3 Materials which are capable of detonation, but require a strong initiating source or which must be heated under confinement before initiation. Includes materials which are sensitive to thermal or mechanical shock at elevated temperatures and pressures. Also includes those materials which react explosively with water without heat or confinement. 4 Materials which in themselves are readily capable of detonation or explosive reaction at normal temperatures and pressures. Includes materials which are sensitive to mechanical or localized thermal shock.
Examples are materials that are capable of polymerization reactions, such as polyvinyl benzene.
Examples include the alkali metals and many hydrides. Examples include diethylzinc and triethylaluminum, and many organometallic compounds. Examples include peroxide forming materials and reactions involving explosive combinations of incompatible materials. The material is capable of detonation or violent reaction if subjected to a strong initiating force or heated under confinement. This includes all materials with an NFPA reactivity rating of 3, including those materials which are shock sensitive at elevated temperatures and pressures.