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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 This section will provide information on alternative storage systems which are meant to circumvent outdated storage methods and lower the potential for an incompatible reaction.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
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.
CATEGORICAL STORAGE
Many acceptable categorical storage schemes have been proposed and used by laboratories in academic, industrial, government and medical institutions. The common features uniting all these plans is the separation of incompatible materials. The differences in these various storage schemes arises in the number of groups that should be established for segregation purposes. The ten most commonly cited groups are flammables, oxidants, reducers, concentrated acids, concentrated bases, water reactives, extreme toxics, peroxide formers, pyrophorics and gas cylinders. The first five groups are separated to avoid accidental contact with an incompatible material which could result in a violent or explosive reaction. Water reactives are isolated to lessen the probability of their involvement in a fire situation. Extreme toxics and regulated materials (carcinogens) are segregated to provide some degree of control over their distribution and to lessen the possibility of accidental spills. Peroxide formers should be stored in a cool, dark environment, whereas pyrophorics need only contact with air to burst into flames. Gas cylinders have the added hazard, regardless of their contents, of possessing high kinetic energy due to the compressed nature of the gas.
Segregation Based on Incompatibility
There is no clear consensus on what and how many classes of chemicals should be segregated. To a large extent, how the chemical groups are divided and assigned will depend largely upon the amount of space available. More elaborate classification schemes are used by some institutions with specialized needs, the U. S. Coast Guard for instance, which breaks chemical storage into 43 separate classes.
The risk associated with incompatible chemicals coming into contact must be avoided wherever chemicals are handled or stored. In general, when chemicals react to form compounds, energy is consumed or released. When incompatible chemicals react, the generation of energy may be extremely violent resulting in catastrophic explosions. Gaseous products may be formed which are dangerously flammable, giving off vapors which can travel along benchtops to an ignition source, thus creating a dangerous fire situation. Reaction products may also release toxic vapors capable of overcoming nearby laboratory personnel. Finally, even non-hazardous vapors may be harmful if given off in a great enough volume to displace the oxygen in an enclosed area thus creating an oxygen deficient environment.
The mixing of incompatible chemicals can occur either through the accidental mixing of two reactants or when two chemicals are purposefully mixed together, such as during an experiment. In either case, disaster can be avoided if care is exercised before chemicals are handled or stored. As discussed in the previous sections, isolation of chemicals into hazard classes will eliminate most accidental adverse reactions that may occur due to breakage in the storage areas. Careful analysis of chemical properties will curtail adverse reactions involving intentional mixing of chemicals.
Chemical compatibility charts are available which outline general classes of incompatible chemicals. An example, taken from the Coast Guard's CHRIS Hazardous Chemical Data is given below which shows chemicals broken into a more elaborate storage scheme based on 24 segregated groups. Also included are examples of each reactivity group. Other excellent sources of information on chemical incompatibility include The National Fire Protection Association's publication 491M - Hazardous Chemical Reactions, and the National Research Council's Prudent Practices for Handling Hazardous Chemicals in Laboratories.
Group 1 : Inorganic Acids
Chlorosulfonic acid Hydrochloric acid
Hydrofluoric acid Hydrogen chloride
Hydrogen fluoride Nitric acid
Sulfuric acid Phosphoric acid
Group 2 : Organic acids
Acetic acid Butyric acid
Formic acid Propionic acid
Group 3 : Caustics (basic)
Sodium hydroxide Ammonium hydroxide solution
Group 4 : Amines and Alkanolamines
Aminoethylethanolamine Aniline
Diethanolamine Diethylamine
Dimethylamine Ethylenediamine
2-Methyl-5-ethylpyridine Monoethanolamine
Pyridine Triethanolamine
Triethylamine Triethylenetetramine
Group 5 : Halogenated Compounds
Allyl chloride Carbon tetrachloride
Chlorobenzene Chloroform
Methylene chloride Monochlorodifluoromethane
1,2,4-Trichlorobenzene 1,1,1-Trichloroethane
Trichloroethylene Trichlorofluoromethane
Group 6 : Alcohols, Glycols and Glycol Ether
1,4-Butanediol Butanol (iso, n, sec, tert)
Diacetone alcohol Diethylene glycol
Ethyl alcohol Ethyl butanol
Ethylene glycol Furfuryl alcohol
Isoamyl alcohol Isooctyl alcohol
Methyl alcohol Methylamyl alcohol
Nonanol Octanol
Propyl alcohol (n-, isoGroup-) Propylene glycol
Group 7 : Aldehydes
Acetaldehyde Acrolein
Butyraldehyde Crotonaldehyde
Formaldehyde Furfural
Paraformaldehyde Propionaldehyde
Group 8 : Ketones
Acetone Acetophenone
Diisobutyl ketone Isophorone
Mesityl oxide Methyl ethyl ketone
Group 9 : Saturated Hydrocarbons
Butane Cyclohexane
Ethane Heptane
Hexane Isobutane
Methane Nonane
Paraffins Paraffin wax
Pentane Petroleum ether
Group 10 : Aromatic Hydrocarbons
Benzene Cumene
Dodecyl benzene Ethyl benzene
Naphtha Naphthalene
Toluene Xylene
Group 11 : Olefins
Butylene 1-Decene
1-Dodecene Ethylene
1-Heptene 1-Hexene
1-Tridecene Turpentine
Group 12 : Petroleum Oils
Asphalt Gasolines
Jet fuels Kerosene
Oils Mineral Oil
Group 13 : Esters
Amyl acetate Butyl acetates
Castor oil Cottonseed oil
Dimethyl sulfate Dioctyl adipate
Ethyl acetate Methyl acetate
Group 14 : Monomers and Polymerizable Esters
Acrylic acid Acrylonitrile
Butadiene Butyl acrylate
Ethyl acrylate Isodecyl acrylate
Isoprene Methyl acrylate
Group 15 : Phenols
Carbolic acid Cresote
Cresols Phenol
Group 16 : Alkylene Oxides
Ethylene oxide Propylene oxide
Group 17 : Cyanohydrins
Acetone cyanohydrin Ethylene cyanohydrin
Group 18 : Nitriles
Acetonitrile Adiponitrile
Group 19 : Ammonia/ Ammonium Hydroxide
Group 20 : Halogens
Group 21 : Ethers (including THF)
Group 22 : Phosphorus, Elemental
Group 23 : Sulfur, Molten
Group 24 : Acid Anhydride
Acetic anhydride Propionic anhydride
Segregation Based on Hazard Classes
Clearly, the above level of material segregation is complex and time consuming for chemical storage in most research laboratories. What should be required as a minimum, however, is to establish and separate chemicals according to similar hazards, such as flammability, corrosivity, sensitivity to water or air, and toxicity. The following major categories of chemicals, each of which will be discussed in greater detail, are strongly recommended:
Flammables
Oxidizers
Corrosives
- acids
- bases
Highly Reactives
Extreme Toxics/Regulated Materials
Low Hazard
One problem with the implementation of this type of system of assigning chemicals to a specific storage area based on chemical hazards, is the actual identification of the hazards themselves. Recent legislation has made this task somewhat easier since all chemical manufacturers are now required to list all hazards on outgoing chemical containers and each chemical must be accompanied by a Material Safety Data Sheet (MSDS). The chemical label thus furnishes a quick method of determining whether the material is a fire hazard, health hazard or reactivity hazard. The MSDS furnishes more detailed information regarding toxicity exposure levels, flashpoints, required safety equipment and recommended procedures for spill containment.
Another problem with the implementation of this system is that most chemicals have multiple hazards and a decision must be made as to which storage area would be most appropriate for each specific chemical. First you have to determine your priorities! When establishing a storage scheme, the number one consideration should be the flammability characteristics of the material. If the material is flammable, it should be stored in a flammable cabinet. If the material will contribute significantly to a fire (i.e., oxidizers), it should be isolated from the flammables. If there were a fire in the lab and response to the fire with water would exaggerate the situation, isolate the water reactive material away from contact with water. Next look at the corrosivity of the material, and store accordingly. Finally, consider the toxicity of the material, with particular attention paid to regulated materials. In some cases, this may mean that certain chemicals will be isolated within a storage area, for instance, a material that is an extreme poison but is also flammable, should be locked away in the flammable storage area to protect it against accidental release. There will always be some chemicals that will not fit neatly in one category or another, but with careful consideration of the hazards involved, most of these cases can be handled in a reasonable fashion.
The earlier example of a detailed storage organization based on incompatibility, is perhaps too complex for most research labs, but all labs are capable of establishing a minimum storage scheme based on hazard classes. For the safety of all personnel and to protect the integrity of the facilities, hazardous materials must be segregated.
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