Chemical reaction hazards

The HSE is the body empowered to enforce the health and safety legislation in most factories. Via its local inspectors the HSE gives guidance on safe manufacmring practices, but initial enquiries should be addressed to the relevant trade association or professional body. 

This guide considers the hazards arising from uncontrolled exothermic activity. This can occur in the storage and handling of reactive substances, during the chemical reaction itself, or when the reaction products are being purified. 

Chemical reaction hazards are associated with thermal runaway, which begins when the heat generated by a reaction exceeds the heat which can be removed to the surroundings. The surplus heat increases the temperature of the reaction mass, which causes the reaction rate to increase and in turn accelerates the rate of heat production. Thermal runaway occurs because, as the temperature rises, the rate of heat loss to the surroundings increases linearly with temperature, but the rate of reaction — and so the rate of heat generation — increases exponentially. Therefore, thermal runaway can start slowly but then accelerate, until eventually it can lead to an explosion. 

A further problem is that the amount of heat produced increases in proportion to the volume of the reaction mixture (a cube term), whereas the cooling capacity varies in proportion to the surface area (a square term). This has critical implications for scale-up, where a small increase in volume may lead to inadequate cooling and loss of control. Experience indicates that this is not always fully appreciated. Incidents occur when processes are scaled up, having been carried out uneventfully for years at a slightly reduced scale. 

Where there is no thermal control, exothermic reactions will occur without significant heat loss (adiabatically). This will cause the temperature to rise to the maximum available This is calculated from  

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J. Barton and R. Rodgers, eds.. Chemical Reaction Hazards, Institution of Chemical Engineers, Rugby, Warwickshire, U.K., 1993, pp. 7—12. 

Controlling legionella m nursing and residential care homes Chemical reaction hazards and the risk of thermal runaway... 

Chemical reaction hazards must be considered in assessing whether a process can be operated safely on the manufacturing scale. Furthermore, the effect of scale-up is particularly important. A reaction, which is innocuous on the laboratory or pilot plant scale, can be disastrous in a full-scale manufacturing plant. For example, the heat release from a highly exothermic process, such as the reduction of an aromatic nitro compound, can be easily controlled in laboratory glassware. Flowever,... 

Barton, J. A. and Nolan, P. F. Incidents in the Chemical Industry due to Thermal-runaway Chemical Reactions, Hazards X Process... 

Barton, J. and Rogers, R., Chemical Reaction Hazards, 2nd ed.. Institution of Chemieal Engineers, 1997. 

Proceedings of Conference Technical for the Control and Prevention of Runaway Chemical Reaction Hazards, London Dec. 1987. 

Corrosion, See also Chemical reaction hazards causes, 54 preveutiou, 55... 

Evaluation of chemical reaction hazards Industrial partner Reference... 

Barton, J.A. and Nolan, P.F., 1991, in Safety in Chemical Batch Reactors and Storage Tanks , Benuzzi, A. and Zaldivar, J.M. (Eds.), Kluwer Academic Services, Dordrecht, pp. 99-124. Barton, J. and Rogers, R. (Eds.), 1993, Chemical Reaction Hazards - A Guide, Inst. Chem. Engrs., Rugby. 

Rogers, R.L., 1989, The Systematic Asse.ssment of Chemical Reaction Hazards , Imperial Chemical Industries, Fine Chemicals Manufacturing Organisation, Blackley. 

Development Chemistry— Characterization of materials Characterization of process alternatives Choice of process Suitability of process Screening for chemical reaction hazards... 

Pilot Plant—Chemical reaction hazards Influence of plant selection on hazards Definition of safe procedures Effects of expected variations in process conditions Definition of critical limits... 

Full Scale Production—Reevaluation of chemical reaction hazards Newly revealed reactivity hazards from plant operations Management of changes Update of safety procedures as required Ongoing interaction of process safety with engineering, production, economic, andcommercial aspects of the process... 

During full scale production, particularly initially, chemical reaction hazards may be reevaluated. More tests may be necessary as a consequence of increased knowledge of the process, changed production requirements, or other process changes such as the use of different feed stocks. 

Gibson, N., "Hazard Evaluation and Process Design," in Proceedings of Runaway Chemical Reaction Hazards Symposium, IBC, London, England (1987). 

Bretherick, L., "Chemicals, Reactions, Hazards," in Safety Loss Prevention in Chem. Oil Processing Ind. Symposium, D5 (1989), Singapore. 

Stull, D. R., "Identifying Chemical Reaction Hazards," CEP Technical Manual, Loss Prevention, 4,16 (1970), American Institute of Chemical Engineers, New York, NY. 

Guidelines for Chemical Reaction Hazard Evaluation, The Association of the British Pharmaceutical Industry, London, England (1989). 

Rogers, R. L., "DEWAR Methods for Evaluating Chemical Reaction Hazards," DECHEMA Tagung, Bad Soden, Germany (1990). 

Historical perspective An analysis of thermal runaways in the United Kingdom (Barton and Nolan, Incidents in the Chemical Industry due to Thermal Bunaway Chemical Reactions, Hazards X Process Safety in Fine and Specialty Chemical Plants, IChem 115 3-18) indicated that such incidents occur because of the following general causes ... 

Interaction matrix A two-dimensional matrix listing all components of interest on the x and y axes and recording the consequences of mixing of these components for each combination of the components. It is useful for identifying chemical reaction hazards and incompatibilities. 

Designing and Operating Safe Chemical Reaction Processes (HSE 2000). Published by the U.K. Health and Safety Executive and directed to small to medium-sized chemical manufacturing companies using batch and semi-batch processes. It addresses chemical reaction hazards and inherently safer processes, hazards assessment, preventive and protective measures, and management practices. 

When previous chemical reactivity incidents have been examined, particularly where established instructions were not followed, it is often found that facility personnel did not know that violating the procedure could lead to an uncontrolled reaction. Knowledge of the chemical reaction hazards would make procedural violations less likely. 

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