Chemical compatibility, reactivity hazards

Up to this point, the chemical reactivity hazards of individual substances, either by themselves or in contact with common environmental materials, have been considered. This last question in the chemical reactivity hazards screening will address the potential for an unintended chemical reaction due to incompatible materials contacting each other. Compatibility, in this context, means the ability of materials to exist in contact without specified (usually hazardous) consequences under a defined scenario. A scenario, in this context, is a detailed physical description of the process whereby a potential inadvertent combination of materials may occur (ASTM E 2012-00). 

Therefore, chemical reactivity is not necessarily an intrinsic property of a single chemical substance. The severity of reactive hazards is influenced by process-specific factors, such as operating temperatures, pressures, quantities handled, chemical concentrations, impurities with catalytic effects, and compatibility with other chemicals onsite. 

The American Society for Testing and Materials (ASTM) is a not-for-profit organization that provides a forum for the development and publication of voluntary consensus standards for materials, products, systems, and services.67 One ASTM committee (E27) develops standardized physical and chemical test methods on the hazard potential of chemicals, including but not limited to reactive hazards. The committee has developed standard analytical methods for calorimetry studies in addition to a standard guide for determining binary chemical compatibility (ASTM, 2000). 

Completing a compatibility chart often requires persistence and determination. You or someone in your organization may be able to readily answer whether most combinations are reactive or not. A few combinations may take more work. One way to do a quick check on chemical combinations is to use a method such as the Chemical Reactivity Worksheet, available free of charge (see the Where Can We Get More Help section of this document under Reactive Interactions). This program has over 6,000 chemicals in its database, and predicts the results of two-chemical mixtures by reactive group combinations. The Worksheet not only indicates possible hazardous interactions, it also sets up a compatibility chart and indicates potential consequences of the interactions (e.g., Heat generation by chemical reaction, may cause pressurization ). 

NFPA developed Standard 704 as a tool for identification and evaluation of potential hazards during emergency response, not for application to chemical process safety. The instability rating is a part of this standard. It was not intended to be used to measure reactivity, but rather to measure the inherent instability of a pure substance or product under conditions expected for product storage. The instability rating does not measure the tendency of a substance or compound to react with other substances or any other process-specific factors, such as operating temperature, pressure, quantity handled, chemical concentration, impurities with catalytic effects, and compatibility with other chemicals onsite. 

Compatibility of Explosives with other Substances The term compatibility refers almost exclusively to chemical reactivity between materials, that is, the ability of a given expl to exist unchanged under certain conditions of temp moisture, when in the presence of some other material. If this condition exists, the two materials are said to be compatible. Incompatibility of an expl and another material in which it may be in contact may result in loss of effectiveness of the expl, or it may result in extreme hazard... 

Primary expls are the most sensitive of all chemical components in military ammo and hence the most hazardous to handle. Furthermore, single component primary expls are frequently too hazardous to handle and mixts are often used. Before the components of such a mixt are blended, the sensitivity, stability and compatibility must be tested. Reactivity increases with decreasing particle size and increasing intimacy of contact. Because primary expls are so sensitive, not more than 0.5g should be prepd initially. If a compd forms a filter... 

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