Fire and explosion index

Methods for performing hazard analysis and risk assessment include safety review, checkhsts, Dow Fire and Explosion Index, what-if analysis, hazard and operabihty analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

Dow Fire and Explosion Index. The Dow Eire and Explosion Index (3) is a procedure usehil for determining the relative degree of hazard related to flammable and explosive materials. This Index form works essentially the same way as an income tax form. Penalties are provided for inventory, extended temperatures and pressures, reactivity, etc, and credits are appHed for fire protection systems, process control (qv), and material isolation. The complete procedure is capable of estimating a doUar amount for the maximum probable property damage and the business intermptionloss based on an empirical correlation provided with the Index. 

EinaHy, the penalties are factored into the original material factor to result in a fire and explosion index value. The higher this value, the higher the degree of hazard. 

The next step is to apply a number of loss control credit factors such as process control (emergency power, cooling, explosion control, emergency shutdown, computer control, inert gas, operating procedures, reactive chemical reviews), material isolation (remote control valves, blowdown, drainage, interlocks) and fire protection (leak detection, buried tanks, fire water supply, sprinkler systems, water curtains, foam, cable protection). The credit factors are combined and appHed to the fire and explosion index value to result in a net index. 

Fire and Explosion Index (Ffrom fires and explosions. frequency The rate at which observed or predicted events occur. HAZOP HAZOP stands for hazard and operabihty studies. This is a set of formal hazard identification and ehmination procedures designed to identify hazards to people, process plants, and the environment. See subsequent sections for a more complete description. 

Davison, G., and Hewitt, C.N. (ed.) (1997) Air Pollution in the United Kingdom, Royal Society of Chemistry, London. Dow Chemical Company (1993) Dow s Fire and Explosion Index Hazard Classification Guide American Institute of Chemical Engineers. 

Dow Fire and Explosion Index (F EI) A method (developed by Dow Chemieal Company) for ranking the relative fire and explosion risk assoeiated with a proeess. Analysts ealeulate various hazard and explosion indexes using material eharaeteristies and proeess data. 

Tools are available to assist in comparing the risk associated with two or more different processes. For example, the first sheet of the Dow Fire and Explosion Index (FEI) (Dow, 1994b) ranks the safety characteristics of the process from a fire/explosion standpoint, without taking credit for protective and mitigation features. The Dow Chemical Exposure Index (CEI) (Dow, 1994a) and Id s Mond Index (ICI, 1985 Tyler, 1985) are other ranking tools. 

Dow Chemical Company (1994b). Dow s Fire and Explosion Index Hazard Classification Guide. 7th Edition. New York American Institute of Chemical Engineers. 

The approach to developing metrics for process safety is analogous to those that might be used to assess Occupational Exposure risk. One can cite as well several indices that have been developed as metrics for estimating and ranking the safety of a given process or chemical reaction, such as the DOW fire and explosion index,the Stoessel index ° for hazard assessment and classification of chemical reactions, the Inherent Safety Index, the Prototype Index for Inherent Safety, amongst others. ... 

Other techniques that take into account some site-specific conditions, such as the Dow Fire and Explosion Index (Ref. 34) and the Mond Index (Ref. 39), have been used to prioritize buildings for evaluation. The results of these indices should be used in conjunction with consideration of other factors, rather than as stand-alone criteria. These other factors might include an evaluation of the effects of confinement and/or congestion-induced turbulence on the potential for blast. 

A numerical Fire and explosion index (F El) is calculated, based on the nature of the process and the properties of the process materials. The larger the value of the F El, the more hazardous the process, see Table 9.3. 

Fire and explosion index range Degree of hazard... 

Figure 9.1. Procedure for calculating the fire and explosion index and other risk analysis information. From Dow (1994) reproduced by permission of the American Institute of Chemical Engineers. 1994 AIChE. All rights reserved.

Figure 9.2. Dow Fire and Explosion Index calculation form.

An estimate is then made of the area (radius) of exposure. This represents the area containing equipment that could be damaged following a fire or explosion in the unit being considered. It is evaluated from Figure 7 in the Guide and is a linear function of the Fire and Explosion Index. 

The individual fire and explosion indexes are combined to give an overall index for the process unit. The overall index is the most important in assessing the potential hazard. 

Figure 9.2a. Fire and explosion index calculation form, Example 9.1.

More detailed check lists are given by Carson and Mumford (1988) and Wells (1980). Balemans (1974) gives a comprehensive list of guidelines for the safe design of chemical plant, drawn up in the form of a check list. A loss prevention check list is included in the Dow Fire and Explosion Index Hazard Classification Guide, Dow (1987). 

The protective features recommended depend on this index and are given in reference 15. For instance, for an area subject only to fire an explosion or blast wall is not required unless the Fire and Explosion Index exceeds 40. For an index below 20 a ventilation rate that would result in total change of the air in the building every... 

A hazards survey can be as simple as an inventory of hazardous materials in a facility or as complicated as a rigorous procedure such as the Dow Fire and Explosion Index (F EI)2 and the... 

The procedure begins with a material factor that is a function only of the type of chemical or chemicals used. This factor is adjusted for general and special process hazards. These adjustments or penalties are based on conditions such as storage above the flash or boiling point, endo- or exothermic reactions, and fired heaters. Credits for various safety systems and procedures are used for estimating the consequences of the hazard, after the fire and explosion index has been determined. 

The first step in the procedure is to conceptually divide the process into separate process units. A process unit is a single pump, a reactor, or a storage tank. A large process results in hundreds of individual units. It is not practical to apply the fire and explosion index to all these units. The usual approach is to select only the units that experience shows to have the highest likelihood of a hazard. A process safety checklist or hazards survey is frequently used to select the most hazardous units for further analysis. 

Figure 10-3 Form used in the Dow Fire and Explosion Index. The figures and tables referenced in the form are provided in the index booklet. Source Dow s Fire and Explosion Index Hazard Classification Guide, 7th ed., (1994). Reproduced by permission of the American Institute of Chemical Engineers.

---