Flammable/explosive energy

Flammable/explosive energy. If the pump handles hydrocarbons, or other materials that could ignite, they have to be cleared, often using an inert gas such as nitrogen. 

Risk analysis. The risk of accidents can be assessed in terms of two factors severity and probability of the accident. Severity is high if consequences of the accident to employees, the public, the environment, and the plant are significant. Severity is related to the amount and properties of hazardous (toxic, flammable, explosive) substances that can escape to the surroundings during the accident, and to the energy that is released during the accident. Probability is associated with the likelihood of the occurrence of unwanted chains of events and the time of development of undesired events starting from the disturbance. If the time... 

Risks linked with chemical processes are diverse. As already discussed, product risks include toxicity, flammability, explosion, corrosion, etc. but also include additional risks due to chemical reactivity. A process often uses conditions (temperature, pressure) that by themselves may present a risk and may lead to deviations that can generate critical effects. The plant equipment, including its control equipment, may also fail. Finally, since fine chemical processes are work-intensive, they may be subject to human error. All of these elements, that is, chemistry, energy, equipment, and operators and their interactions, constitute what we call process safety. 

The production of the process industry often involves hazards. Their nature can be both physical and chemical. Physical hazards derive from operating conditions which may be extreme, such as very low or very high temperatures and pressures. Chemical hazards are those associated with the materials present in the process, which can be toxic, flammable, explosible, or release energy due to spontaneous reactions. Indeed, it is the necessity to put the substances into a reactive state in order to enable one to produce the desired products that may lead to hazards. 

In addition to the hazards due to the toxic effects of chemicals, hazards due to flammability, explosibility, and reactivity need to be considered in risk assessment. These hazards are described in detail in the following sections. Further information can be found in Bretherick s Handbook of Reactive Chemical Hazards (Bretherick, 1990), an extensive compendium that is the basis for the lists of incompatible chemicals included in various reference works. Bretherick describes computational protocols that consider thermodynamic and kinetic parameters of a system to arrive at quantitative measures such as the Reaction Hazard Index (RHI). So-called "reactive" hazards arise when the release of energy from a chemical reaction occurs in quantities or at rates too great for the energy to be absorbed by the immediate environment of the reacting system, and material damage results. In addition, the "Letters to the Editor" column of Chemical Engineering News routinely reports incidents with explosive reaction mixtures or conditions. 

Designs should prevent and manage combustible and explosive mixtures in air. Particularly important are processes and operations where flammable mixtures of gases, vapors, and dusts with air can occur. This principle includes reducing oxidizers that add to the explosive energy of a combustible material. Fuel and oxidizers require separated storage. That is because of the increased risk when fuels and oxidizers are located adjacent to or near each other. 

Confined Explosions. Confined explosions occur when a flammable mixfure in a confined space is ignited. A typical example is the case of a flammable liquids tank. When these tanks are emptied, residu liquid may evaporate and form a flammable mixture in the tank. If ignited, a confined explosion would be produced. The modeling of confined explosion effects is analogous to the modeUng of BLEVEs. Here the explosion energy released is obtained from the enthalpy of combustion. 

In the absence of air, TEE disproportionates violently to give carbon and carbon tetrafluoride the same amount of energy is generated as in black powder explosions. This type of decomposition is initiated thermally and equipment hot spots must be avoided. The flammability limits of TEE are 14—43% it bums when mixed with air and forms explosive mixtures with air and oxygen. It can be stored in steel cylinders under controlled conditions inhibited with a suitable stabilizer. The oxygen content of the vapor phase should not exceed 10 ppm. Although TEE is nontoxic, it may be contaminated by highly toxic fluorocarbon compounds. 

Energy levels contributing to explosive effects (flammable releases)... 

Hybrid mixture A suspension of dust in air/vapor. Such mixtures may be flammable below the lower explosive limit of the vapor and can be ignited by low energy sparks. 

The violence of the confined explosions (flammable v apor, gas, and dust) can be calculaled by the e.xplosion pressme mid energy eqmitions introduced earlier. The behavior of flammability (or e.xplosivity) limits of flammable mixtures and dusts is also covered in preceding sections. 

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