To minimize the problems that might occur in the event of a major accident in a lab full of chemicals, reagents are grouped in five or six separate locations to reduce the chance of mixing in case of a disaster (shelf collapse or cabinet tipping over).
The groups are:
- Strong acids
- Strong bases
- Flammables and combustibles (including weak acids)
- General chemicals
Additional locations or containers might be set up for: radioisotopes, extremely toxic compounds, compounds that require desiccation or low temperature .
It is important to separate stored chemicals based on their chemical properties to avoid serious problems that can occur if certain combinations are accidentally mixed. This mixing is not from someone preparing a concoction in a beaker (which also could be disastrous), it refers to mishaps involving bottle breakage that can occur if a shelf collapses or a worker bangs one bottle into another while accessing the cabinet. Certain combinations can produce a violent reaction that could involve fire or explosion (in the Chemistry Department, around 1999, a number of chemical bottles fell to the floor and broke when the shelf clips failed on a cabinet full of chemicals. The Fire Department and the Hazardous Materials Response Team were summoned to respond to the incident).
Most documents on incompatible chemicals merely provide a list of combinations that are a problem. This is of some value, but another approach is to list groups that are compatible and which can be stored together as a unit. People should use both types of information to help them decide how to safely store their chemicals. I have included some examples of things commonly used in Biology labs.
1. Strong Acids: e.g. hydrochloric, sulfuric, nitric, perchloric, phosphoric
Must be stored separate from weak acids (acetic and formic are combustible) or flammable solvents. Mixing either of these with Strong acids will produce heat and may result in a fire or explosion.
- nitric acid - is also a strong oxidizer (see below).
- perchloric acid: is a very strong oxidizer when heated and can be dangerous; should always be held in a secondary container (e.g. a plastic tub).
- chloric acid: is also a very strong oxidizer.
Such strong oxidizers must not be stored near any compounds that can be oxidized (like acetic acid or any flammable solvents/solids).
2. Strong Bases: e.g. sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium oxide. Isolate in a cabinet away from Strong acids.
3. Weak Acids: e.g. acetic, formic, propionic, butyric. Store separate from Strong Acids and Oxidizers. Acetic acid and formic acids are combustible and might be stored in the Flammable storage cabinet if you do not have location reserved for Weak Acids.
4. Flammables/Combustibles: store large containers (>1 L) in a Flammable Storage cabinet. These cabinets are insulated and designed to keep the contents cool for a period should there be a fire in the lab (thus giving people time to escape before the solvents "get involved").
- alcohols: methanol, ethanol, isopropanol
- ethers: petroleum ether, diethyl ether
- organic "solvents": hexane, pentane, acetone, xylene, methylene chloride, diethylamine (although this is an organic base, it is also flammable), methyl ethyl ketone, ethylene glycol monomethyl ether (Cellosolve) and many more.
Workers need some flammables stored on the bench for easy access but try to keep as much as possible and any larger bottles (>1L) in the Flammable Cabinet. The Alberta Fire Code places limits on the quantities of Flammable/Combustible liquids that can be stored in a Flammable Storage cabinet or in a room (see "Flammable and Combustible Liquids").
5. Oxidizers: these compounds are the ones most commonly stored incorrectly with the general chemical inventory. Oxidizers can cause spontaneous ignition if mixed with a combustible material. Often these compounds contain oxygen atoms that can be donated to a reaction and increase the rate of combustion (analogous to someone fanning the kindling to try and get a camp fire going). Oxidizers must be separated from other chemicals and stored in a separate cabinet. It should be noted that the bomb used to blow up the federal building in Oklahoma City in 1995 consisted of ammonium nitrate (a lawn fertilizer and a strong oxidant) mixed with kerosene (which is combustible and can be oxidized). Further information on oxidizers can be found at the University of Nebraska site: http://bifrost.unl.edu/ehs/ChemicalInfo/oxidize.html
some examples of oxidizers:
- nitrates / nitrites: sodium nitrate, potassium nitrite - used in fireworks among other things
- chlorates and perchlorates: magnesium perchlorate is used as a drying agent.
- dichromates: sodium or potassium dichromate, might be used in acid cleaning solution.
- hydrogen peroxide: 30% (or 70%) solution - don't store in Flammable cabinet with solvents; refrigerate at 4C.
- nitric acid: store with strong acids
- perchloric acid: store with strong acids and within a secondary container (beaker or tub).
- iodine, bromine, fluorine: don't contain oxygen but are strong oxidizers.
6. General Chemicals: most of the rest of chemicals you have in the lab. There may be a few special treatments for things like very toxic substances (arsenic, cyanide) or carcinogens which might be placed in plastic bags or plastic containers to help contain the material if the bottle is dropped and to indicate to users that these require a bit more care in handling.
Thus you may need up to 5 or 6 discrete cabinets/storage areas to house these different groups. Make sure everyone in the lab understands why these separations are made. Provide clear lables on the cabinets. The Office of Environment, Health and Safety at the University of Alberta usually recommends that people not store chemicals below sinks or in other cabinets with utilities that may need repair. However, most labs do not have the luxury of not using spaces like this and I think it is acceptable to use them as long as you understand you will be responsible for clearing it out should workers need to make repairs in that area. It might be good to store items in a plastic bin or dishpan so they can be removed quickly and easily.
Depending on your workspace, you may have one or several discrete storage groups. To avoid mixing things up after they have been organized, put a sign with LARGE letters on the cabinet identifying the group and list a few members as well as a few things that should not be added. Here are a few examples that you may need to alter for your situation.
Here are the labels (DOC, 38kb) as a word document.
hydrochloric, sulfuric, nitric acid
NOT for weak acids (acetic, formic, propionic) or Flammables
ammonium hydroxide, potassium hydroxide, sodium hydroxide
NOT for Acids or Flammables
(including weak acids: acetic, formic)
NO Strong Acids
nitrates, nitrites, dichromates, iodine, persulfates