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SAFETY AND LOSS PREVENTION
9.4. DOW FIRE AND EXPLOSION INDEX
The hazard classification guide developed by the Dow Chemical Company and published
by the American Institute of Chemical Engineering, Dow (1994) (www.aiche.org), gives
a method of evaluating the potential risk from a process, and assessing the potential loss.
A numerical “Fire and explosion index” (F & EI) is calculated, based on the nature
of the process and the properties of the process materials. The larger the value of the
F & EI, the more hazardous the process, see Table 9.3.
Table 9.3. Assessment of hazard
Fire and explosion index range Degree of hazard
1 60 Light
61 96 Moderate
97 127 Intermediate
128 158 Heavy
>159 Severe
Adapted from the Dow F & EI guide (1994).
To assess the potential hazard of a new plant, the index can be calculated after the
Piping and Instrumentation and equipment layout diagrams have been prepared. In earlier
versions of the guide the index was then used to determine what preventative and
protection measures were needed, see Dow (1973). In the current version the preven-
tative and protection measures, that have been incorporated in the plant design to reduce
the hazard are taken into account when assessing the potential loss; in the form of loss
control credit factors.
It is worthwhile estimating the F & EI index at an early stage in the process design, as
it will indicate whether alternative, less hazardous, process routes should be considered.
Only a brief outline of the method used to calculate the Dow F & EI will be given in
this section. The full guide should be studied before applying the technique to a particular
process. Judgement, based on experience with similar processes, is needed to decide the
magnitude of the various factors used in the calculation of the index, and the loss control
credit factors.

9.4.1. Calculation of the Dow F & EI
The procedure for calculating the index and the potential loss is set out in Figure 9.1.
The first step is to identify the units that would have the greatest impact on the
magnitude of any fire or explosion. The index is calculated for each of these units.
The basis of the F & EI is a Material Factor (MF). The MF is then multiplied by a Unit
Hazard Factor,F 3 , to determine the F & EI 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.

Material factor
The material factor is a measure of the intrinsic rate of energy release from the burning,
explosion, or other chemical reaction of the material. Values for the MF for over 300 of