Evaluating chemical reaction hazards

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

IChemE acknowledges that there is no standard procedure for evaluating chemical reaction hazards (Barton and Rogers, 1997 p. 120). The CSB survey further highlights the variety of approaches to reactive hazard evaluation companies rely to varying degrees on quantitative and qualitative evaluation methods. 

There is no standard procedure for evaluating chemical reaction hazards. Evaluation must correlate with both the stage of process development — lab-scale, pilot plant, full-scale manufacture or modifications — and the degree to which the process has been defined. Figure 3.1 shows a typical evaluation procedure. Another example of a procedure is the one developed by the Association of the British Pharmaceutical Industry for the pharmaceutical industry. The main procedures include ... 

Evaluation of chemical reaction hazards Industrial partner Reference... 

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

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

Leggett, D.J. 2002. "Chemical Reaction Hazard Identification and Evaluation Taking the First Steps." AIChE Loss Prevention Symposium, New Orleans. March. 

The evaluation of chemical reaction hazards involves establishing exothermic activity and/or gas evolution that could give rise to incidents. However, such evaluation cannot be carried out in isolation or by some simple sequence of testing. The techniques employed and the results obtained need to simulate large-scale plant behavior. Adiabatic calorimeters can be used to measure the temperature time curve of selfheating and the induction time of thermal explosions. The pertinent experimental parameters, which allow the data to be determined under specified conditions, can be used to simulate plant situations. 

The evaluation of the potential hazards associated with chemical processes and plant operational procedures is a specialised activity. In larger companies a separate group will be responsible for this activity. The work involves testing for any fire and explosion hazards associated with the chemicals and the reaction mass in which they are produced, known as the chemical reaction hazards. The process details are considered in relation to the actual chemical plant in which they are to be operated the plant operational hazards. 

To ensure safety at the laboratoiy scale it is usually sufficient for a responsible chemist to ensure that the materials being handled will not detonate or deflagrate and that the process does not involve a violently exothermic reaction. However, a more detailed evaluation of the potential chemical reaction hazards is often valuable at this stage to aid in route selection and process development. 

Chemical reaction hazards should be assessed by technically-qualified personnel who have some experience of hazards evaluation and a good knowledge of the chemistry of the process. They should also be familiar with the plant to be used. Ideally the hazard assessors should be part of an independent team, to avoid conflict of interest between production and safety. 

In considering the hazards which may arise in a chemical process, it is not sufficient to evaluate the process chemistry alone. Chemical reaction hazards are closely interrelated with the operating conditions and plant used. For safe manufacturing it is also necessary to specify suitable safety measures and to ensure that they are implemented and maintained. (See also case histories Al 1-14, pages 162-165.)... 

Process definition is considered further in this chapter and the general hazards of plant operation are considered in Chapter 7. Chapters 3,4 and 5 cover the evaluation of chemical reaction hazards and the effect of process maloperations. The selection of safety measures is the subject of Chapter 6. Chapter 8 covers the implementation and maintenance of safety measures. 

The procedure used to evaluate the chemical reaction hazards was as... 

The editors hope that this second edition will provide a basis for the identification and evaluation of chemical reaction hazards not only for practising chemists, engineers and plant personnel but also for students, upon whose understanding and knowledge safety in the future rests. 

Small concentrations of volatile components in a liquid mixture may accumulate in the vapor space of a container over time and appreciably reduce the flash point relative to the reported closed-cup value. This may be the result of degassing, chemical reaction or other mechanism. An example is bitumen [162]. Similarly, if a tank truck is not cleaned between deliveries of gasoline and a high flash point liquid such as kerosene or diesel oil, the mixture might generate a flammable atmosphere both in the tmck tank and the receiving tank. Contamination at the thousand ppm level may create hazards (5-1.4.3 and 5-2.5.4). Solids containing upward of about 0.2 wt% flammable solvent need to be evaluated for flammable vapor formation in containers (6-1.3.2). 

The SIMULAR, developed by Hazard Evaluation Laboratory Ltd., is a chemical reactor control and data acquisition system. It can also perform calorimetry measurements and be employed to investigate chemical reaction and unit operations such as mixing, blending, crystallization, and distillation. Ligure 12-24 shows a schematic detail of the SIMULAR, and Ligure 12-25 illustrates the SIMULAR reaction calorimeter with computer controlled solids addition. 

Brogli, F., 1982, OYEZ Symposium Evaluation of Thermic Hazards and Prevention of Runaway of Chemical Reactions , Zurich. 

---