Vapor hazards, explosives

Vapor cloud explosions. Explosions which occur in the open air are vapor cloud explosions. A vapor cloud explosion is one of the most serious hazards in the process industries. Although a large toxic release may have a greater disaster potential, vapor cloud explosions tend to occur more frequently. Most vapor cloud explosions have been the result of leaks of flashing flammable liquids. 

Fire Hazards - Flash Point (deg. F) -70 CC Flammable limits in Air (%) 1.4 - 8.3 Fire Extinguishing Agents Dry chemical, foam, or carbon dioxide Fire Extinguishing Agents Not To Be Used Water may be ineffective Special Hazards of Combustion Products Not pertinent Behavior in Fire This is a highly volatile liquid. The vapors are explosive when mixed with air Ignition Temperature (deg. F) 800 Electrical Hazard Not pertinent Burning Rate 7.4 mm/min. 

The ineident eommander may rely on visual observation of plae-ards, labels, and manifests and information gathered during the response. Obtaining air measurements with monitoring equipment for toxie eon-eentrations of vapors, partieulates, explosive potential, and the possibility of radiation exposure is important for determining the nature, degree, and extent of the hazards [2]. 

Chapters 7, 8, and 9 demonstrate the consequence modeling techniques for vapor cloud explosions, BLEVEs, and flash fires, respectively, by presenting sample problems. These problems contain sufficient detail to allow an engineer to use the methods presented to evaluate specific hazards. 

The long list of vapor cloud explosion incidents indicates that the presence of a quantity of fuel constitutes a potential explosion hazard. If a quantity of flammable material is released, it will mix with air, and a flammable vapor cloud may result. If... 

In the application of the multienergy concept, a particular vapor cloud explosion hazard is not determined primarily by the fuel-air mixture itself but rather by the environment into which it disperses. The environment constitutes the boundary conditions for the combustion process. If a release of fuel is anticipated somewhere, the explosion hazard assessment can be limited to an investigation of the environment s potential for generating blast. 

Prugh, R. W. 1987. Evaluation of unconfined vapor cloud explosion hazards. Int. Conf. on Vapor Cloud Modeling. Cambridge, MA. pp. 713-755, AIChE, New York. 

Stock, M., and W. Geiger. 1984. Assessment of vapor cloud explosion hazards based on recent research results. 9th Int. Symp. on the Prevention of Occupational Accidents and Diseases in the Chemical Industry, Luzern, Switzerland. 

Van den Berg, A. C., C. J. M. van Wingerden, and H. G. The. 1991. Vapor cloud explosion blast modeling. International Conference and Workshop on Modeling and Mitigation the Consequences of Accidental Releases of Hazardous Materials, May 21-24, 1991. New Orleans, USA. proceedings, pp. 543-562. 

A flash fire is the nonexplosive combustion of a vapor cloud resulting from a release of flammable material into the open air, which, after mixing with air, ignites. In Section 4.1, experiments on vapor cloud explosions were reviewed. They showed that combustion in a vapor cloud develops an explosive intensity and attendant blast effects only in areas where intensely turbulent combustion develops and only if certain conditions are met. Where these conditions are not present, no blast should occur. The cloud then bums as a flash fire, and its major hazard is from the effect of heat from thermal radiation. 

In the first approach, a vapor cloud s potential explosive power is proportionally related to the total quantity of fuel present in the cloud, whether or not it is within flammable limits. This approach is the basis of conventional TNT-equivalency methods, in which the explosive power of a vapor cloud is expressed as an energetically equivalent charge of TNT located in the cloud s center. The value of the proportionality factor, that is, TNT equivalency, is deduced from damage patterns observed in a large number of vapor cloud explosion incidents. Consequently, vapor cloud explosion-blast hazard assessment on the basis of TNT equivalency may have limited utility. 

The two approaches lead to completely different procedures for vapor cloud explosion hazard assessment. If conventional TNT-equivalency methods are applied, explosive potential is primarily determined by the amount of fuel present in a cloud, whether or not within flammability limits. The cloud center is the potential blast center and is determined by cloud drift. 

The outcome of a vapor cloud explosion hazard assessment can depend greatly on the method chosen, as demonstrated in this subsection with sample calculations. 

Vapor Cloud Explosion Hazard Assessment of a Storage Site... 

The multienergy method applies only if detonation of unconfined parts of a vapor cloud can be ruled out. If so, the explosive potential of a vapor cloud is determined primarily by the blast-generative properties of the environment in which the vapor is released and disperses. Consequently, a vapor cloud explosion can be regarded as a number of subexplosions. Therefore, the first step in applying the multienergy method in vapor cloud explosion hazard assessment is... 

The key point here is to determine if flammable or combustible materials are being processed under conditions of temperature and pressure such that, if a release occurs, a significant quantity of the material may be released into the air as either a gas, vapor, mist, or aerosol. If such conditions are present, the user should assume that the potential for a vapor cloud explosion exists. Otherwise, VCE hazards can be ignored. 

Process plants are categorized into different hazard classifications, according to the potential explosion energy available from vessel rupture, condensed-phase explosion, confined vapor (building) explosion, or VCE. 

Unconfined explosions. Explosions that occur in the open air are unconfined explosions. An unconfined vapor cloud explosion is one of the most serious hazards in the... 

Richard W. Prugh, Evaluation of Unconfined Vapor Cloud Explosion Hazards, International Conference on Vapor Cloud Modeling (New York American Institute of Chemical Engineers, 1987), p. 713. 

Prugh, Evaluation of Unconfined Vapor Cloud Explosion Hazards, p. 714. 

Daniel A. Crowl, Ph.D. Professor of Chemical Engineering, Michigan Technological University Fellow, American Institute of Chemical Engineers (Section Editor, Process Safety Introduction, Combustion and Flammability Hazards, Gas Explosions, Vapor Cloud Explosions, Boiling-Liquid Expanding-Vapor Explosions)... 

Commonly used criteria includes SG-22, and CIA 1992. Both documents specify at least two blast overpressures for buildings spaced 100 feet (30 meters) from a vapor cloud explosion hazard as follows ... 

Although there is a wide range of explosions types, vapor cloud explosions are a primary concern in the petrochemical industry. Because there are no codes or industry standards for determining what blast overpressures should be used, the design blast loads are usually supplied by the facility owner. Considering the wide variety of processes, it is easy to understand why these overpressures will be different from one owner to the next and even for different locations within a single facility. Sonic owners have several hazard levels which are used to classify different plant arcas. These hazard levels are based on the material handled and the process used. 

Extra Hazard Units with light material, vapor cloud explosion potential, liquid inventory over 10,000 gal... 

Vapor forms explosive mixtures with air. Flammable limits, 3-17%. Flash point, 0°C. Ignition temperature, 481°C. Dilute solutions are also hazardous. Extinguish fires with water spray, dry chemical, foam, or carbon dioxide.2... 

When a large amount of volatile material is released rapidly to the atmosphere, a vapor cloud forms and disperses. If the cloud is ignited before it is diluted below its lower flammability limit, an uncontrolled vapor cloud explosion will occur. This is one of the most serious hazards in the process industries. Both shock waves and thermal radiation will result from the explosion, with the shock waves usually the more important damage producers. UVCEs usually are modeled by... 

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