Use of the fire load
Nowadays, the fire load is one of the factors that are taken into account when it assessed the risk of fire. This is applied in the Regulation of Fire Safety in Industrial facilities (hereinafter, RSCIEI). In order to characterize the industrial facilities, besides the type of building, it is necessary to calculate the intrinsic risk level through the load density of the industrial area considered. The calculation of the fire load must be very precise, depending on this value, a value of the intrinsic risk level will be obtained. The importance of this value is associated to the fact that the measures collected in the RSCIEI to prevent the start of fire and its subsequent fire spread, will be depending on this value (size of the enclosures, reaction and resistance to fire, evacuation, temperature control and smoke exhaust systems and fire protection installations).
Now, it is showed the intrinsic risk level value as a function of the fire load density.
Table 1. Source: Real Decreto 2267/2004. (RSCIEI).
Moreover and to have a calculation as accurate as possible, it must be included in the value of the fire load density (expression 1 of the RSCIEI) the corresponding one contributed by the construction materials that have by themselves a calorific potential greater than zero. In most cases, the contribution will be very small compared to the fire load of the enclosure but it has to be accounted for. The percentage of participation of the construction materials at the load density according to the level of intrinsic risk considered, will depend mainly on the type of product, thickness, density, etc.
How can you know the fire load?
In the case of RSCIEI, this regulation includes a series of tables showing the fire load of different products used in manufacturing and sales activities or in storage activities. The units of the fire load in this case are shown per unit area or volume depending on the case. In the case of construction products, this determination can be carried out through the test according to the EN ISO 1716 standard «Determination of the gross heat of combustion (calorific value)». This is one of the tests included in the European system for evaluating the reaction to fire.
As I mentioned in the post titled How is fire reaction evaluated?, this system uses a series of letters to categorize the reaction behaviour of a material, product or system in case of fire.
Where is fire load indicated?
Not for all Euroclasses it is necessary to determine the fire load. This determination is mandatory for classes A1 and A2 and may be consulted in the classification and test report. On one hand If the material or product were homogeneous, the gross of heat combustion (hereinafter PCS) would be expressed in MJ/kg. On the other hand, if the product or system is heterogeneous, the classification standard requires a maximum value in MJ/kg for the complete product but also requires a maximum value of the PCS for each component of the product or system but this time in MJ/m2.
How is a multi-layer product evaluated?
First, the PCS value must be available in MJ/kg for the individual components of the product. In this case, we will see that some materials, such as adhesives or paints, usually present values between 20 MJ/kg and 40 MJ/kg. This causes that in some occasions, it is thought that the product will not reach the desired class because the individual PCS is high. But in this case, the standard indicates that the total PCS will be determined per unit area, that is, the present quantity of each material in the final product will be taken into account. This is quantified through the surface density and will be expressed in Kg/m2. In this way, the PCS of the multilayer product will be available in MJ/kg and in MJ/m2.
Relationship between fire load and flammability
When a fire occurs and the products of the enclosure are affected, each of them will behave in a specific way, that is, not all the fire load will be released at the same time of the fire, but there will be products that release the load of fire of progressive way not releasing all the heat when they are affected by the first flames (Typical in products that produce carbonization when they are attacked by a heat source). There will be other cases that by application of superficial treatments or paintings onto products with low valuesof the PCS, could produce a flame in an early phase contributing a great amount of heat to the system in a short space of time. We can also find products that have a relatively high PCS but release a reduced amount of heat due to the presence of flame retardants or other products to improve fire behaviour.
Therefore, it will be essential to know the specific behaviour of each product in case of fire and therefore it cannot be stated categorically that the greater the fire load, the greater the flammability.
Antonio Galán Penalva Fire safety consultant