Vapor control, spills

Spills and Disposal Procedures. If a spiU occurs outdoors, personnel should stay upwind of it. If the spiU is in a diked area it may be possible to recover much of the bromine, otherwise it should be absorbed with appropriate material. A water spray can be used to control bromine vapors and a mild ammonia atmosphere helps to neutralize bromine vapors. Small spills may be neutralized with lime water slurry or soda ash and flushed with large amounts of cold water. 

SPILL CLEAN UP use water spray to cool and disperse vapors dilute spills to form nonflammable mixtures control runoff and isolate discharged material for proper disposal eliminate all ignition sources. 

SPILL CLEAN-UP use water fog or spray to knock down and absorb vapors control runoff and properly dispose of discharge material. 

Large Fans These could be used to dilute a vapor cloud below its LFL with ambient air (see, for example, Whiting and Shaffer, Feasi-bihty Study of Hazardous Vapor Amelioration Techniques, Proc. 1978 Nat. Conf. on Control of Hazardous Material Spills, USEPA, Miami Beach, April 1978). But caution must be exercised because the turbulence produced by fans will likely promote rapid combustion and a resulting UVCE unless vapors are diluted below the LFL. Nevertheless, in new plants, strategic placement of air coolers may provide enough air flow to reduce the risk of a UVCE. 

Install flame arresters on atmospheric vents to prevent fire on the outside of the tank from propagating back into the vapor space inside the tank. Provide fire resistant insulation for critical vessels, piping, outlet valves on tanks, valve actuators, instruments lines, and key electrical facilities. Provide remote controlled, automatic, and fire-actuated valves to stop loss of tank contents during an emergency provide fire protection to these valves. Valves should be close-coupled to the tank, and must be resistant to corrosion or other deleterious effects of spilled fluids. Vessels should be provided with overpressure relief protection. 

Material stored at or below its atmospheric pressure boiling point has no superheat. Therefore there will be no initial flash of liquid to vapor in case of a leak. Vaporization will be controlled by the evaporation rate from the pool formed by the leak. This rate can be minimized by the design of the containment dike, for example, by minimizing the surface area of the liquid spilled into the dike area, or by using insulating concrete dike sides and floors. Because the spilled material is cold, vaporization from the pool will be further reduced. 

Accidental vapor cloud explosions do not occur under controlled conditions. Various experimental programs have been carried out simulating real accidents. Quantities of fuel were spilled, dispersed by natural mechanisms, and ignited. Full-scale experiments on flame propagation in fuel-air clouds are extremely laborious and expensive, so only a few such experiments have been conducted. 

Spill/Leak Disposal Isolate the incident scene dress in proper personal protective equipment (see above) do not allow contact with any materials, liquid or gas stop and/or control leak or hazard if possible to do so and control water - use water spray to control vapor and any vapor cloud. Contain product and keep phosgene from entering sewers, streams, or water intakes. Dike surface flow, and depending on the temperature, try to neutralize the product for disposal using agricultural lime (slaked lime), crushed limestone, or soda ash, or sodium bicarbonate. 

This section includes guidelines for the central control station equipment, emergency alarm stations, supervisory devices, and visual and audible alarm services. These systems can be used for all types of in-house emergencies, such as fires, explosions, vapor releases, liquid spills, and injuries. 

Most combustible liquids do not present a vapor problem if accidentally released into the atmosphere. The probability of a fire, therefore, is considerably less than it would be if the spill was of a flammable material. If, however, the combustible liquid is at a temperature higher than its flashpoint, then it can be expected to behave in the identical manner a flammable liquid. One major difference between the two in a fire situation is that the potential exists for cooling the combustible liquid below its flash point by the proper application of water (generally applied in the form of water spray). In the event the liquid is burning, and if the fire forces are successful in achieving the required reduction in liquid temperature, then vapor production will cease and the fire will be extinguished because of a lack of vapor fuel. Unless this reduction in liquid temperature can be brought about, the fire will necessitate the same control considerations a low-flash liquid fire would. 

The effectiveness of dilution is highly chemical-specific and must be well conceived and tested. For instance, the improper addition of another material to a spill could cause the rapid evolution of heat, which could accelerate the evaporation rate and make the situation worse. Even with the proper diluent selection, the method and rate of addition are both important for controlling vapor evaporation rates. If water is to be used as a diluent for a material with a high heat of dilution, such as sulfuric acid or oleum, it must be added rapidly and in a large enough quantity to not only effect the dilution, but also serve as a heat sink for the heat of dilution produced. In this way, high evaporation rates for the pool being diluted will be minimized. 

Greer, J. S., and S. S. Gross. 1980. The Practicality of Controlling Vapor Released from Spills of Volatile Chemicals through Cooling Control of Hazardous Material Spills. Proceedings of National Conference, pp. 130-133. Nashville, TN Vanderbilt University. 

As discussed in Section 3.1.2.1, a liquid that is uncontained is one over which there is no control and which will result in potentially severe consequences. If a dike is placed around the tank containing the refrigerated liquid ammonia and the ammonia spill is confined within it, a much reduced hazard zone can be obtained because we have limited the surface area available for vaporization and additional postrelease mitigation measures can be applied. As pointed out in Chapter 3, combinations of postrelease mitigation measures will provide the best overall response to an accidental release. 

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