Explanation of the Dow Fire and Explosion Index. The Fire and Explosion Index (F&E!) calculation is a tool to help determine the areas of greatest loss potential in a particular process. It also enables one to predict the physical damage that would occur in the event of an incident. The first step in making the F&EI calculation requires using an efficient and logical procedure to determine which process units should be studied. A process unit is defined as any major item of process equipment. The following process units could be identified in a typical plant. • • • • • • • Unloading facility Storage tank Reactor Distillation Column Quench Vessel Storage Vessel Loading facility A designation of the Process Unit must be entered in the appropriate space on the F&EI form. The Manufacturing Unit designation must also be entered on the F&EI form. A Manufacturing Unit is the entire production facility including chemical processes, mechanical processes, warehouse, packaging lines, etc. It is quite clear that most manufacturing units have many process units. To calculate the Fire and Explosion Index, however, only process units that could have an impact from a loss prevention standpoint should be evaluated. These are known as Pertinent Process Units. Important factors for selecting Pertinent Process Units include: a. Chemical energy potential (Material Factor) b. Quantity of hazardous material in the Process Unit c. Process pressure and process temperature d. Units critical to plant operation, e.g. Reactor Important Considerations A. The Fire and Explosion Index system assumes that a process unit handles a minimum of 2,500 kg of a flammable, combustible or reactive material. If less material is involved, generally the risk will be overstated. However, F&EI calculations can provide meaningful results for pilot plants if they handle at least 500 kg) of combustible or reactive material. Careful consideration is needed when equipment is arranged in series and the items are not effectively isolated from each other. An example would be a reaction train without an intermediate pump. In such situations, the type of process determines whether several vessels or just a single vessel should be considered as the Process Unit. B. It should rarely be necessary to calculate the F&EI for more than three or four Process Units in a single process area of a Manufacturing Unit. By their nature. steady-state operation. A separate F&EI form must be completed for each process unit evaluated. . Generally. etc. such normal stages as startup. filling.. emptying. often create unique conditions having an impact on the F&EI. It is also important to give careful consideration to the state or point in time of the operation. Occasionally more than one point in time will have to be studied to determine the significant risk. shutdown. good judgment will enable selection of the point in time of operation to perform the F&EI calculation. adding catalyst. The number of Process Units will vary according to the type of process and the configuration of the Manufacturing Unit. C. The flammability ranking of liquids and gases is obtained from flash point data.DETERMINATION OF MATERIAL FACTOR The Material Factor (MF) is the basic starting value in the computation of the F&EI and other risk analysis values. MATERIAL FACTOR DETERMINATION GUIDE Flammability Ranking Non-combustible2 F. Definitions in National Fire Protection Association (NFPA) 704 should be used to assign hazard ratings for materials which are not listed in the F&EI calculation tool in S2S. the flammability and instability rankings may possibly be found in NFPA 325M or NFPA 49 adjusted for temperature. and used with Table l to determine the MF. if appropriate.8 °C) ≤ 200 °F (≤ 93.3 °C) Instability Ranking 1 4 10 14 14 14 24 24 24 29 29 29 40 40 40 0 1 2 . The MF is obtained from the flammability and instability rankings according to NFPA 704. and the St of dusts or mists is determined by dust explosion testing. Generally. The fire hazard from a combustible liquid at a temperature above its flash point is equivalent to that from a flammable liquid at ambient temperature. First. It is recognized that the fire and reaction hazards of a material increase markedly with temperature. Unlisted Substances If neither Appendix A. NFPA 49. as discussed below under C. If the temperature of the material on which the MF is based is over 140 °F (60 °C). use the Dust Hazard Class Number (St number) rather than the flammability ranking. > 200 °F (> 93. Reaction rates also increase very markedly with temperature. > 100 °F (> 37. a certain adjustment may be required.” Appendix A provides a listing of MFs for a number of chemical compounds and materials. nor NFPA 325M contains values for the substance. If the material is a combustible dust. the parameters shown in the left column of the table will have to be determined. “Temperature Adjustment of Material Factor. the flammability and instability rankings are for ambient temperatures.P. A. mixture or compound in question. and these values will be used in most cases. The MF is a measure of the intrinsic rate of potential energy release from fire or explosion produced by combustion or chemical reaction. If Appendix A does not list the material.P.3 °C) F. The flammability ranking of combustible solids depends on the nature of the material as categorized in the left column. mixture or compound at ambient temperature. these values will have to be determined from the flammability ranking or dust class (St) (see Table l). The instability ranking can be obtained from a qualitative description of the instability (or reactivity with water) of the substance. F 3. The numerical value of the Process Unit Hazards Factor is determined by first determining the General Process Hazards Factor and Special Process Hazards Factor listed on the F&EI form.P. 6 Includes rubber goods such as tyres and boots. fiber. 3 K values are for a 16 Litre or larger closed test vessel with strong ignition source.8 °C) F. PROCESS UNIT HAZARDS FACTORS After the appropriate Material Factor has been determined. etc. rack storage. it can be certain that the Fire and Explosion analysis will really be based upon a . magnesium ingots.8 °C) & BP.8 °C) 3 16 16 24 29 40 4 21 21 24 29 40 Combustible Dust or Mist3 St-1 (KSt ≤ 200 bar m/sec) St-2 (KSt = 201-300 bar m/sec) St-3 (KSt > 300 bar m/sec) 16 21 24 1 2 3 4 10 16 16 21 24 14 14 16 24 24 24 24 24 24 29 29 29 29 29 29 40 40 40 40 40 40 Combustible Solids Dense > 40 mm thick4 Open < 40 mm thick5 Foam. which is the term that is multiplied by the Material Factor to obtain the F&EI. < 73 °F (< 22.F. wood pallets and non-dusting ground material such as polystyrene.8 °C) < 100 °F (< 37. = Flash Point. = Boiling Point at Standard Temperatures and Pressure (STP) Notes: 1 Includes volatile solids. When calculating the penalties comprising the Process Unit Hazards Factor.8 °C) & B. Guide for Venting of Deflagrations. Since the MF is taken to be that of the most hazardous substance present in the Process Unit. This rather strict definition is intended to prevent double or triple counting of hazards occurring during the process. < 100 °F (< 37. 2 Will not burn in air when exposed to a temperature of 816 °C for a period of five minutes. tight stacks of solids and tight rolls of paper or plastic film5 Includes coarse granular material such as plastic pellets. See NFPA St 68.6 F.P. powder. continuous operation and shutdown are among the operational states that may be considered. ≥ 73 °F (≥ 22. < 73 °F (< 22.P.8 °C) or F. 4 Includes wood – 2 inches nominal thickness.P. the next step is to calculate the Process Unit Hazards Factor (F3). Startup. ≥ 100 °F (≥ 37. pick a single specific instant in time during which the material under consideration is in the most hazardous normal operation state associated with the Process Unit. closed cup B. Each item which contributes to the Process Hazards Factors contributes to the development or escalation of an incident that could cause a fire or an explosion.P.P. For those that do not. startup. Keep the focus on the Process Unit and Material Factor selected for analysis and keep in mind that the results of the final calculation are only as valid as the appropriateness of the penalty assessments. Remember – analyze only one hazard at a time. most hazardous time (e. If the MF is based on a flammable liquid present in the Process Unit. and this will be a realistic worst case — one that could actually occur. A reasonable approach might be to evaluate the Process Unit once using the MF of the flammable liquid and a second time using the MF of the dust. even though dust may be present at a different time. Only the calculation resulting in the highest F&EI and Actual Maximum Probable Property Damage need to be reported.” If a hybrid mixture is selected as the most hazardous material present. relating the analysis to a specific. described previously under “Mixtures. the results give an indication of the ranking of risk of each unit relative to another.xls When the indexes for all pertinent units in the plant have been calculated.. do not take penalties relating to combustible dusts . . The entry of all the pertinent information to allow calculation of the Fire and Explosion Index and the radius of exposure is made in the excel workbook F&EI Calculation workbook S2S July 2006. This ranking can be used for screening out the lower risk items and concentrating study on the higher ones. In the F&EI system. Some items on the F&EI form have fixed penalty values.“worst case” when focus is placed on the most hazardous operational point involving the MF.g. normal operation or shutdown). it is penalized both as a dust and as a flammable vapor in the Process Unit Hazards Factor sections of this manual. One important exception is the hybrid. determine the appropriate penalty by consulting the text that follows. only one hazard may be evaluated at a time.