​Defini​tion and Hazards

The category "Reactive" is a term given to a chemical class that displays a broad range of reactions. This category includes explosives, oxidizers, reducers, water sensitive, acid sensitive, air sensitive and unstable chemicals. These substances are capable of producing toxic gases, explosive mixtures, being explosive, reacting with water violently, or they may contain cyanide or sulfide. Reactive chemicals exhibit moderate to extremely rapid reaction rates and include materials capable of rapid release of energy by themselves (self-reaction or polymerization), and/or rates of reaction that may be increased by heat or pressure or by contact with incompatible substances.

Reactives may be broadly classified into two groups: those that may explode and those that do not. Reactivity of individual chemicals in specific chemical classes (e.g., alkali metals) varies considerably. This rate of activity may also vary as a result of aging or contamination. Reactives may be further subdivided and placed into eight classes based upon their chemical behavior.

Cl​ass I

Chemicals normally unstable that readily undergo violent change without detonating.

Properties -

1. Pyrophorics--spontaneous ignition in contact with air. Examples: metal alkyls, phosphorus, finely divided metal powders such as magnesium, aluminum, and zinc. Prevent contact with air or water - use and store in inert environments.
2. Polymerizables--spontaneous polymerization in contact with air. Examples: divinyl benzene. Keep cool and avoid contact with water.
3. Oxidizers--violent reaction in contact with organic materials or strong reducing agents. Examples: perchloric, chromic and fuming nitric acid. Use minimum amounts for procedure; do not keep excessive amounts of material in the vicinity of process; store properly, away from organic materials, flammable materials and reducers.

Class II

Chemicals that react violently with water.

Properties –

Causes large evolution of heat in contact with water, decomposes in moist air, and violently decomposes with liquid water. Examples: Sulfuric acid, chlorosulfonic acid, oleum, phosphorous trioxide and pentoxide, acetyl halides, phosphorus halides, titanium tetrachloride, glyoxal.

Precautions

1. Handle materials like corrosives. Use protective acid resistant rubber or plastic clothing with gloves and face shield.
2. Keep away from moisture.
3. Handle materials in fume hood since fuming in moist air can result in exposure to corrosive and/or toxic gases

Class III

Chemicals that form potentially explosive mixtures with water.

Properties –

Chemicals decompose violently in water with evolution of heat and flammable gases, which may ignite if exposed to ignition source. Evolution of heat with water may be sufficient to cause auto-ignition (and explosion). Examples: alkaline metals, alkaline earth metals, alkaline metal hydrides, alkaline metal nitrides.

Precautions

1. Provide ventilation to disperse flammable gases.
2. Use dry sand to smother materials - use of water as a fire extinguisher may aggravate fire.
3. Avoid contact with and handle away from water sources.

Class IV

Chemicals that, when mixed with water, generate toxic gases, vapors or fumes in quantity sufficient to present a danger to human health or the environment.

Properties –

Reacts rapidly with water with the production of gases or vapors, which are acutely toxic to human health. Examples: alkaline metal phosphides, phosphorus halides, aluminum phosphide, toluene diisocyanate.

Precautions

1. Provide adequate ventilation when handling.
2. Keep containers sealed.
3. Do not handle near water.

Class V

Cyanide or sulfide bearing chemicals.

Properties –

Acid sensitive cyanides and sulfides that produce extremely toxic hydrogen cyanide or hydrogen sulfide gases on contact with acids or materials which form acids in the presence of moisture or liquid water.

Examples: metal cyanide salts, organic cyanide compounds, metal sulfide salts, organic sulfides and mercaptans.

Precautions

1. Do not store in cabinets with acids and oxidizers.
2. Isolate from other reactive chemicals.
3. Protect sulfide salts from moisture.
4. Provide adequate ventilation due to severe inhalation hazard of hydrogen cyanide and hydrogen sulfide and acute toxic effects from skin contact with hydrogen cyanide.

Class VI

Chemicals capable of detonating or exploding if subjected to a strong initiating source or if heated under confinement.

Properties –

Detonation or explosion can occur if heated above ambient temperature; or if exposed to an initiating source such as shock, mechanical shock, spark or flame, or a catalyst that accelerates decomposition. Examples: lead amide, sodium amide, thallous nitride, metal azides, brominated organic compounds, benzene diazonium salts, ammonium picrate, ammonium tetra-chromate, metal periodates, organic perchlorates, isoamyl nitrite, ammonium nitrate & chlorate.

Precautions

1. Protect containers from physical damage, heat and incompatible chemicals.
2. Chemicals in this class exhibit a wide range of other properties, i.e., flammability, acid or water or light sensitivity. Know the properties of the materials being worked with.
3. Check SDS for information on incompatibles when storing.

Class VII

Chemicals readily capable of detonation, explosive decomposition, or reaction at standard temperature and pressure.

Properties –

Chemicals capable of detonation or explosive decomposition under ambient temperature and pressure without any external initiating source. Examples: ammonium chlorate, organic azides, metal azides, benzoyl peroxide, peroxidized ethers.

Precautions

1. Materials should only be handled by knowledgeable and trained individuals.
2. Evaluate chemicals periodically to determine whether deterioration has occurred. If so, dispose of properly by contacting Environmental Health & Safety.
3. Check the SDS for information on incompatibles for storage and chemical properties of materials handled.
4. Follow recommendations on SDS for personal protective equipment.

Class VIII

Forbidden explosives, Class A explosives, and Class B explosives as defined in 49 CFR 173.

Properties –

Forbidden Explosives are capable of detonation or explosive decomposition under ambient conditions, considered too dangerous for transportation. Examples: Forbidden explosives: diethylene glycol dinitrate, unstabilized nitroglycerine, nitrocellulose. Class A Explosives: TNT, mercury fulminate, diazo-dinitrophenol, lead 2,4-dinitroresorcinate. Class B. Explosives: stabilized nitrocellulose, stabilized nitroglycerin.

Precautions

Materials should only be handled by experienced and properly equipped persons.

Resource

Pyrophoric Reagents Handling in Research Labs