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7.11 Chemical Segregation

Chemicals should be stored according to compatibility and hazard classes. Rather than store chemicals alphabetically, or by carbon number, or by physical state, etc., EHS recommends that you segregate them by DOT hazard class first.   The potential hazards of storing incompatible chemicals together, and when an emergency occurs, include:

  • Generation of heat. 
  • Possible fires and explosion. 
  • Generation of toxic and/or flammable gases and vapors. 
  • Formation of toxic compounds. 
  • Formation of shock and/or friction sensitive compounds. 
  • Violent polymerization.
  • The benefits of chemical segregation by hazard class include:
  • Safer chemical storage. 
  • Understanding the hazards a chemical exhibits will increase your knowledge about the chemical. 
  • Identifying potentially explosive chemicals. 
  • Identifying multiple containers of the same chemical.

There are a number of segregation schemes recommended in the literature by government agencies, chemical manufacturers, safety supply companies, and other universities. However, EHS is recommending segregation of chemicals using a modified version of the Department of Transportation (DOT) Hazard Class System. While this modified DOT system results in most common chemicals being segregated properly, there is no one system that solves all problems. The modified DOT system is less complicated than other segregation schemes and the information to make decisions of which hazard classes to use can easily be found in SDSs, container labels, container markings and stickers, and other resources.

Please note: that DOT hazard classes segregate chemicals according to the hazards posed during transportation and not necessarily based on health hazards. Keep in mind that chemicals do not always fall neatly into one hazard class and can pose multiple hazards – including both physical and health hazards (such as flammable liquid, corrosive or flammable liquid, poison).

When you are making decisions on how to segregate, keep in mind the following:

  • Physical hazards of the chemical.
  • Health hazards of the chemical. 
  • The chemical form (solid, liquid or gas).
  • Concentration of the chemical.

Segregation of different chemical hazard classes (such as acids and bases) can occur in the same cabinet as long as there is some form of physical separation, such as using trays with high sides or deep trays. However never store oxidizers and flammables in the same cabinet. Also, do not store compounds such as inorganic cyanides and acids in the same cabinet.

Once chemicals have been segregated, ensure everyone in the lab knows the process and what system is being used. It is best to clearly identify where chemicals in each hazard class will be stored by labeling cabinets with signs, or hazard class labels. These can be purchased from a safety supply company, you can create your own, or download FREE labels from the EHS Signs and Labels webpage..

If you need assistance with cleaning out your lab of old and excess chemicals, or would like assistance with segregating your chemicals, contact EHS at EHS also offers an online training class on Chemical Segregation. Examples of incompatible chemicals can be found in the appendix.