Many laboratories find it convenient to store their chemicals alphabetically. This may seem like good lab organization, but it can lead to incompatible hazardous chemicals being stored together.

For example, say we store all the chemicals starting with "S" together. What usually happens in this situation is Sulfuric Acid (Strong Acid) gets stored on the same shelf or in the same cabinet as Sodium Nitrite (Strong Oxidizer). If one of these containers leaked (or the shelf falls), an acid gas could result as a reaction between the two chemicals. Consult the chemical's SDS for identifying hazards and compatibility issues.

Resources and information can be found on: Chemical Segregation Tip Sheet , Segregation of Waste Chemicals, and Chemical Substance Incompatibilities.

Tips on chemical storage:

• Separate solids from liquids. 
  • Note: Within the solids group, separate metals from non-metals. Keep metals away from water and moisture to prevent corrosion or reaction.
• Separate non-hazardous from hazardous. While not comprehensive, an easy way to start identifying hazardous chemicals is to look for any of the GHS hazard symbols, the signal words "danger" or "warning", or other hazard symbols if purchased before 2015.
• Separate toxic from irritants (non-hazardous).
  • Note: Irritants are usually denoted by a black "X" on the bottle. Toxic are labeled with a skull-and-crossbones symbol. Toxic chemicals should be stored away from the sink and sanitary areas.
• Separate flammable liquids (or solids)from all other hazardous chemicals.
  • Note: If you have more than 10 gallons of flammable liquid in your lab, they must be stored in a flammable storage cabinet. Flammable liquids also can be stored in cabinets underneath fume hoods.
• Separate reactives/oxidizers from remaining hazardous chemicals.
  • Note: Oxidizers can be stored on shelves, preferably below eye level. Some oxidizers can be stored in explosion-proof refrigerators to prevent peroxide formation. Water-reactive chemicals should be stored clear of a sink or any areas of moisture.
• Separate corrosives from remaining hazardous chemicals including flammables. This category contains most acids and bases, which should be separated from each other. Acids and bases can be stored in the same cabinet as long as they are stored in secondary containment separate from each other. Corrosives can be stored in cabinets underneath fume hoods (usually in the cabinet provided on the right). They may not be stored above eye level.
• Separate organic acids from inorganic acids. Inorganic acids (also known as mineral acids) are generally stronger than organic acids and include sulphuric, hydrochloric, boric, and hydrofluoric acid. They often are oxidizing agents while organic acids may be combustible, so they should not be stored together. 

Common findings relevant to chemical storage:

Chemicals not segregated by compatibility — acids are stored with flammables; oxidizers are stored with flammables: 

Various adverse events that may occur because of reactions between incompatible materials include fire, explosion, violent reactions, and/or release of toxic gases. Chemicals must be classified by hazard class and stored with regard to reactivity. Alphabetic order alone is insufficient, and chemicals must be stored in a single layer. Use the printed hazard icons on chemical labels to determine hazard class, or use the SDS if the icons are not present.

Flammables found in household refrigerators or household refrigerators not labeled to prohibit flammables: 

A non-explosion-proof refrigerator does not have the proper electrical wiring for storing flammable liquids and can be an ignition source for accumulated flammable vapors. If your flammable material must be chilled before use, use an ice bucket as needed or purchase an explosion-proof refrigerator. An explosion-proof apparatus is defined in the National Electric Code as follows: "Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby." An explosion refrigerator needs to be listed by Factory Mutual (FM), Underwriters Laboratory (UL), or other recognized testing laboratory and labeled as such. Flammable liquids stored in a non-explosion-proof refrigerator need to be removed.

Water-reactive chemicals are stored near water: 

Water-reactive chemicals must be stored away from faucets, sinks, and other sources of moisture. Store in a desiccator or under an inert atmosphere, if available.

Some examples of water-reactive chemicals: