Hydrocarbon fires process system explosions

Ideally most oil or gas incidents will be controlled by the process shut down systems (ESD, depressurization, drainage, etc.) and hopeful the fire protection systems (fireproofing, water deluge, etc ), will not be required. However these primary fire defense systems may not be able to control fire incidents if previous explosions have previously occurred. Before any consideration of fire suppression efforts, explosion effects must first be analyzed to determine the extent of protection necessary. Most major fire incidents associated with hydrocarbon process incidents are preceded by explosion incident. 

Hydrocarbon processing facilities pose severe risks with respect to fire, explosions and vessel ruptures. Among the prime methods to prevent and limit the loss potential from such incidents are the provisions of hydrocarbon inventory isolation and removal system. These systems are commonly referred to in the petroleum industry as ESD (emergency shutdown) and depressuring or blowdown. Although most standards and practices acknowledge the need for depressuring capabilities the exact determination of their requirement is not wholly defined. NFPA fire codes and standards rarely mention the subject. 

The other common source of process releases is leakage. Contained hydrocarbons will not bum unless an oxidizer is available, but once a leak is present adequate oxygen supplies are immediately available from the air. To prevent explosions and fires the integrity of the plant must always be kept at its highest and introduction of air supplies to closed systems must be eliminated. 

The most destructive incidents in the petroleum and related industries are usually initiated by an explosive blast that can damage and destroy unprotected facilities. These blasts have been commonly equated with the force of a TNT explosion and are quite literally like a bomb. The protection of hydrocarbon and chemical industries is in a rather unique discipline by itself, which requires specialized techniques of mitigation and protection in a systems based approach. The first step in this process is to understand the characteristic of hydrocarbon releases, fires, and explosions. 

Sharing of past major incidents with other oil and gas industries provides useful input data for similar process industries in order to identify the most critical barriers and improve their safety processes. One poignant example highlights this matter. In 1998 there was an accident in the gas compression stage of a Middle East oil and gas plant which caused 7 dead as a result of fuel accumulation and vapor cloud explosion which was very similar to the Texas City Refinery disaster on March 23, 2005 in which a distillation tower was overfilled and an uncontrolled release of hydrocarbons led to a major explosion and fires. Fifteen people were killed and 180 were injured in the worst disaster in the United States in a decade. In both incidents, excess hydrocarbons were diverted into a pressure relief system that included a blowdown stack. In the Iranian case, it was equipped with a flare, but one which the operator didn t ignite in Texas City the blowdown stack was not equipped with a flare to burn off hydrocarbons as they were released. As a result, the flammable overflow from the tower entered the atmosphere. Ignition of the escaped hydrocarbons was enabled by startup of a nearby vehicle resulted in the explosion and subsequent fires (Hopkins, 2008). This example shows the repetitive patterns of accidents, and root causes of events all over the world in this sector. The lesson of this paper is that accidents in one country, where the scenarios are very similar, can and should serve as lessons to prevent the same scenario being actualized in other countries. 

In hazardous industries, human actions may determine whether a major accident can be avoided or not. In this Section, we will look closer into the role of the operators in the control of major accidents. We have in Chapter 7 identified the different barriers applied in the prevention of fires and explosions in a plant for processing of hydrocarbons. They represent an engineering solution, based on the defences-in-depth philosophy. The idea is to minimise the system s vulnerability to human and technical errors by providing independent and diverse layers of protection. Whereas the operator has a distinct role in maintaining production, the safety systems will take over in cases where the system transgresses certain defined limits. There are many examples, however, where these different barriers are dependent on and vulnerable to operator actions. 

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