Explosions protection systems

Stanley Grossel, President, Process Safety Design, Inc. Fellow, American Institute of Chemical Engineers Member, American Chemical Society Member, The Combustion Institute Member, Explosion Protection Systems Committee of NFPA (Section 26, Process Safety)... 

Depending upon the design criteria of the installed suppression system, an unsuppressed explosion overpressure of around 7 to 10 bar is reduced to a suppressed reduced explosion overpressure which lies in the range of Fred,max = 0-2 to 1 bar. Thus, vessels need to be explosion resistant for an overpressure of maximum 1 bar (ISO Standard 6184/4, Explosion Protection Systems Paii 4 Determination of Efficacy of Explosion Suppression Systems, Geneva, 1985). 

Arrange qualified outside contractors for periodic testing and emergency maintenance of specialized fire and explosion protective systems. 

NFPA (National Fire Protection Association) 68, Explosion Protection Systems. NFPA, Batterymarch Park, Quincy, Massachusetts, 1988. 

If a general reference is made to explosion protected apparatus or explosion protected systems, then this relies upon zone 1 apparatus. And this will be the guideline throughout all chapters in this book. 

In classic intrinsically safe instrumentation multicore cables lead from the control room into the explosion protected system. Several sensors/actuators are wired to a terminal box and connected to the multicore cable. 

Fire and explosion protection system drawings or arrangements (fire gas detection/alarm, protection - passive and active). ... 

The maximum explosion pressure and the maximum rate of pressure rise (dP/dOmax used to design the explosion protection system and are discussed below. 

BS 6713-3-86. Explosion protection systems. Method for determination of explosion indices of fiiel/air mixtures other than dust/air and gas/air mixtures (ISO 6184-3). 

Fire and explosion protection systems drawings and arrangements (e.g., fire and gas detection/alarm, protection—passive/aggressive)... 

FIGURE 48.14 Normographs for the sizing of vent relief explosion. (From Explosion Venting, NEPA No. 68, National Fire Protection Association, Quincy, MA, 1988 (presently under revision by the NFPA Explosion Protection Systems Committee.)... 

The following appendices provide references to standards, fire resistance nomenclature, electrical ratings, hydraulic data, and conversion factors commonly referred to while examining and designing fire and explosion protection systems for the process industry. 

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. 

Standard on Explosion Prevention Systems NFPA 69, National Fire Protection Association, Quiacy, Mass., 1986. 

For any proposed suppression system design, it is necessary to ascribe with confidence an effective worst-case suppressed maximum explosion overpressure Pred.max- Provided that the suppressed explosion overpressure is less than the process equipment pressure shoclc resistance and provided further that this projected suppression is achieved with a sufficient margin of safety, explosion protection security is assured. These two criteria are mutually independent, but both must be satisfied if a suppression system is to be deployed to provide industrial explosion protection. 

National Fire Protection Association (NFPA) (1992). Explosion Prevention Systems. NFPA 69, Quincy, MA NFPA. 

Mitigation System Resmnses Dikes and drainage. Hares, Fire protection systems (active and passive). Explosion vents. Toxic gas absorption... 

An explosion occurred in a vapor-phase hydrocarbon oxidation plant, injuring ten people and seriously damaging the plant, despite the fact that it was fitted with a protective system that measured the oxygen content and isolated the oxygen supply if the concentration approached the flammable limit. 

The test took more than an hour. The protective system was therefore out of action for about 5% of the time. There was a chance of 1 in 20 that it would not prevent an explosion because it was being tested. It was, in fact, under test when the oxygen content rose. 

Lapp, K. and Werneburg, H. 1999. Detonation Flame Arrester Qualifying Application parameters for explosion Protection m Vapour Handling Systems./. Can. Petrol. TechuoL, Special Edition 1949-1999, Paper 94-58. 

Table 7-31 lists the explosibility index that is a relative measure of the potential damage from a dust explosion. A rating of 2 to 4 requires large vent areas. Above 4, for most cases, the explosion cannot be controlled by venting design and therefore requires the use of protection such as inert gas or explosive suppression systems, some of which are commercially available. 

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