The Basics
Chemical segregation is important to prevent fires, explosions, toxic or flammable gas release, and other damaging or adverse reactions in chemical storage.
The first rule of chemical segregation is to sort chemicals by their reactivity and incompatibility. It's OK to separate out chemicals by owner or to alphabetize, but only if you can still segregate incompatible chemicals. For example, you might set aside two shelves of a flammable liquid storage cabinet for one user's flammable chemicals, and then sort those two shelves with spill trays to separate the various incompatible groups.
There are some types of chemicals that should be stored in completely separate locations from each other, such as in separate cabinets. Follow these rules first, then proceed to segregation within storage locations.
Keep Mineral Acids away from Organic Solvents: Mineral acids, especially the oxidizing acids such as nitric and perchloric acid, must never be stored in the same cabinet as volatile/flammable organic materials. Accidental mixing of nitric acid with common solvents has caused multiple laboratory explosions and fires.
Keep Oxidizers away from Organic Solvents: Oxidizers (nitrate and nitrite salts, hydrogen peroxide, etc.) must never be stored with volatile/flammable organic liquids. Uncontrolled mixing of these two groups is also a cause of fires in laboratories.
Keep Ammonia away from Oxidizing Acids: Ammonia (also known as ammonium hydroxide) must never be stored in the same cabinet with oxidizing acids such as nitric acid or perchloric acid. The gases that are released from the solutions will react in the air to form shock-sensitive explosive compounds like ammonium nitrate and ammonium perchlorate, which appear as crystal growth on bottles, caps and the walls of the cabinet.
Keep Bleach away from Acids: Bleach should never be stored with acids of any kind, particularly with hydrochloric acid. The mixture of bleach with acids produces hypochlorous acid, which then decomposes in low pH to chlorine gas, which is immediately dangerous to life and health at only 30ppm. The mixture of hydrochloric acid and bleach is particularly prone to chlorine gas production.
Keep Bleach away from Ammonia: Bleach should never be stored with ammonia (ammonium hydroxide) solutions. The mixture of bleach with ammonia produces toxic and corrosive chloramine gases.
Note: Bleach is one of the few items that may be stored in a cabinet under a sink, which is convenient for complete segregation of bleach from incompatible materials.
Keep Cyanide Salts away from Acids: The mixture of acids (whether organic or mineral) with cyanide salts (NaCN, KCN, etc.) will produce hydrogen cyanide gas, which is immediately dangerous to life and health at 50ppm.
Keep Sulfide/Selenide Salts away from Acids: Acids react with sulfide and selenide salts (Na2Se, Na2S, etc.) to produce hydrogen sulfide or hydrogen selenide gas, which are acutely toxic even in the part per million concentration range.
Keep Pyrophorics away from Flammable/Combustible Liquids: If a pyrophoric material catches fire in storage and is already inside the flammable storage cabinet with other flammable materials, then the flammable storage cabinet will not protect the flammable materials inside from the fire. Pyrophoric materials should be stored in a separate flammable cabinet from other flammable materials in order to minimize the damage if one ignites in storage. For better protection, store pyrophoric materials in an inert atmosphere glove box.
Other types of chemicals simply need to be separated by containment tray or bin, or on separate shelves in a cabinet, to prevent accidental mixing in case the bottles break. This site provides specific guidance for how to segregate the chemicals in a storage location from each other, using secondary containment trays or bins.
