Reactive Substances

Reactive Substances

Highly reactive chemicals can lead to reactions which involve the release of energy (heat) in relatively high quantities or at a rapid rate. Reaction rates almost always increase rapidly as the temperature

increases. If the heat evolved in a reaction is not dissipated, the reaction rate can increase until an explosion results.

Examples of reactive hazards:

  1. Some chemicals decompose when heated. The heat initiated decomposition of some substances, such as certain peroxides are almost instantaneous. Organic peroxides are a special class of compounds that have unusual stability problems that make them among the most hazardous substances normally handled in laboratories.
  2.  Some substances can detonate as a result of contamination. Mixtures of perchloric acid with a wide variety of materials, such as organic matter, can be highly unstable.
  3. Light and mechanical shock can also be initiators of explosive reactions. Hydrogen and chlorine react explosively in the presence of light. Acetylides, ozides, organic nitrates and many peroxides are examples of shock-sensitive materials. Organic peroxides are a class of compounds even more shock sensitive than explosives such as TNT or picric acid.
  4. Other substances may form unstable substances during chemical operations or prolonged storage (eg. certain ethers, alcohols and aldehydes can form peroxides). For this reason bottles of materials prone to peroxidation should not be kept for prolonged periods once they have been opened.
  5. Some chemicals are inherently unstable and can detonate under certain conditions of pressure and temperature (eg. acetylene).
  6. There are materials that are highly reactive when exposed to air (eg. finely divided metals: calcium, metal hydrides: potassium hydrides).
  7. Other compounds may react violently with water (eg. alkaline earth metals: potassium, sodium). These compounds should therefore be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene.
  8. Oxygen tanks : Serious explosions have resulted from contact between oil and high-pressure oxygen. Oil should not be used on connections to an oxygen cylinder.
  9. Hazardous Polymerization: Polymerization is the process of forming a polymer by combining large numbers of chemical units or monomers into long chains ( e.g. polyethylene from ethylene or polystyrene from styrene). Uncontrolled polymerization can be extremely hazardous. Some polymerization processes can release considerable heat or can be explosive.
  10. Incompatible chemicals: When storing, using or disposing of chemicals, care must be exercised to minimize the consequences of accidental mixing of incompatibles by spillage or breakage. Such contact could result in a serious explosion or the formation of substances that are highly toxic or flammable or both.

Some incompatible groups include:

  • acids and bases
  • flammables and toxics
  • flammables and oxidizers
  • oxidizers and reducers

Health Effects of Toxic Chemicals