CALCULATING THE POTENTIAL RISKS

The Potential Risks P, P1 and P2 are defined as products of the fire load factor q, the spread factor i, the venting factor v, the area factor g, the level factor e, and the access factor z. The first three factors are defined by the fire development, the last three by the fire compartment environment

The fire load factor q indicates how much can burn per area unit (m²). It is a measure for the fire duration. In practice, the "FRAME" calculation sheet provides tables with reasonable estimates of the values of Qi (fire load immobile) and Qm ( fire load mobile) based on building construction types and occupancy classification. The formula for the calculation of the fire load factor is :

The fire spread factor i indicates how easy a fire can spread through a building. It corresponds with the growing phase of the fire. It is calculated from the average dimension of the content m, the flame propagation class M, and the destruction temperature T. "FRAME" gives guidelines how to define these parameters.

The venting factor v indicates the influence of smoke and heat inside the building. It compares the venting capacity of the compartment with the sources of smoke and evaluates the flash-over conditions. It is calculated with the smoke venting factor k, the ceiling height and the mobile fire load Qm by the following formula:

The area factor g indicates the horizontal influence of the fire. It is linked to the size and the shape of the fire compartment. It evaluates the fire frequency and the fire fighting access possibilities. The factor g is calculated with the values of l, the theoretical length of the compartment, and of b, the equivalent width, expressed in meter. The length "l" of a compartment is the longest distance between the centres of two sides of the compartments’ perimeter. The equivalent width "b" is the quotient of the total area of the compartment by the theoretical length. The formula is:

The level factor e indicates the vertical influence of the fire and will be calculated from the level number E. The main access level has number E = 0. Levels above the access are numbered 1, 2, 3, etc. Levels below the access level are numbered -1, -2, -3, etc. The formula represents an S-shaped influence curve.

The access factor z is an aggravating factor for compartments where outside help can difficultly reach the fire area. It is calculated by a formula that considers the distance between the access level and the fire area level, the number of access directions and the size of the compartment.