specific heat release rate (W/g), heat of combustion (J/g), and ignition temperature (°K), to be quickly determined from very small (1-50 mg) test specimens. The technique has been standardized by ASTM as ASTM D 7309. Data from the PCFC has been shown to be capable of being correlated... 

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