Storage Practices

Look around you in the laboratory. Take note of the system used to store the chemicals and the conditions and environment they are stored in. More than likely, you will see at least one of the following examples of poor chemical storage practices there in your laboratory :

chemicals stored in random order
chemicals stored in alphabetical order
chemicals stored by poorly chosen categories, such as all acids (inorganic and organic, strong oxidizers) together; all organics stored together
chemicals stored in hood while hood is in use for designed purposes
flammables stored in domestic refrigerator
food stored beside chemicals in refrigerator
chemicals stored on shelves above eye level
one bottle is sitting on the top of a second bottle
overcrowded shelves requiring manipulation of several containers to remove the container of interest
chemicals are left on benchtop where last used or shoved into out-of-the-way location to make room for ongoing experiments

shelving on which chemicals are stored is not strong enough to support chemicals or is of inappropriate material
shelves are not securely fastened to a permanent structure, such as wall or benchtop
shelves are not fitted with raised lip or tilted slightly backward
inventory control is poor or non-existent; containers are not dated; containers are obviously ancient
some containers have no labels or inappropriate labels which do not adequately describe the contents or hazards
containers are stored on the floor
caps on containers are missing or badly deteriorated

Accidents resulting from poor storage techniques are preventable. In most cases, the above poor storage practices have not yet led to disaster. However, the potential for such a disaster is extremely high. This section will provide information on alternative storage systems which are meant to circumvent outdated storage methods and lower the potential for an incompatible reaction. Before discussing categorical storage arrangements, the three alternative storage methods (random, alphabetical and incomplete categorical) will be discussed.

Random storage - By far the worst storage system involves no system at all, that is, random storage. With this system, there are no restrictions to where chemicals are stored and no limit to the number of adverse reactions that may arise due to incompatible contacts. You may find acids next to bases, oxidizers next to flammables, water reactives next to the sink and severe poisons next to the writing desk. This is a laboratory waiting for a disaster to happen.

Alphabetical storage- Probably the most common chemical storage practice in the recent past is that of storing chemicals in alphabetical order. When chemicals are stored alphabetically, the situation is improved over the random storage system, but there is still a great potential of incompatible substances coming in physical contact, particularly during an emergency situation such as a fire, spill or natural disaster. A wide variety of examples are possible to illustrate the problems associated with alphabetical storage (see Brethericks' Handbook of Reactive Chemical Hazards, or NFPA 491M : Manual of Hazardous Chemical Reactions) that may be encountered, and the danger associated with the chance encounter. The following list provides numerous of these examples.

Problems with Alphabetical Chemical Storage

Acetic acid + acetaldehyde
small amounts of acetic acid will cause the acetaldehyde to polymerize, releasing large amounts heat
Acetic anhydride + acetaldehyde
condensation reactions can be violent -- explosive
Acrolein + ammonia, aqueous
extremely violent polymerization reaction of acrolein and any alkali or amine
Aluminum metal + ammonium nitrate
potential explosion
Aluminum metal + antimony trichloride
aluminum metal burns in the presence of antimony trichloride vapor
Aluminum metal + any bromate (or chlorate or iodate)
finely divided aluminum plus these compounds produces potential explosion that is detonated by heat, percussion, friction or light.
Aluminum chloride - self-reacting
upon prolonged storage, explosion occurs when container is opened
Ammonium nitrate + acetic acid
mixture will ignite especially if acid is concentrated
Cupric sulfide + cadmium chlorate
explode on contact
Hydrogen peroxide + ferrous sulfide
vigorous reaction, highly exothermic

Lead perchlorate + methanol
explosive mixture if agitated
Maleic anhydride + magnesium hydroxide
potentially explosive reaction
Mercury nitrate + methanol
mixture has potential of forming mercury fulminate, an explosive
Nitric acid + nitrobenzene
mixtures of nitric acid and nitrobenzene may be detonated
Potassium cyanide + potassium nitrite
potentially explosive mixture if heated
Silver + tartaric acid
explosive mixture
Silver oxide + sulfur
potentially explosive mixture
Sodium + selenium
reaction attended by burning

Incomplete or Poorly chosen categorical storage

This system provides some differentiation between hazard classes of chemicals, and as such is an improvement over the alphabetical storage policy. Examples of how chemicals may be divided are listed below.

acids are stored separately, but nitric and perchloric acid are not isolated and perhaps the perchloric acid is stored on wooden (combustible) shelves
solids are stored separately from liquids, but flammable solids are stored next to solid oxidizers
organics are separated from inorganics, but flammables and extreme toxics are not segregated from the less hazardous materials
no provision is made for water reactives, either liquids or solids

Any of these categorical attempts at segregating hazard classes is better than no separation at all, and the resulting potential for dangerous contact between incompatible substances has been greatly decreased.

However, undesirable contacts are still possible and more complete classification needs to be done. This is accomplished through a complete categorical storage system.