The chemical incompatibilities shown below are not exhaustive.  As a result, it is important for Laboratory personnel to research the properties of the chemicals they are using. Use sources such as SDSs for guidance on chemical incompatibility.  Also ensure you read the container's label – it should also have storage guidelines.

X = Not compatible—do not store together

Storage requirements are provided below.  Consult the chemical’s Safety Data Sheet for specific storage and incompatibility.

• Store acids and bases separately from each other and from other incompatible chemicals.  For example, store oxidizing acids (such as nitric, perchloric, and sulfuric acids) separately from combustible and flammable liquids/materials.
• Segregate acids from reactive metals such as sodium, potassium, and magnesium.
• Nitric acid and hydrochloric acid may be stored in the same corrosive storage cabinet, but they must be kept in separate drip trays.  These can combine to form chlorine and nitrosyl chloride gases—both are toxic. 
• Segregate organic acids (acetic, formic, etc.) from mineral acids (nitric, hydrochloric, etc)  by use of separate secondary containers.  These acids are combustible and will react if they  come in contact with an oxidizing acid.
• Segregate acids from chemicals that could generate toxic or flammable gases upon contact, such as sodium cyanide, iron sulfide and calcium carbide.
• Store in a cool, dry environment free from extremes of temperature and humidity.
• Store in sealed, air-impermeable containers. Containers with tight-fitting caps are necessary. Containers with loose-fitting lids or glass stoppers should not be used.
• Do not store piranha etch (a mixture of 98% sulfuric acid and 30% hydrogen peroxide in ratios ranging from 2-4:1) , aqua regia (1:3 mixture of concentrated nitric and hydrochloric acids), or Nitol (a mixture of nitric acid and ethanol that becomes explosive if the nitric acid exceeds 10%).  Make these solutions just prior to use and dispose of left over material with the process waste in a “vent-able” container. (See Waste)
• Use storage cabinets specifically designed for corrosives. These should be connected to exhaust ventilation whenever possible. Usually, at least one of the cabinets directly under the fume hood will be passively connected to the fume hood exhaust.
• Use secondary containment for all liquids. Do not store aqueous sodium and potassium hydroxide solutions in aluminum drip trays.  These will corrode aluminum and compromise its integrity.

Storage requirements are provided below: Consult the chemical’s SDS for specific storage and incompatibility.

• Segregate bases from acids, metals, explosives, organic peroxides and easily ignitable materials.
• Do not store aqueous sodium and potassium hydroxide solutions in aluminum drip trays.  These will corrode aluminum.
• Store in a cool, dry environment free from extremes of temperature and humidity.
• Store in sealed, air-impermeable containers. Containers with tight-fitting caps are necessary. Containers with loose-fitting lids or glass stoppers should not be used.
• Use storage cabinets specifically designed for corrosives. These should be connected to exhaust ventilation whenever possible. Usually, at least one of the cabinets directly under the fume hood will be passively connected to the fume hood exhaust.
• Use secondary containment for all liquids. Do not store aqueous sodium and potassium hydroxide solutions in aluminum drip trays.  These will corrode aluminum and compromise its integrity.

Flammable and combustible chemicals include liquids such as organic solvents, oils, greases, tars, oil base paints, and lacquers, as well as flammable gases. Flammable gases are discussed in the Georgia Tech Dangerous Gas Safety Program.

The emphasis of this section is on flammable and combustible liquids.

Flammable and combustible liquids are defined by their flash points. The flash point of a liquid is the minimum temperature at which it gives off sufficient vapor to form an ignitable mixture with the air near its surface or within its containment vessel.  A liquid’s flash point is a function of its vapor pressure and boiling point.  Generally, the higher the vapor pressure and the lower the boiling point of a liquid, the lower its flash point will be.  The lower the flash point, the greater the fire and explosion hazard

Flammable and combustible liquids are classified by the National Fire Protection Association (NFPA) based on their flash points:

Flammable Liquids (Class I):

Liquids with flash points below 100°F (37.8°C) and vapor pressures not exceeding 40 pounds per square inch (absolute) at 100°F (37.8°C).  Flammable Class I liquids are subdivided as follows:

• Class IA: Liquids having flash points below 73°F (22.8°C) and boiling points below 100°F (37.8°C). Flammable aerosols (spray cans) are included in Class IA. (These are  4 on an NFPA Diamond)
• Class IB:  Liquids having flash points below 73°F (22.8°C) and having boiling points at or above 100°F (37.8°C). (These are a 3 on an NFPA Diamond)
• Class IC:  Liquids having flash points at or above 73°F (22.8°C) and below 100°F (37.8°C).  The boiling point is not considered. (Also a 3 on an NFPA Diamond)

Combustible Liquids (Classes II and III):

Liquids having flash points at or above 100°F (37.8°C).  Combustible liquids in Classes II and III are subdivided as follows:

• Class II:  Liquids having flash points at or above 100°F (37.8°C) and below 140°F (60.0°C).
• Class IIIA:  Liquids having flash points at or above 140°F (60.0°C) and below 200°F (93.4°C).

Storage requirements are provided below. Consult the chemical’s Safety Data Sheet for specific storage and incompatibility.

Oxidizers are compounds that supply their own oxygen and heat (ignition source) when in contact with organic compounds. These are chemicals that can react vigorously and explode.

Common oxidizing liquids and solids include:

• bromine
• bromates
• chlorinated isocyanurates
• chlorates
• chromates
• dichromates
• hydroperoxides
• hypochlorites
• inorganic peroxides
• ketone peroxides
• nitrates
• nitric acid
• nitrites
• perborates
• perchlorates
• perchloric acid
• periodates
• permanganates
• peroxides
• peroxyacids
• persulphates

Storage requirements are provided below. Consult the chemical’s Safety Data Sheet for specific storage and incompatibility.

• Store in noncombustible secondary containment (glass).  Do not store directly on combustible shelving.
• Keep away from combustible and flammable materials.
• Keep away from reducing agents such as zinc, alkali metals, and formic acid.

Water reactives are chemicals that react with water, sometimes violently, and may produce toxic or flammable gases. Examples of water reactive substances include sodium, potassium, and phosphorous pentachloride.

Storage requirements are provided below. Consult the chemical’s SDS for specific storage and incompatibility.

• Store in a cool, dry place, away from any water source.
• Make certain that a Class D fire extinguisher is available in case of fire.
• Separate alkali metals from incompatible chemicals. In addition to being water-reactive, alkali metals can also react with oxygen, acids, halogenated hydrocarbons, and carbon dioxide). Consult the SDS for specific storage guidelines.
• Store all metals in the container provided by the manufacturer.
• Store alkali metals under mineral oil or in an inert atmosphere. NOTE: Lithium may react with nitrogen. Containers should be stored in a cool, dry environment, away from light and free from extremes of temperature and humidity.
• Use secondary containment

Pyrophorics are chemicals that will ignite spontaneously in air at temperatures 130oF (54.4oC) or less. Titanium chloride and white phosphorous are examples of solid pyrophorics; t butyl lithium and tributylaluminum are examples of pyrophoric liquids.

Storage requirements are provided below. Consult the chemical’s SDS for specific storage and incompatibility.

• If in original (unopened) container, store in a cool, dry place, making provisions for an airtight seal.
• Store in a glove box under an inert atmosphere after the container has been opened.

Extremely toxic chemicals are chemicals that have a Lethal Dose 50 Percent (LD50) of 5 milligrams or less per kilogram (mg/kg) of test animal body weight. (Seven drops or a “taste” to a human.)  LD50  is defined as the dose at which 50% of the test animals died, usually within 1-2 hours. These chemicals are so toxic that their use and location must be accounted for at all times.  These chemicals will be segregated according to their physical properties, (acid, base, flammable) but with the additional requirement of that they must be kept in a locked cabinet (or refrigerator) inside a locked lab.  The PI or Lab Manager must be responsible for the key and there must be a sign out sheet to document who uses the material and how much.  Examples of chemicals with a LD50  < 5 mg/kg include puffer fish toxin and botulism toxin. 

Peroxide formation in common laboratory chemicals is caused by an autoxidation reaction.  The reaction can be initiated by light, heat, introduction of a contaminant, or the loss of an inhibitor.  Some chemicals have inhibitors such as BHT (2,6-di-tert-butyl-4-methyl phenol) hydroquinone and diphenylamine to slow peroxide formation. Most organic peroxide crystals are sensitive to heat, shock, or friction, and their accumulation in laboratory reagents has resulted in numerous explosions.  For this reason, it is important to identify and control chemicals that form potentially explosive peroxides. 

In general, the more volatile the compound, the greater its hazard, since the evaporation of the compound allows the peroxide to concentrate.  Peroxide accumulation is a balance between peroxide formation and degradation. Some common compounds that are known to form peroxides are listed in the following table.  NOTE: This is not an exhaustive list. Researchers must consult the SDSs and other sources of information for the chemicals used in their work areas to determine their peroxide-forming potential. Group A are chemicals that spontaneously form peroxides on exposure to air without further concentration or evaporation.  These materials should be tested or disposed of within three months of opening (testing is discussed later in this section).  Group B lists chemicals that form peroxides only upon concentration by evaporation or distillation.  The materials in this list should be tested or disposed of within one year of opening their containers.  Group C is a representative list of monomers that form peroxides that may act as a catalyst, resulting in explosive polymerization.

Notes

1. When stored as a liquid monomer.
2. Although these form peroxides, no explosions involving these monomers have been reported.
3. Also stored as a gas in gas cylinders.
4. Kelly, R.J., Review of Safety Guidelines for Peroxidizable Organic Chemicals, Chemical Health and Safety, September/October, 1996.
5. National Research Council, Prudent Practices in the Laboratory, Handling and Disposal of Chemicals; National Academy Press; Washington, D.C., 1999. 
6. Clark, D.E., Peroxides and Peroxide-Forming Compounds, Chemical Health and Safety, September/October, 2001.
7. This material is peroxidizable but not dangerous unless distilled or concentrated. Testing (see “Peroxide Testing Method”) is required only prior to distillation or concentration.

Storage requirements are provided below. Consult the chemical’s Safety Data Sheet for specific storage and incompatibility

• DO NOT TOUCH OR DISTURB A PEROXIDE FORMER THAT HAS VISIBLE CRYSTALS as the crystals are explosive and are shock, friction, and heat sensitive- call EHS at 404-894-6224 for help in removing.
• Label bottles with date received and date opened as this is essential in assessing the level of hazard that the material poses.
• Most peroxide forming chemicals are also flammable liquids:  Follow the storage guidelines in Flammable and Combustible Liquids (above) if the material is either flammable or combustible.
• Store in airtight containers in a flammable storage locker.
• Segregate from oxidizers and acids.
• Store peroxide-forming chemicals in a cool, dry environment, away from light and free from extremes of temperature and humidity.
• All peroxide-forming chemicals should be stored in sealed, air-impermeable containers.  Dark amber glass containers with tight-fitting caps are required.  Containers with loose-fitting lids or glass stoppers should not be used.
• Use secondary containment for all liquids.