Hazard data, estimation, CHETAH

CHETAH is a tool for the preliminary screening of the reactivity hazards of organic chemicals. The evaluation is based on pattern recognition techniques using experimental hazard data and estimated thermochemical data. 

A well-known tool for the estimation of reactivity hazards of organic material is called CHETAH [5]. The method is based on pattern recognition techniques, based on experimental data, in order to infer the decomposition products that maximize the decomposition energy, and then performs thermochemical calculations based on the Benson group increments mentioned above. Thus, the calculations are valid for the gas phase, but this may be a drawback, since in fine chemistry most reactions are performed in the condensed phase. Corrections must be made, but in general they remain small and do not significantly affect the results. 

In summary, we would like to emphasize the two current capabilities of the CHETAH program. The first is the estimation of gas phase thermodynamic data over the range of 25-1200°C, using Benson s second order group contribution method. The second capability of CHETAH is a hazard appraisal. This uses thermodynamic data to... 

Copies of the TNO peroxide test databases have been provided to E27.07 and the new versions of CHETAH are expected to contain an extensive database as well as pattern-recognition techniques for estimating the hazard of new materials. The CHETAH software will continue to rely on bond energy data and group contribution calculations to estimate energy release potential. Hopefully, the new versions will also incorporate natural language expert system-type front ends so that the CHETAH program(s) will see expanded use in both analytical and tutorial modes. Copies of the LEILA (8) dissertation have also been provided to E27.07 as an example of an expert system approach to selection and use of appropriate theories and computational methods for the solution of problems in chemical kinetics. 

All the thermodynamic calculations performed by CHETAH are for species in the gas phase. Since most chemical processing is carried out in the condensed phase this may seem a weakness. However, in most cases the deviations from the condensed phase values are either too small to affect the result significantly or can be estimated by other means. Also, the correlations used in the hazard evaluation section of the program are based on experimental data for condensed phase species. 

Frurip, D.J., Freedman, E. and Hertel. G.R.. 1989, A new release of the ASTM CHETAH programme for hazard evaluation versions for mainframe and personal computer, Int Symp on Runaway Reactions. 39-51 (CCPS, AIChE, USA). Benson. S.W., 1976, Thermochemical Kinetics. Methods for the Estimation of Thermochemical Data and Rate Parameters. 2nd edition (Wiley). 

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