The safest method for grouping chemicals in storage revolves entirely around preventing unintended, catastrophic reactions. Chemical incidents, such as fires, explosions, or the release of toxic gases, most often occur when incompatible materials accidentally mix. The fundamental goal of any safe storage strategy is to keep chemicals that react dangerously with each other physically separated. Achieving this separation requires moving beyond simple alphabetical storage and instead grouping substances based on their intrinsic chemical hazards and reactivities.
The Basis of Safe Grouping: Chemical Hazard Classes
The most reliable system for safe chemical storage is based on standardized hazard classification, not on the name or the manufacturer. This approach uses the intrinsic properties of the chemical to determine its appropriate storage environment and separation from others. The international standard for classifying these hazards is the Globally Harmonized System of Classification and Labeling of Chemicals (GHS), which the U.S. Occupational Safety and Health Administration (OSHA) incorporated into its Hazard Communication Standard (29 CFR 1910.1200).
The GHS categorizes chemicals into broad classes like flammables, oxidizers, corrosives, and toxics. This classification is readily available on the Safety Data Sheet (SDS) for every chemical, which is a document required by OSHA for all hazardous substances. The SDS details the chemical’s physical and health hazards and, crucially, lists incompatible materials that must be kept away from it.
Chemicals are grouped together only if they share a hazard class and are compatible with one another. For example, all flammable liquids are stored together, but they are stored separately from all corrosive acids. This method of grouping by hazard class and then ensuring compatibility within that group is the industry standard for minimizing risk.
The primary hazard classes that dictate storage grouping include flammable liquids and solids, oxidizers, corrosive acids, corrosive bases (alkalis), water-reactive materials, and highly toxic substances. Some chemicals, like glacial acetic acid, belong to multiple classes (it is both corrosive and flammable). Such chemicals must be stored with the group representing their most dangerous hazard, or in a way that respects all their incompatibilities.
Implementing Segregation: Specific Incompatibility Groups
Segregation is the practical application of hazard classification, requiring physical barriers or distance between incompatible chemical groups. The severity of the potential reaction dictates the necessary level of separation, ranging from a simple partition to entirely different storage rooms. The most common and dangerous incompatibilities involve corrosives, flammables, and oxidizers.
Acids and bases must be stored separately because their reaction is exothermic, meaning it releases a great deal of heat, which can cause violent boiling, container failure, and splashing. Strong acids, such as concentrated sulfuric acid, and strong bases, like sodium hydroxide, will react violently when mixed. Even within the corrosive group, strong oxidizing acids, such as nitric acid, must be segregated from organic acids and other combustible materials because they can accelerate a fire.
Oxidizers, which are chemicals that supply oxygen to a fire, must be kept away from all flammable and combustible materials, including organic substances like solvents. Examples of oxidizers include nitrates and peroxides, and their contact with an organic material can lead to an explosion or fire. Water-reactive materials, such as alkali metals like sodium and potassium, require complete isolation from any source of moisture, including sinks, drains, and even sprinkler systems.
Separation is achieved through either segregation (storing in different cabinets or on different shelves in the same room) or isolation (requiring storage in a dedicated, separate area or building). For highly reactive pairings, such as oxidizers and flammables, a separation distance of at least 20 feet or a physical, fire-rated barrier is often recommended. Even within a storage cabinet, corrosive acids and bases should be kept in separate spill trays to prevent a reaction if one container leaks.
Securing the Storage Area: Physical Requirements
The integrity of the storage environment is the final layer of safety, ensuring that even if a container fails, the chemical cannot escape or mix with incompatible neighbors. This involves specialized storage furniture and robust environmental controls. All hazardous liquid chemicals require secondary containment, which is a structure designed to catch and hold the contents of the primary container in case of a leak or spill.
Secondary containment systems, such as spill trays, sumps, or berms, must be constructed of a material compatible with the chemical they are designed to contain. Regulations often require that this containment capacity be at least 10% of the total volume of the stored containers or 100% of the largest container, whichever volume is greater. This measure is especially important for corrosives, where a breached container could quickly degrade shelving or concrete floors.
Specialized storage furniture is necessary to manage specific hazards, such as using fire-rated safety cabinets for flammable liquids. These cabinets are designed to contain a fire for a minimum amount of time, preventing its spread and protecting the contents from external heat sources. Corrosive chemicals must be stored in specialized cabinets made of corrosion-resistant materials, such as polyethylene or coated metal, to prevent degradation of the cabinet structure.
Storage areas also require adequate ventilation and temperature control to prevent chemical degradation or the buildup of hazardous vapors. Flammable storage should be kept cool to prevent the release of ignitable vapors, while corrosive storage often requires dedicated forced ventilation to remove corrosive fumes that could damage the building’s infrastructure or harm personnel.