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 Incompatibliy

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.

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
• Highly Reactives
  - acids
  - bases
• 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.