ASHLEY AUGSPURGER, PhD, CSP, is the chemical hygiene officer and biosafety officer for Corteva Agrisciences in Johnston, Iowa.
RACHAEL PERRIELLO is a research safety professional at the University of Minnesota Duluth.

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Best Practices for Proper Chemical Storage
Most occupational and environmental health and safety professionals have frightening stories of poor chemical storage practices and their consequences. OEHS professionals have reported peroxide-forming chemicals being kept past their expiration date and exploding, old tetrahydrofuran (THF) bottles blowing up and forming crystals in refrigerators, water-reactive chemicals stored under sinks, badly corroded containers of air- or moisture-sensitive chemicals stored on open shelves, and finding picric acid, a shock-sensitive chemical, in a refrigerator. Serious accidents can be avoided by properly storing chemicals.
There are two components for safe chemical storage. First, chemical hazards must be identified, which will determine how and where they need to be stored. Second, users must determine chemicals’ compatibility with each other and therefore what chemicals can be stored together. These practices can be managed through good housekeeping and by keeping updated chemical inventories.
KEEPING A CHEMICAL INVENTORY An up-to-date chemical inventory is the first step toward correct chemical storage practices, making it easier to identify “groups” of chemicals—such as salts, polymers, acids, and bases—and begin considering where and how they should be stored. Label chemical containers so that users can easily identify their contents. For chemicals that can expire, like peroxide-formers, container labels should also include the contents’ expiration dates. Expired chemicals may explode or cause other accidents, so users are advised to frequently clean out their chemical storage areas and dispose of expired chemicals.
STORE THE RIGHT CHEMICALS TOGETHER Once users have correctly identified the contents of chemical containers, they can find out which chemicals can be stored together. Although storing chemicals all together may save space, if there is an accidental leak or spill, incompatible chemicals—for example, acids and bases or acids and oxidizing chemicals—can react and produce heat, vapors, or flammable mixtures.
Users should compile and refer to a list of compatible and incompatible chemicals. EPA has published a guide that specifies which chemicals can be stored together and the potential results of storing incompatible chemicals near each other in the same space (PDF). Users can also use the National Oceanic and Atmospheric Administration’s CAMEO database to identify the reactivity of chemical mixtures.
If incompatible chemicals must be stored together, secondary containment is necessary—the practice of using a second container to prevent an accidental reaction if a chemical’s primary container is breached. Requirements for secondary containment measures vary, but at a minimum, the secondary container should be able to hold 10 percent more of the total volume of chemical in the primary container.
STORE CHEMICALS IN SAFE AMOUNTS Maximum allowable chemical storage quantities are regulated under standards set by the National Fire Protection Association, the International Fire Code, and the International Building Code. NFPA 45, the organization’s standard on laboratory fire protections, details further requirements for flammable liquids, which depend upon the laboratory’s fire hazard level and the floor the lab is on.
The acceptable chemical storage quantities are set for each “control area”—typically, an area of the building that is considered separately from the rest for fire protection purposes. Storing chemicals in quantities greater than those set under the fire and building code standards may require approval from the local fire marshal and the development of specific management programs.
Storing chemicals in quantities greater than those set under the fire and building code standards may require approval from the local fire marshal and the development of specific management programs.
CHOOSE SAFE STORAGE LOCATIONS Maximum allowable storage quantities for chemicals may be increased in buildings with certain emergency systems in place, such as an automatic fire sprinkler system, or if the chemicals are kept in approved storage devices, such as flammable cabinets, safety cans, or ventilated enclosures. In multistory buildings, large chemical storage areas or high-hazard laboratories should be located on the ground level to allow for safe exit by lab personnel and quicker access by emergency responders.
Many laboratory chemicals must be kept cold to prevent them from deteriorating, but it may not be clear which refrigerator or freezer to select for storing a given chemical. For instance, explosion-proof refrigerators and freezers are sometimes confused with those designed for flammable storage. Explosion-proof refrigerators and freezers are only necessary in environments where explosive atmospheres may exist as a normal or upset condition, such as a pilot area for hydrogen gas production. In these areas, all electrical fixtures are required to be explosion-proof and portable electronics are prohibited. More information about storing chemicals in electrically hazardous locations can be found in the May 2020 Synergist article “Navigating Electrical Hazards.”
In contrast, flammable material storage refrigerators and freezers have no internal electrical components and have vapor-proof enclosures around the compressor unit to prevent explosions in cases of vapor buildup.  A best practice for cold laboratory storage is using flammable storage units as an engineering control. For laboratories that use solvents, installing flammable storage refrigerators or freezers instead of standard units is worth the additional cost to prevent accidents from occurring.
Depending on the sensitivity of the materials being stored, it may be necessary to install automated alarms in your cold storage units and have backup cold storage options. This is especially vital for chemicals that will denature or decompose and become dangerous at certain temperatures. Users can prevent chemicals like peroxides or THF from exploding by using proper cold storage units.
FLAMMABLE, CORROSIVE, AND PYROPHORIC CHEMICALS Fire and building codes and OSHA Standard 1910.106 all regulate flammable liquid storage. The standard limits storage for flammable liquids by container material and whether or not a dedicated flammable storage cabinet is used. The standard also lists requirements for flammable storage cabinet construction, including the thickness and material of the cabinet, specifications for seams and hinges, and most importantly, the cabinet’s ability to limit its inside temperature during a 10-minute fire test. It is important to purchase a flammable cabinet that meets or exceeds the standard’s requirements, because an ineffective flammable storage cabinet could cause a small laboratory fire to become catastrophic. Flammable cabinets should be inspected regularly to ensure that the hinges, latches, and any self-closing mechanisms are in good working order. Such inspections should be included in regular laboratory audits to familiarize researchers with the safety features of their equipment.
Venting is not recommended to maintain the integrity of flammable storage cabinets during a fire because it can allow flame and heat to enter or vapors to escape from the cabinet. Corrosives and toxic gases, however, should be placed in vented cabinets or enclosures whenever possible. Venting corrosive storage cabinets with metal components can prevent rusting and damage to cabinet hinges, doors, and structures, which occurs when corrosive vapors evaporate. When storing corrosives, use cabinets that are coated with corrosion-resistant lacquers or constructed from corrosion-resistant laminate. Researchers should never store corrosive liquids above counter height to minimize the consequences of spills when retrieving or returning containers.
Some of the most dangerous chemicals to use and store are pyrophoric chemicals: those that are prone to igniting spontaneously after coming into contact with air and often water as well. When it is necessary to use pyrophoric chemicals, researchers should create a standard operating procedure that includes usage precautions, procedures for safe storage and disposal, and a means of informing all researchers using and working in the laboratory of the hazards and precautions. Storing these chemicals will generally involve desiccation, controlled atmosphere chambers, and blanketing the chemicals with inert gases or liquids.
FURTHER INFORMATION If users follow the practices listed in this article, the chances of a refrigerator exploding or another accident occurring in their labs will decrease dramatically. For more information, there is a myriad of resources on chemical storage information available, including those provided by OSHA and the National Fire Protection Association. The handling and storage sections of chemical safety data sheets likewise offer useful guidance on safe storage practices.