Fire growth heat release rate

The surface burning characteristics (flame spread index and smoke developed index) for wood and wood products as measured by American Society for Testing and Materials (44) can be reduced with fire retardant treatments, either chemical impregnation or coatings (48). Fire retardant treatments also reduce the heat release rate of a burning piece of wood (49,50). The heat release rates (51) of the burning materials are an important factor in fire growth. 

MAKEFIRE models the growth, steady state, and decay phases of the each fuel element in the compartment. It consists of routines that create and edit fire files that specify the fire heat release rate and fuel pyrolysis rate as a function of time. 

FIGRA index (fire growth rate index) defined as the peak heat release rate in kW during the period from ignition to flashover (excluding the contribution from the ignition source) divided by the time at which the peak occurs (kW/s) ... 

Time to ignition Peak heat release rate Time to peak heat release Total heat release Peak smoke production rate Time to peak smoke production Total smoke production Fire growth rate index (FIGRA)... 

FIGRA is now believed to be one of the most relevant parameters and is related to the size and growth rate of a fire. FIGRA is calculated from the peak heat release rate divided by the time to peak. Similarly, SMOGRA is the peak smoke production rate divided by the time to peak. 

The convective heat release rates for each commodity are shown in Fig. 3.3. As seen in this figure, each commodity exhibited a similar initial fire growth as the... 

Enclosed fires may exhibit fire growth characteristics as shown in Figure 5-5. Unlike gaseous or liquid fuels, there may be a considerable fire growth period in which temperatures and overall heat release is low and the fire is localized. As the fire becomes fully developed, the entire room volume can become engulfed in flames, finally, as air is depleted or fuel is consumed, a decay period occurs. In many cases, an enclosure fire will be starved for air ("ventilation-limited"), and the available airflow becomes the limiting factor for the fuelburning rate. 

The rate at which heat is released in a compartment is the most important factor affecting fire growth toward flashover and the severity of subsequent post-flashover fire conditions. This can be illustrated as follows ... 

Of the several approaches that have been used to calculate fuel generation rates from solid materials in CFD-based fire growth calculations, the simplest are empirical models. Instead of attempting to model the physical processes that lead to gaseous fuel production inside decomposing solids, empirical data that can be measured (transient heat release or mass loss rate) or inferred (heat of gasification) from common bench-scale fire tests such as the Cone Calorimeter are used to characterize fuel generation processes. 

FIGRA, fire growth rate THR600s, total heat release LFS, lateral flame spread SMOGRA, smoke growth rate TSP600s, total smoke production F flame spread FIPEC, Fire Performance of Electric Cables (Reference 105). 

One of the most important parameters that can be nsed to characterise a fire is the rate of heat release. It provides an indication of the size of the fire, the rate of fire growth and consequently the release of smoke and toxic gases, the time available for escape or suppression, the type of snppressive action that are likely to be effective and other attributes that define the fire hazard. Methods based on the oxygen consumption principle are now available to measnre the rate of heat release reliably and accurately. The principle depends upon the fact that the heats of combustion of organic materials per unit of oxygen consumed are approximately the same. This is because the processes in the combustion of all these prodncts involve the breaking of C-C and C-H bonds (which release approximately the same amonnt of energy) with the formation of CO2 and water. 

Basically the test involves mounting a corner section specimen - a vertical 1.5 m high by 1.0 m wide panel and another 1.5 m by 0.5 m at 90 degrees - under an enclosed calorimeter bood. Tbe Fire Research Station says the setup can accurately measure the rate of heat release, considered one of the most important parameters in assessing fire growth, also time to ignition, rate of lateral flame spread, time of production of flaming droplets and rate of smoke release. 

FIGRA = Fire Growth Rate THR = Total Heat Release SMOGRA = Smoke Growth Source Michael Sommer, BYK-Chemie GmbH, reproduced with permission. ... 

An important characteristic is the fire growth rate (FIGRA), which is calculated by dividing the heat released when the product bums by the time at which a specific rate of heat release is reached. It should correlate to the time to flashover in the room comer test. 

While the overall growth of composites in the aerospace industry is continuing, epoxy has been facing stiff competition from other materials and the growth rate has been relatively small (2% annually). While epoxies are still used in many exterior aircraft parts, carbon fiber composites based on bismaleimide and cyanate esters have shown better temperature and moisture resistance than epoxies in military aircaft applications. In the commercial aircraft arena, phenolic composites are now preferred for interior applications because of their lower heat release and smoke generation properties during fires. High performance thermoplastics, such as polysulfone, polyimides, and polyetherether ketone (PEEK), have also foimd some uses in aerospace composites. 

The use of sandwich panel walling, containing polystyrene (used as thermal insulation for areas such as cold storage facilities), has historically resulted In rapid fire growth, due to the substantial heat release of the building material, i.e. the polystyrene. The failure of component parts, due to the rapid fire growth rate of the materials, also has the ability to destabilise the panels and cause premature collapse. 

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