Each laboratory should maintain an inventory of the chemicals stored in the laboratory. Each chemical should have a designated storage place and should be returned to that place after each use. The storage arrangement must be based on hazard class, not the alphabet, and should be posted to show the exact location of the chemical groups. Chemical storage areas should be inspected annually for outdated or unneeded items, illegible labels, leaking containers, etc. For advice on developing an inventory system, please contact the Health and Safety Office.

It is very important that containers of highly toxic, highly volatile, malodorous, carcinogenic or reactive chemicals be tightly sealed to prevent leakage, odors, or reaction with air. Make sure that caps and other closures are tight on all hazardous chemicals. An exception is bottles of waste, such as acid-organic mixtures that may generate gas pressure sufficient to burst a tightly sealed bottle. The best seal is the screw-cap with a conical polyethylene or Teflon insert. The caps can then be sealed with tape or Parafilm "M" as a further precaution. Additional protection can include the following (a) wrapping in an absorbent paper and sealing inside a plastic bag and (b) storing the bag inside a metal can with a friction-fitting lid.

The real, or "life-cycle", cost of a chemical includes its initial purchase price plus the ultimate disposal costs. The quantity of chemicals accumulated in the laboratory should be kept at a minimum to reduce the risk of exposures, fires, and waste disposal problems. Smaller package sizes provide the following advantages:

Frequently, it costs many times more than the original purchase price to dispose of leftover chemicals. The current cost of waste disposal runs from $1.00 per gallon for non-halogenated solvents to $50.00 per pound, including the weight of the container, for reactives, e.g., sulfides, cyanides, flammable solids. Scientific Stores and Chemistry Storeroom keep supplies of the most frequently used solvents and chemicals to lessen the need for laboratory stock piles.

Most chemical manufacturers include chemical storage information on labels. Some chemical manufacturers use color codes on labels and/or caps to indicate health, physical, and chemical hazards. These colors can be used as a guide for storage groups - store same colors together, segregated from other colors. Some manufacturers use the National Fire Protection Association (NFPA 704) hazard warning diamond symbol, the "Hazard Materials Identification System" (HMIS) colored rectangle or bar, and some labels use picture glyphs, all of which are helpful for storage information. Unfortunately the color schemes are not always consistent among manufacturers. Under most schemes, colors convey the following message:

Optimally, incompatible chemicals, such as acids and alkalis, should be stored completely separate from one another to prevent mixing in the event of an accidental spill or release of the materials. Limited storage space within the laboratories, however, prohibits such prudent practice of chemical segregation and storage. If space is limited, it is permissible to store incompatible chemicals in the same storage cabinet provided that the chemicals are segregated according to their hazard class and stored in tubs, trays, or buckets while in the cabinet. These secondary containers reduce the chance that incompatible chemicals will inadvertently come in contact with each other.

Laboratory Hoods. Chemicals should not be stored in laboratory hoods because they may impede airflow, reducing the effectiveness of the hood.

Refrigerated Storage. Flammable solvents that require storage at reduced temperature are to be stored only in refrigerators or freezers designed for the storage of flammable liquids. "Safety" refrigerators for flammable liquid storage and "explosion-proof" refrigerators are both acceptable. Ordinary household refrigerators are not to be used for the storage of flammable liquids because of interior arcing contacts. Because there is no venting of the interior spaces in refrigerators and freezers, all chemicals should have tightly sealed caps. Signs should be applied to the doors of chemical refrigerators stating: NO FOOD, BEVERAGE, OR ICE FOR HUMAN CONSUMPTION."

Cold rooms have closed air-circulation systems and recirculate any leaks and escaped vapors within the chamber. The refrigeration coils in cold rooms are aluminum and subject to damage from corrosive atmospheres. The electrical systems are designed with vapor-proof lights and duplex outlets, but frequently are compromised by extension cords and plug strips. Cold rooms are not acceptable for storage of flammables, dry ice, or liquid chemicals. If these chemicals need to be refrigerated, they are to be stored in an approved refrigerator or freezer, rather than a cold box. A warning sign should be posted on the door as illustrated:

Flammable Liquid Storage. Fire protection regulations limit the storage of flammable liquids to 10 gallons in open storage, 25 gallons in "safety cans", and 60 gallons in "flammable liquid storage cabinets" per laboratory unit. These limits are for the total quantities on hand, including chemicals in storage, chemicals in use, and wastes.

Cabinets and Shelves. Cabinets under hoods and laboratory benches can be used for storage of chemicals. However, storage near or under sinks where there may be exposure to water is to be avoided. Cabinets for chemical carcinogens or highly toxic chemicals should be locked.

Dessicator Jars or Cabinets. Dessicator jars and cabinets are useful for storage of air and water reactives, toxics, and malodorous chemicals. In case of especially malodorous compounds, i.e., mercaptans, replace the dessicator material with a vapor adsorber (e.g. charcoal) to control odors.

Bench Tops. Storage of chemicals on bench tops is undesirable. Such storage is more vulnerable to accidental breakage by laboratory, housekeeping, and emergency response personnel.

Storage by Compatibility

Chemicals should be stored in the laboratory according to their chemical compatibility. Chemicals should not be stored in alphabetical order since this practice may place incompatible chemicals next to each other (e.g., sodium cyanide and sulfuric acid) which increases the potential for accidental mixing of incompatible chemicals. The diagram, "Suggested Shelf Storage Pattern," (Appendix 4-A) indicates a recommended arrangement of chemicals according to compatibility. These compatibility groups should be stored separately, especially chemicals with an NFPA 704 or HMIS reactive rating of 3 or higher, and in dedicated labeled cabinets. Within any compatibility group, chemicals may be arranged alphabetically to facilitate ease of retrieval.

The following compatibility groupings are recommended:

Store large bottles of acid on low shelves, in special acid cabinets, or cabinets under lab benches. Place acids in plastic trays for secondary containment in case of breakage, especially glass cleaning solutions of chromic acid. Segregate inorganic and oxidizing acids from organic compounds including organic acids and other combustible materials. Segregate nitric acid (>40%) from other inorganic acids. Store acids separate from bases and other reducing agents. Inorganic salts, except those of heavy metals, may be stored in this group. Glacial acetic acid should be stored with flammable and combustible materials since it is combustible.

Segregate bases from acids and oxidizers on shelves near the floor. The preferred storage container for inorganic hydroxides is polyethylene instead of glass. Place containers in trays for secondary containment in the event of leakage or breaks.

Organic compounds should be segregated from inorganics. Organics and inorganics with NFPA 704 or HMIS reactive hazard rating of two (2) or less may be stored together. Chemicals with a reactive hazard rating of three (3) or four (4) are to be stored separately.

Fire regulations limit the quantity of flammable and combustible liquids to 10 gallons in open storage and use, 25 gallons in safety cans, and 60 gallons (30 gallons maximum per cabinet with a maximum of 2 cabinets per room) in flammable storage cabinets. The materials are to be stored away from sources of ignition such as heat, sparks or open flames and are to be segregated from oxidizers.

Store inorganic oxidizers in a cool dry place away from combustible materials such as zinc, alkaline metals, formic acid, and other reducing agents. Inorganic salts may also be stored in this group. Store ammonium nitrate separately.

Certain chemicals are shock or heat sensitive or become that way in storage. Some chemicals form explosive peroxides or react violently with other chemicals. Benzoyl peroxide is shock and heat sensitive. Ethers and other peroxidizable compounds form shock sensitive peroxides in storage. Picric acid is classified as a Class A explosive when it contains less than 10% water. Store shock and heat sensitive chemicals in a dedicated cabinet.

Water Reactives. Water reactives should be stored in cool dry place protected from any water source. A Class D fire extinguisher should be available in case of fire. As an added precaution, containers are to be stored in trays or other secondary containers filled with sand.

Pyrophoric (Air Reactives). Pyrophorics should be stored in a cool, dry place making provision for an air-tight seal. White or yellow phosphorous should be stored under water in glass-stoppered bottles inside a metal can for added protection.

The compounds react with acids to release highly toxic gases. They must be isolated from acids and other oxidizers.

A dedicated lockable storage cabinet in a "designated area" is the preferred storage method for highly toxic and carcinogenic chemicals. They should be stored in unbreakable, chemically resistant, secondary containers. The storage cabinet must be posted with a sign stating HIGHLY TOXIC OR CANCER-SUSPECT AGENT. A separate inventory of all highly acute toxics, carcinogens, and reproductive toxins should be maintained.