Fuel Packages for 3-D simulations

3-D fire simulators that are used as engineering tools for safety purposes, still require the user to input data such as the evolution with time of the heat release rate (HRR), which describes the fire from its ignition to its extinguishment, as well as the evolution with time of the species produced by the combustion of the different flammable building contents. The HRR history is assumed to be determined from single HRR curves established with furniture calorimeter tests and translated in time when the ignition of the subsequent building contents is estimated, according to a pre-established fire scenario. This project aims to create a comprehensive database of HRR curves for a range of combustible building contents so that the fire protection engineer can select the data which is the most appropriate to a fire protection engineer project.

Fuel packages for 3-D fire simulators include:

- a 3-D geometry, which represents the spatial configuration of the combustible package, as its external envelope,
- the description of the evolution with time of the burning surfaces of the 3-D geometry.

The characteristics of the burning surfaces will determine the HRR history as well as the production of fire effluents.

The final product of this project is intended to create "fuel packages" to be used in the Fire Dynamics Simulator (FDS) developed by the US National Institute of Standards and Technology (NIST) since this computational Fluid Dynamics is available for free and largely used by the Fire Protection Engineering community. Nevertheless, it is expected that the 'fuel packages" will be described with enough details that they could be used for other CFD fire simulators.

The advantage of having discrete "fuel packages" for 3-D simulations is to be used by Fire Protection Engineers to estimate the ignition of secondary fuel sources located nearby the 'fuel package' on fire. Ignition of secondary fuels is mainly dependent on the thermal radiation received by these fuels. The received radiation is a function of the distance between the two types of fuel sources and the power of the radiative "fuel package" emitter.

The figures below present an example of the process followed in order to implement the ‘combustible package’ database, for a mattress ignited at its center. The 3-D Fire Dynamics Simulator (FDS) from NIST has been used to recreate this experiment.

Evolution with time of the Heat Release Rate of a mattress with central ignition
On the left: experimental data extracted from a NIST resource
On the right: comparison between the experimental data and a FDS simulation

In addition to the HRR curve, the database gathers information related to the dimensions of the ‘combustible package’, the applied ignition source, videos or snapshots of the experiment showing flame spread, evolution with time of the fire effluents.

Snapshots of an experiment involving the combustion of a mattress with central ignition (source: NIST)
From left to right: at 90 seconds, at 120 seconds, at 210 seconds, at 300 seconds

Snapshots of the corresponding FDS simulation at the same moments (200 kW.m-3)

Productions of fire effluents (toxic and irritant products) as well as soot are data required for assessing toxicity and loss of visibility during fire events. FDS allows the use of ‘burners’ which can also emit species such as HCN, CO2, CO, HCl and soot, as a function of time, specified by the user. Some of the furniture calorimeter experiments contain this data. For these ‘combustible packages’, the data will include fire effluent productions (in over-ventilated conditions and under-ventilated conditions when available) as well as the HRR curve

Nevertheless, it should be noted that the data related to fire effluent production is sparse. It is often given as a global mass yield (i.e. mass of a considered fire effluent produced, divided by the mass of fuel consumed), or as a global CO/CO2 ratio as this parameter is an indicator of the ventilation conditions.

In absence of fire effluent data for a ‘combustible package’ from furniture calorimeter tests, data gathered from cone calorimeter tests or other laboratory-scale tests may be considered.