Vapor hazards, explosives facilities

In explosive facilities and locations where the atmosphere may contain combustible dusts, or flammable vapors or gases, ferrous metal surfaces should not be coated with aluminum paint due to the potential sparking hazard. 

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. 

A corrosion issue is possible at telephone facilities that have backup facilities that use diesel fuel generators supplied by USTs. Leaking UST systems can contaminate groundwater supplies and can cause fires, explosions, and vapor hazards. The USTs... 

Different materials pose different hazards, including thermal radiation, explosion overpressure, and toxic and flammable vapor clouds. Some materials pose only one hazard, while others may pose all four. For the purposes of ranking facilities you will need to estimate the laigest area affected by the potential hazards. You can arrive at such an estimate by calculating the greatest downwind distance to a particular level of hazatd. The following thresholds are commonly applied ... 

Facilities can be ranked based on the sum of the maximum hazard distances for each release. Only one hazard distance should be used for each release, even if there is the potential for more than one hazard (thermal radiation, explosion overpressure, toxic cloud and flammable vapor cloud). The highest-ranked facility will be the one whose potential releases would reach the greatest total distance. 

Repair and Reuse After Explosion. Although the risk of a high order detonation of a munition during disassembly is low, this hazard does exist. In the event of such an incident, it is a design requirement for the containment rooms to suffer only minimal damage and allow rapid refurbishment. To assure this capability, the containment room structural design criteria are more conservative than Department of Defense Explosive Safety Criteria would normally require. This is considered appropriate since vapor containment is so critical in this facility. 

Vapor or Dust. Once the hazardous elements for each process within the facility have been identified, it is necessary to determine whether they constitute a hazard due to being a vapor or a dust. Vapor and dust represent two different types of explosion hazards. 

Generation of combustible vapors is a hazard not only for the storage of pure flammable liquids but also for the storage of any sludge or mixture where a combustible component is present or can be produced by reaction. Sludge (slop tanks) and mixture (e.g., oil/water) tanks may be particularly vulnerable because they are sometimes open to the air explosive atmospheres may form inside and outside the tank. Facilities may not always recognize the hazard. In addition, even tanks appearing to be empty may pose a hazard if they still contain combustible vapors. 

Neutralization or Demilitarization Hazardous items may be neutralized by detonation in place, or they may be removed to a demilitarization facility located on, or at some distance from, the site undergoing remediation. Detonation in place, which is often the only safe method for neutralization of explosive items, carries with it concerns for blast, noise, and vapor containment. Blast containment coverings tend to be heavy, bulky, and difficult to position. Sand tamping for noise control is labor intensive and time consuming, and it creates problems with dust. Reliable mathematical models for predicting the noise impact on neighboring communities do not appear to be available, although their development should not be particularly difficult. 

Two major hazards may occur from high pressure vessel failures. The vessel itself may rupture and the formation of vapor cloud as a result of the rupture is possible. If the vessel ruptures, it will produce flying projectiles and usually release large quantities of vapors, and in the case of most hydrocarbons are combustible.The projectiles could harm individuals or damage the process facility, possibly increasing the incident proportions. Secondly, the release of a combustible gas from a pressurized vessel may cause the formation of combustible vapor cloud, which if a suitable amount of congestion is present or some turbulence of the cloud occurs, an explosive blast may result once the cloud contacts an ignition source. 

In this research, physical effects of the reference scenarios were calculated using ALOHAS one of the widely accepted atmospheric dispersion model used for evaluating releases of hazardous chemical vapors, including toxic gas clouds, fires, and explosions. For calculation purpose, we used data about the hazardous facilities, as obtained from the RMIS database and the most frequently occurring atmospheric condition with an average wind speed of 3.0 m/s, 35°C temperature and stability class of D as input parameters. 

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