Monday, June 22, 2009

Safe Chemical Storage Practices

Safety Cabinets
Acetaldehyde, acetic acid, cadmium chlorate, copper(II) sulfide, hydrogen peroxide, iron(II) sulfide, sodium cyanide, sulfuric acid...
Alphabetizing is a skill most of us have used since childhood, yet it can be deadly if applied to the storage of laboratory chemicals. Polymerization, explosion, and the generation of highly toxic material could result if neighboring compounds reacted on the "alphabetical" shelf above.
Properly storing chemicals such as acids, bases, and flammable or combustible liquids is essential for maintaining a safe laboratory environment. It is important to grasp the guiding principles of chemical storage, and to explore the options available from manufacturers before you buy safety cabinets for the storage of laboratory chemicals.
Chemical storage guidelines
Information on storage requirements for a given chemical can be found in the MSDS, the manufacturer's label, and chemical reference materials. Together they can provide answers to questions such as: Is the chemical flammable or combustible? Is the chemical corrosive? And Is the chemical light-sensitive? Once such information has been obtained, the appropriate place and method of storage can be determined.
Perhaps the single most important rule in chemical storage is to segregate incompatible chemicals, which could cause fire, explosion, or the generation of toxic gases. For example, acids must not be stored with bases, and oxidizers must not be stored with reducing agents or flammable materials. Chemicals that pose more than one type of hazard may require special storage arrangements.
Storing the least amount of each chemical as possible is also very important. Most chemical suppliers now offer "just-in-time" delivery, so that users can order only the amount of chemical needed for a current task and receive the order at the time it is needed. A good inventory control system also helps minimize the amounts of chemicals being stored by preventing unnecessary purchases.
Flammable and combustible liquids
At UST, CLS maintains a stock of commonly used chemicals and makes prompt deliveries to users, thus eliminating the need for PIs to over stock chemicals in their labs. Acids and corrosives Acids and corrosives While there are no specific regulatory requirements for the storage of nonflammable acids and alkaline corrosives, good storage practices dictate that these chemicals be stored in dedicated, corrosion-resistant cabinets. Acids must be stored separately from bases, and chemical compatibility must be maintained within each dedicated cabinet. For example, acetic acid and nitric acid can react explosively and must be isolated from one another if stored within the same safety cabinet. (Note: Organic acids, such as acetic acid, should be stored with organic solvents instead of inorganic acids.)
Cabinets for acids and corrosives are generally constructed of laminated or epoxy-painted plywood, high density polyethylene, or polypropylene. Epoxy-coated steel cabinets are also available; however, their use is not recommended with nitric or sulfuric acids. With these chemicals, the vapors that emanate from the stored containers contribute strongly to the degradation of metal cabinets. In the case of these two common materials, the former plywood or polymer cabinets should be utilized. It should also be noted that many cabinets also feature metal-free hinge assemblies.
Users should conduct periodic inspection and cleaning (with a neutralizing compound plus soap and water) of all safety cabinets. Look for signs of corrosion within the cabinet and carefully check trays, hinges, locks and metal shelf clips. It is important to remember that the performance of a cabinet will be compromised by corroded or improperly functioning parts.
Flammable and combustible liquids
Flammable liquids have flash points below 37.8¢XC (100¢XF). Those with flash points above 37.8¢XC are "combustibles". Flash point is the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with air near the surface of the liquid. According to the HK Fire Services Department regulations, each user must not have more than 120 liters (aggregate) of flammable materials stored outside of licensed Dangerous Goods Stores (for diethyl ether or diisopropyl ether, the aggregate value drops to 2.5 liters). In the case of temporary storage in the laboratory, the quantity must be minimized to meet only daily requirements and shall not at any time exceed the above stated limit. Furthermore, flammable materials are to be stored in appropriate flammable storage cabinets in the laboratory.
(Some of the information in this article was excerpted from Chemical Health and Safety, Vol. 4, No. 4, Jul/Aug 1997, p.33-36.)

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