Runaway reactions consequences

Accelerating Rate Calorimeter (ARC) The ARC can provide extremely useful and valuable data. This equipment determines the self-heating rate of a chemical under near-adiabatic conditions. It usu-aUy gives a conservative estimate of the conditions for and consequences of a runaway reaction. Pressure and rate data from the ARC may sometimes be used for pressure vessel emergency relief design. Activation energy, heat of reaction, and approximate reaction order can usually be determined. For multiphase reactions, agitation can be provided. 

Determine consequences of runaway reactions and ensure mitigation techniques are in place... 

Low temperatures can cause a phase separation in stabilized solutions in which case one phase can become deficient in stabilizer and subject to runaway reactions. Acrylic acid can crystallize out of stabilized solution, and subsequent thawing of these essentially pure acrylic acid crystals can initiate runaway reactions, often with severe consequences. Thawing of crystallized (frozen) materials needs to be accomplished using established procedures in thaw boxes or similar devices. If established procedures are not available, a safety review needs to be conducted and a procedure developed prior to thawing the material. 

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. 

The MIC storage tank was contaminated by substantial quantities of water and chloroform—up to a ton of water an VA tons of chloroform— and this led to a complex series of runaway reaction [4]. The precise route by which water entered the tank is unknown several theories have been put forward, and sabotage seems the most likely [2], though whoever deliberately added the water may not have realized how serious the consequences would be. Hazard and operability studies (Section 18.7) are a powerful tool for identifying ways in which contamination and other... 

Most of the chemical reactions in the process industry are temperature dependent. They are either exothermic or endothermic. As a consequence, it is often necessary to remove the heat generated by an exothermic reaction to control the reaction temperature and to avoid thermal runaway reactions or to suppress endothermic by-product reactions, for instance [8]. 

The root cause of this accident was poor operating procedures and poor process infoiv mation. The operating procedure, for example, did not cover the safety consequences of deviations from the normal operating conditions, such as the possibility of a runaway reaction and the specific steps to be taken to avoid or recover from such deviations. 

Consequence of runaway reaction Temperature rise rates Gas evolution rates Adiabatic Dewar Adiabatic calorimetry Pressure ARC VSP/RSST RC1 pressure vessel... 

On April 8,1998, at 20 18, an explosion and fire occurred during the production of Automate Yellow 96 Dye at Morton International, Inc. Yellow 96 dye was produced by mixing and reacting two chemicals, ortho-nitrochlorobenzene (o-NCB) and 2-ethylhexylamine (2-EHA). The explosion and fire were the consequence of a runaway reaction, which overpressurized a 2000-gal capacity chemical reactor vessel and released flammable material that ignited. Nine employees were injured, including two seriously, and potentially hazardous materials were released into... 

Understanding the consequences of runaway reactions or toxic gas evolution. 

The additional measures can be divided into preventive measures to prevent an uncontrolled reaction and design measures to mitigate unacceptable consequences of a runaway reaction. Depending on the circumstances of each individual case the following alternatives or a combination thereof can be considered ... 

Pressure resistant construction or equipment protected by pressure relief devices are considered highly reliable where design measures are adopted to prevent unacceptable consequences of a runaway reaction. Design measures, especially the provision of pressure relief, may be appropriate and also required when a complete and reliable evaluation of deviations, their causes and consequences cannot be achieved. This can happen as a result of the complexity of the contributing causal chains. 

In both the OSHA PSM Standard and the EPA RMP regulation, the PHA element does not currently specify the factors that must be considered to effectively manage reactive hazards. Present requirements should be augmented to explicitly require an evaluation of such factors as rate and quantity of heat generated maximum operating temperature to avoid decomposition thermostability of reactants, reaction mixtures, byproduct waste streams, and products effect of charging rates, catalyst addition, and possible contaminants and understanding the consequences of runaway reactions or toxic gas evolution. 

Effect of variables such as charging rates, catalyst addition, and possible contaminants. Understanding the consequences of runaway reactions or toxic gas evolution. 

Adiabatic calorimetry Chemical testing technique that determines the self-heating rate and pressure data of a chemical under near-adiabatic conditions. ( Adiabatic refers to any change in which there is no gain or loss of heat.) This measurement technique conservatively estimates the conditions for, and consequences of, a runaway reaction. 

Consequently, it is normally recommended that the relief pressure be chosen as low as possible. This needs to be balanced with the need to provide a suitable margin between the set pressure or minimum specified bursting pressure and.the highest normal operating pressure so that spurious operation of the relief device is avoided. (Manufacturers of relief devices can advise on this.) Also, in some cases, it may be beneficial to set a high relief pressure where a first runaway reaction can be contained, but a subsequent slow decomposition reaction (at. higher temperature) must be vented. 

Protective measures mitigate the consequences of a runaway reaction. They are rarely used on their own, as some preventive measures are usually jxesent to reduce the demand on the protective system. The main options are ... 

The small-scale test (see A2.4)i which measures dT/dt, and hence q, for the.runaway reaction must be performed in a way which simulates the same external heating rate as for the full-scale reactor. This is to ensure that a safe value of q is obtained. If the small-scale test was not also externally heated, the relief pressure would be reached at a higher reactant conversion and consequent lower reaction rate, than in the full scale vessel with external heat input. It should also be noted that, as there is no mass loss in the small-scale test, the whole initial mass of reactants, mR, rather than mR/2 can be used in the calculation of the rate of temperature rise due to external... 

A publication summarises all the then available technical evidence related to the Seveso accident, and recommends operational criteria to ensure safety in commercial processes to produce trichlorophenol [4]. All the plant scale incidents were characterised [1] by the subsequent occurrence of chloracne arising from the extremely toxic and dermatitic compound 2,3,7,8-tetrachlorodibenzodioxin, formed during the thermal runaway reaction and dispersed in the ensuing explosion. It is also extremely resistant to normal chemical decontamination procedures, and after the 1968 explosion, further cases occurred after transient contact with plant which had been decontaminated and allowed to weather for 3 years, and which appeared free of dioxin [7,9]. The consequences at Seveso 447 cases of chemical burns (NaOH) and 179 of chloracne, only 34 with both [17],... 

The thermal risk linked to a chemical reaction is the risk of loss of control of the reaction and associated consequences (e.g. triggering a runaway reaction). Therefore, it is necessary to understand how a reaction can switch from its normal course to a runaway condition. In order to make this assessment, the theory of thermal explosion (see Chapter 2) needs to be understood, along with the concepts of risk assessment. This implies that an incident scenario was identified and described, with its triggering conditions and the resulting consequences, in order to assess the severity and probability of occurrence. For thermal risks, the worst case will be to lose the cooling of a reactor or in general to consider that the reaction mass or the substance to be assessed is submitted to adiabatic conditions. Hence, we consider a cooling failure scenario. 

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