Storage Practices

• 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 This section will provide information on alternative storage systems which are meant to circumvent outdated storage methods and lower the potential for an incompatible reaction.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
• Sodium + silver bromide, silver chloride, silver fluoride, or silver iodide
  forms impact-sensitive systems
• Sodium + sulfur
  reaction proceeds with explosive violence
• Sodium + stannic halides
  forms impact-sensitive mixtures
• Sodium cyanide + sulfuric acid
  release of HCN gas, death

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.