Safe Storage of Laboratory Chemicals

The purpose of this section is to identify and classify hazardous chemicals which are commonly found in the research environment. Once identified, the initiative is established to provide the proper storage, handling, use and, when needed, removal of these hazardous substances.

Many of the storage requirements presently recommended have been learned through adverse experience and incorporated into codes and regulations. Certain of these regulations, specifically those related to storage and handling of carcinogens, are not to be ignored. Others are more in the form of recommended practices. Storage guidelines are included for materials that are flammable, oxidizers, corrosive, water reactive, explosive and highly toxic. The specific Material Safety Data Sheet (MSDS) should always be consulted when doubts arise concerning chemical properties and associated hazards.

1. 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.

2. 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-, iso-)			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.

3. Recommendations For Storage of Laboratory Chemicals

In addition to segregated storage of incompatible materials, the following general suggestions for safe storage of chemicals in the laboratory should be implemented. Specific recommendations for each class of chemicals will be made in the appropriate sections.

• The quantities of chemicals that are stored within a laboratory should be minimized, as specified by NFPA 45 and OSHA. Many authorities recommend that the NFPA guidelines for maximum quantities and sizes of containers should be reduced to one-half or even one-third of the recommended values.
  
  
• Bulk quantities of chemicals (i.e., larger than one-gallon) must be stored in a separate storage area. Transfer of flammable liquid from 5 gallon or larger metal containers may not be done in the laboratory.
  
  
• Chemicals must be stored at an appropriate temperature and humidity level. This can be especially problematic in hot, humid climates. As a rule, chemicals should not be stored near heat sources, such as steam pipes or laboratory ovens. Chemicals should never be stored in direct sunlight.
  
  
• Chemicals should be dated when received and when opened. If the chemical is one that degrades in quality or becomes unsafe after prolonged storage, the shelf-life expiration date should also be included.
  
  
• Visual inspection of the material and its container should be conducted routinely. Indications for disposal include:
  • cloudiness in liquids
  • material changing color
  • evidence of liquids in solids or solids in liquids
  • "puddling" of material around outside of container
  • pressure build-up within bottle
  • obvious deterioration of container

  
  

• Chemicals should not be routinely stored on the benchtops. In such locations they are unprotected from exposure and participation in a fire situation and are also more readily knocked over. Each chemical should have a specific storage area and be returned there after use. Large quantities of flammable materials should not be stored in the laboratory. Only the amounts needed should be kept on benchtops, the remainder should be kept in flammable storage cabinets.
  
  
• Laboratory shelves should have a raised lip along the outer edge to prevent containers from falling. Never allow the container to hang off the edge of the shelf! Liquid or corrosive chemicals should never be stored on shelves above eye-level. Glass containers should not touch each other on the shelves. Secondary containers or trays should be used for chemical storage whenever possible to minimize the flow of material should a spill or rupture occur. Round bottom flasks should always be supported properly in cork rings or by other means to keep them from tipping.
  
  
• Adequate security must be provided so that unauthorized personnel do not have access to hazardous materials.
  
  
• Chemicals must never be stored on the floor, not even temporarily!
  
  
• Chemicals that are no longer to be used for research purposes should be properly disposed of or given to another research group that has a use for it.

• Flammable materials must never be stored in domestic-type refrigerators. Only explosion-proof or flammable material refrigerators should be used for storage of these chemicals within a laboratory environment.
  
  
• All containers stored within the refrigerator should be tightly capped to keep vapors from interacting with each other and to alleviate "smell" problems. Flasks with cork, rubber or glass stoppers should be avoided because of the potential for leaking. All containers stored in the refrigerator must be properly labeled.
  
  
• Inventory the materials in your refrigerator frequently to avoid overcrowding with materials that have long since been forgotten. Also make it a point to defrost your refrigerator occasionally so that chemicals do not become trapped in unique ice formations!
  
  
• Before flammable materials are stored in a refrigerator, it should be determined if keeping the material chilled will serve any purpose. No benefit is derived from refrigerating a chemical that has a flash point below the temperature of the refrigerator. Never store peroxide formers (i.e., ether) in a refrigerator!

• Fume hoods should not be used as general storage areas for chemicals. This may seriously impair the ventilating capacity of the hood.
  
  
• Gas cylinders must be securely strapped to a permanent structure (wall, lab bench, etc.). When they are not in use they should be capped off.
  
  
• On termination, graduation or transfer of any laboratory personnel, all hazardous materials must be properly disposed of, or arrangements made to transfer them to the laboratory supervisor.

Copyright © 1996 by College of Science, Texas A&M University