Chemical process safety explosion-hazards evaluation

FIG. 23-4 Flammability diagram for methane at an initial temperature and pressure of 25°C and 1 atm. [C. V. Mashuga and D. A. Crowl, Application of the Flammability Diagram for Evaluation of Fire and Explosion Hazards of Flammable Vapors," Process Safety Progress, vol. 17, no. 3 copyright 1998 American Institute of Chemical Engineers (AIChE) and reproduced with permission. ]... 

The Dow Fire and Explosion Index (FEI) (12) and the Dow Chemical Exposure Index (CEI) (14) are two commonly used tools that measure inherent safety characteristics. Gowland (25) reports on the use of the FEI and CEI in the development of safety improvements for a urethane plant. Tables 1 and 2 illustrate the application of the FEI and CEI in measuring inherent safety characteristics of process design options. These indices measure the inherent safety characteristics of processes in only two specific areas—fire and explosion hazards and acute chemical inhalation toxicity hazards. Other indices would be required to evaluate other types of hazards. 

Many times companies focus agreat deal of effort on the successful execution of the process to manufacture an acceptable product but leave out employee safety precautions. Protecting equipment and facility structures from harsh chemicals is very important, but protection of your most critical asset—the employee—should be paramount. If specific personnel protection equipment is needed for particular steps, indicate those requirements in the batch record. Also, evaluate the potential of high-pressure air lines or explosion hazards. 

The first step in minimizing accidents in a chemical phuit is to evaluate the facility for potential fires, explosions, and vulnerability to other liazards, particularly those of a chemical miture. This calls for a detailed study of plant site and layout, materials, processes, operations, equipment, and training, plus an effective loss prevention program. The technical nature of industry requires detailed data and a broad range of experience. Tliis complex task, today becoming the most important in plant design, is facilitated by the safety codes, standiu ds, and practice information available. The technical approach to evaluating die consequences of hazards is discussed later in tliis cliapter and in Part V (Chapters 20 and 21). 

The safety and loss prevention guide developed by the Dow Chemical Company provides a method for evaluating the potential hazards of a process and assessing the safety and loss-prevention measures needed. In this procedure, a numerical Fire and Explosion Index is calculated, based on the nature of the process and the properties of the materials. The index can be used two different ways. In the preliminary design, the Dow index will indicate whether alternative,... 

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