Dispersion hazards

Consequence Analysis the effects of the in the plant on the workers and the dispersed hazardous materials on the publie and environment is assessed using computer models,... 

The heat of reaction can cause thermal burns, ignite combustible materials, or initiate other chemical reactions. Flammable, corrosive or toxic gases are often formed as reaction products. The violence of some reactions may disperse hazardous materials. Even slow reactions can generate sufficient heat and off-gases to overpressurize and rupture a closed container. 

Dilwali, K. M and K. S. Mudan. 1987. Dike Design Alternatives to Reduce Toxic Vapor Dispersion Hazards. Paper presented at the AIChE Vapor Cloud Conference Proceedings, Boston, MA. New York American Institute of Chemical Engineers. 

If the heat transfer loop is at pressures in excess of the chemical plant, the compressed heat transfer fluid becomes an energy source to disperse hazardous chemicals if a heat exchanger fails. The chemical industry has traditionally used low pressure, low-energetic liquids as heat transfer agents to avoid this type of accident. This has included various molten salts in traditional applications to 600 C. Several chemical companies, such as DOW, produce specialized heat transfer liquids for these applications. Because there has not been a demand, molten salt heat transfer agents for very high temperatures have not been developed or commercialized. 

High-pressure helium has not been used for safety, performance, and cost reasons. If helium is allowed, active safety systems with very fast acting valves dumping to atmosphere will be required for rapid depressurization in the event of an accident before the chemical plant is pressurized and disperses hazardous chemicals. 

When dispersed as a dust, adipic acid is subject to normal dust explosion hazards. See Table 3 for ignition properties of such dust—air mixtures. The material is an irritant, especially upon contact with the mucous membranes. Thus protective goggles or face shields should be worn when handling the material. Prolonged contact with the skin should also be avoided. Eye wash fountains, showers, and washing faciUties should be provided in work areas. However, MSDS Sheet400 (5) reports that no acute or chronic effects have been observed. 

Both functional and decorative coatings can be appHed to paper from latices. The aqueous dispersions can be used on conventional paper converting machinery which usually cannot handle hot melts and solvent coatings. The lack of fire hazard because of absence of solvents is an added advantage of the latex system. 

Flammability = 4, ie, very flammable gas, very volatile, and materials that in the form of dusts or mists form explosive mixtures when dispersed in air Health = 2, ie, hazardous to health, but may be entered freely with self-contained breathing apparatus Reactivity = 0, ie, is normally stable when under fire-exposure conditions and is not reactive with water... 

Dust Explosions Static Electricity Hazards of Vacuum Hazards of Inert Gases Gas Dispersion... 

When considering release scenarios, the most hazardous unit in a plant should be chosen, based on inventoiy and process conditions. The idea is to imagine the release of material in the fastest way that is reasonably possible. The worst realistic scenario should be considered. This can be based on the outcome of a review, from a HAZOP study or a hazard analysis. The time a scenario will take is almost always considered to be continuous, because after a few minutes a stable dispersion distance exists. Making the time longer will not necessarily change the hazard distance. 

Example The combustion process in large vapor clouds is not known completely and studies are in progress to improve understanding of this important subject. Special study is usually needed to assess the hazard of a large vapor release or to investigate a UVCE. The TNT equivalent method is used in this example other methods have been proposed. Whatever the method used for dispersion and pressure development, a check should be made to determine if any govern-mentaf unit requires a specific type of analysis. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

Hot gases rise by thermal lift. Henee in the open air they will disperse. Within buildings this is a serious eause of fire esealation and toxie/asphyxiation hazards if smoke and hot gases are able to spread without restrietion (or venting) to upper levels. 

All eombustible solids ean ereate a dust explosion hazard if dispersed in air as a fine dust within eertain eoneentration limits. Refer to Table 6.2. The hazard inereases with deereasing partiele size. 

Hazardous chemicals or mixtures may be replaceable by safer materials. These may be less toxic per se, or less easily dispersed (e.g. less volatile or dusty). Substitution is also applicable to synthesis routes to avoid the use of toxic reactants/solvents or the production, either intentionally or accidentally, of toxic intermediates, by-products or wastes. 

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