Process hazards fires

Fire and uncontroUed polymerization are a concern in the handling of chloroprene monomer. The refined monomer is ordinarily stored refrigerated under nitrogen and inhibited. This is supported by routine monitoring for polymer formation and vessel temperature. Tanks and polymerization vessels are equipped for emergency inhibitor addition. Formalized process hazard studies, which look beyond the plant fence to potential for community involvement, are routine for most chemical processes. 

Hydroprocesses Hydrogen is chemically stable and relatively unreactive at ordinary temperatures most processes utilizing it require a catalyst. Above 500°C it reacts readily with oxygen and confined flammable mixtures explode violently if ignited Main hazards fire, explosion, metallurgical problems arising from hydrogen attack... 

Complete and accurate written documentation of chemicals properties, process teclinology, and process equipment is essential to the PSM program and to a process hazards analysis (PrHA). This information serves many users including the PrHA team. The needed chemical information includes fire and explosion characteristics, reactivity hazards, safety and health hazards and the corrosion and erosion effects. Current material safety data sheet (MSDS ) information helps meet this requirement, but must be supplemented with process chemistry information regarding runaway reactions, and over-pressure hazards. 

In 1968, after many years experience in plant operations, I was appointed safety adviser to the heavy organic chemicals division (later the petrochemicals division) of Imperial Chemical Industries. My appointment followed a number of serious fires in the 1960s, and therefore I was mainly concerned with process hazards rather than those of a mechanical nature. 

The results of previous process hazards evaluations may be used if it can be confirmed that the reviews adequately addressed explosion and fire risks to process plant buildings. ... 

In a joint research project in Sweden under the main title "Fire hazard - Fire growth in compartments in the early stage of development (pre-flashover)" (1, 2) a number of different factors have been studied. In the process of developing a full-scale fire test method - "room-corner" configuration - for surface lining materials, Nordtest NT-FIRE 025, the emission of smoke and gas was studied. That study covers data from thirteen different single and... 

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 frequently used Dow Fire Explosion Hazard Index (1987) gives penalties for fired equipment and certain specified rotating equipment. These are a part of the Special Process Hazards term of the Dow Index. 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

On the other hand, there are a number of elements of fire prevention that overlap with elements of other programs. For example. Incident Investigation, Management of Change (MOC), Process Safety Information (PSI), and Process Hazard Analysis (PHA) input required for fire prevention can be derived from these same elements of the Process Safety Management (PSM) program. 

Figure 5-1 shows how the FHA is integrated into an overall risk assessment. A process hazard analysis is required to identify likely fire scenarios that are carried forward to the FHA. An FHA provides the tools to characterize the hazards and evaluate consequences. The results are incorporated into an overall risk assessment. See Chapter 6 for more information on fire risk assessment. 

The process hazard analysis can be a starting point for the selection of fire scenarios. The process hazard analysis can be reviewed to develop a list of scenarios that result in fire as a consequence. Generic release sizes for small, medium, and large releases have been proposed as shown in Table 5-1 (Spouge, 1999). This saves time by eliminating the need to develop a detailed scenario. The analyst can use these release sizes to perform fire modeling calculations and determine the impact by moving the release point locations. The release criteria are considered to be representative of scenarios that could reasonably be expected to occur. 

Where the need for fire detection is identified, the required performance of the fire detection system is already specified as part of the grading process. Fixed fire detection is typically installed to protect equipment that is high value, long lead time, or likely to be significant fire escalation hazards. The performance specification defines fire size and response time thresholds for alarm and action(s). Fire hazards are defined by radiant heat output (RHO). RHO gives a reasonable indication of the potential damage and the probability that the fire will escalate or cause loss. The RHO should not be used to determine fire thermal loading onto equipment and structures. Table 8-3 compares RHO and flame area for some typical hydrocarbon fires. 

There are innumerable situations where gases, liquids, and hazardous chemicals are produced, stored, or used in a process that, if released, could potentially result in a hazardous fire condition. It is important to analyze all materials and reactions associated with a particular process, including production, manufacturing, storage, or treatment facilities. Each process requires analysis of the potential for fire. 

As an example, styrene polymerizes at ordinary temperatures and the rate of polymerization increases as temperature increases. The reaction is exothermic and becomes violent as it is accelerated by its own heat. Inhibitors are added to prevent the initiation of dangerous polymerization. When the styrene is used to fabricate materials, e.g., fiberglass resin, a catalyst may be added in the manufacturing process to initiate polymerization at a controlled rate. Any unbalance of these reactions in terms of quantities or temperatures could cause hazardous fire conditions. 

PHAST (Process Hazard Analysis Software Tool)—This is a conglomerate package for gas dispersion and fire modeling. PHAST is capable of calculating the formation of a cloud or pool to final dispersion calculating concentrations, fire radiation, toxicity, and explosion overpressure endpoints. 

The plant shutdown (which distracted the operators and made the electric fire water pump unavailable) was caused by a thunderstorm that tripped the primary feeder and no backup feeder was installed. The unit should be designed to shutdown safely on loss of power. (Process hazards analysis)... 

Process Hazards Contributing to Fire and Explosion Incidents ... 

Critical process safeguards as alarms and trips. A Process Hazards Analysis may have questioned the lack of a loss of heat transfer fluid flow alarm and burner firing shutdown for a flow loss condition. 

Predictive hazard evaluation procedures may be required when new and different processes, designs, equipment, or procedures are being contemplated. The Dow Fire and Explosion Index provides a direct method to estimate the risks in a chemical process based upon flammability and reactivity characteristics of the chemicals, general process hazards (as exothermic reactions, indoor storage of flammable liquids, etc.) and special hazards (as operation above the flash point, operation above the auto-ignition point, quantity of flammable liquid, etc.). Proper description of this index is best found in the 57-page Dows Fire and Explosion Index, Hazard Classification Guide, 5 th ed., AIChE, New York, 1981. 

The American Petroleum Institute (API) maintains cooperation between U.S. government and industry on all petroleum-related issues of U.S. concern. The API provides process hazards and process safety seminars, but they are best known to some of us for their valuable publications. The API generates easy-to-read and easy-to-understand technical standards of design and fire protection. They also provide equipment inspection guides that are applicable in most plants. Specific information about their large number of standards can be obtained at their website. 

In the aftermath of the Bhopal disaster, OSHA s Process Safety Management (PSM) has come into play and dictates the procedures to minimize the possibility of fire, explosion, or chemical release. If a project contains a regulated hazardous chemical, a process hazards analysis must be conducted to ensure that the likelihood of a fire, explosion, or release of hazardous chemicals is minimized and that equipment and facilities are included to minimize the effects of a fire, explosion, or release, if one does occur. 

Assurances that new and existing chemical processes are conducted safely have never been more needed. Public awareness of the effects of chemical exposure has increased since the early 1970s. Although the initial focus of the Occupational Safety and Health Act of 1970 was on safety, clearly the emphasis now is on health. People at all levels of society are concerned about exposure to chemicals and the possible short- and longterm effects of chemicals on human health. The effects of chemicals on the environment from past or present waste sites, accidental releases or spills, and fires and explosions are reported daily in the news media. Control of all chemical processes to avoid accidental discharges and/or upsets that lead to fires, explosions, and environmental release is essential in the laboratory, the pilot plant, and the manufacturing plant. Chemical process hazard reviews are necessary at each step in the development of a process to ensure that the process can be controlled and conducted so as to minimize the risks to personnel, property, and the environment. 

In the Du Pont Company as a whole, a vigorous program of process hazards management, of which Process Hazards Reviews (PHR s) are but one element, was instituted and has been recommended by our Corporate Safety Fire Protection Division as far back as 1966 (1). 

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