Definition - What does Reactivity mean?
Reactivity, in the context of occupational health and safety, refers to a substance's tendency to be self reactive under pressure or when shaken, or to react when combined with other agents. This is especially important if the reaction can render the chemicals in question unstable, creating the potential for fire, explosion, the release of toxic substances and other results that could have serious implications for the safety of those in the vicinity. Accidental or uncontrolled chemical reactions can cause severe personal injury and property damage, and are therefore a major concern in for those in charge of workplace safety.
Safeopedia explains Reactivity
Highly reactive chemical can undergo dramatic reactions that result in fire or explosion, but even slow reactions can be dangerous. For example, drums that become over-pressurized may not explode, but could rupture at any time and release their contents. Fires caused by reactive materials are often more dangerous than other types of fire because the heat may cause unpredictable chemical reactions.