Identifying criteria to classify chemical mixtures as "highly hazardous" due to chemical reactivity

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This paper uses 13 sets of calorimeter data to evaluate a number of common criteria to characterize chemical reactive hazards. The purpose is to "brainstorm" whether a criterion or set of criteria can be used to trigger PSM or RMP requirements for reactive chemicals. Such a criterion must be cost-effective, easy to use, and, ideally, should not rely on additional experimental testing. A total of 12 criteria were considered in this work: NFPA instability rating, experimental heat of reaction, experimental total heat release, instantaneous power density (IPD), reaction onset temperature, total change in temperature, total change in pressure, maximum temperature rate, maximum pressure rate, CHETAH predicted energy, and the Melhem Index (based on the calculated heat of reaction at the equilibrium state, and the computed adiabatic reaction temperature (CART)). Screening values, mostly selected arbitrarily, were assigned to the criteria. Based on this very limited set of calorimeter data, the following conclusions can be made: • No single criterion is likely to be adequate for screening all classes of reactive chemicals. • The calculated heat of reaction performed "best" as a single parameter, screening 10 of the 13 systems (77%) using a 100 cal/g threshold. If the pure material is used (without solvent), then the calculated heat of reaction screens 12 of the 13 systems. • The total pressure increase screened 61% of the data sets and experimental heat release screened 54%. Combined, the two criteria screened 77% of the chemicals. • The NFPA instability rating combined with the calculated heat of reaction screened 12 of the 13 systems (92%). Adding the total pressure change screened all of the systems (100%), although adding the pressure change requires closed-cell calorimeter data. • The Melhem Index does not screen any additional chemicals over the calculated heat of reaction by itself. However, the hazard class of two systems is increased from LOW to INTERMEDIATE by the addition of the CART vFalues. • Most of the criteria require experimental data. Many require data from an adiabatic, closed-cell calorimeter. • The results of this study are mixed. It might be possible to establish a screening method based on several of the criteria discussed in this paper. However, this would require much more analysis with a much larger set of chemicals prior to establishing a final screening method. © 2003 AIChE. Published by Elsevier Ltd. All rights reserved.

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Journal of Loss Prevention in the Process Industries