Hazard factors

The basis of the F El is a Material Factor (MF). The MF is then multiplied by a Unit Hazard Factor, F3, to determine the F El for the process unit. The Unit Hazard factor is the product of two factors which take account of the hazards inherent in the operation of the particular process unit the general and special process hazards, see Figure 9.2. 

The first step is to calculate the Damage factor for the unit. The Damage factor depends on the value of the Material factor and the Process unit hazards factor (F3 in Figure 2). It is determined using Figure 8 in the Dow Guide. 

The general process hazard factor (Ft) and special process hazard factor (F2) are multiplied together to produce a unit hazard factor (F3). The Dow F EI is computed by multiplying the unit hazard factor by the MF. Table 10-2 provides the degree of hazard based on the index value. 

The purpose of the Dow Fire and Explosion Hazard Index (Dow, 1987) is to 1) quantify the expected damage of potential fire and explosion incidents in realistic terms, 2) identify equipment that would be likely to contribute to the creation or escalation of an incident and 3) communicate the fire and explosion risk potential to management. The Dow Index is the product of the Unit Hazard Factor and the Material Factor (Table 1). 

The Unit Hazard Factor for process unit is the product of general and special process hazards. Penalties of general process hazards deal with different... 

In the Mond Index the plant is divided into individual units on the basis of the feasibility of creating separating barriers. One of the factors taken into account in the index is therefore plant layout. The potential hazard is expressed in terms of the initial value of a set of indices for fire, explosion and toxicity. A hazard factor review is then carried out to see if design changes reduce the hazard, and intermediate values of the indices are determined. Offsetting factors for preventative and protective features are applied and the final values of the indices, or offset indices, are calculated. The elements of the Mond method are listed in Table 1. 

Fig. 6. Procedure for calculating unit hazard factor F E index.

The penalties comprising the unit hazard factor are calculated based on a single, specific instant in time during which the material represented by the MF is associated with the process unit in the most hazardous state of operation. Start up, general operation, and shut down are among the operational states that should be considered. 

Unit hazard factor Material factor Damage factor F E index Exposure radius... 

Although both process units have a unit hazard factor (F3) of 4.0, the final measurement of their probable loss exposure must include the hazard of the material being processed or handled. 

If process unit B had a unit hazard factor of 2.7 instead of 4.0, the F EI would be the same as that of process unit A, 64. However, the damage factor for process unit B would be 0.64 (based on a material factor of 24), compared to a damage factor of 0.45 (based on a material factor of 16) for process unit A. 

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