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PROPER CHEMICAL SEGREGATION

Below is an article by ScienceLab.com that has many useful recommendations with regard to hazardous chemicals and proper storage solutions. We suggest that you look at their site and compare your MSDS Sheets for more information.
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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.

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.

Chemical Storage Practices

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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 :

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.

The above information with the permission of ScienceLab.com, and we encourage you to visit their web site.

ScienceLab has a vast array of chemical information on their web site and if you use, purchase, or store chemicals or chemical related equipment, we highly suggest you click the link above and review their knowledge base and chemical products on their web site.

HINT #2 - Check references! For a capital expense like a prefabricated building... Always err on the side of Safety! Request reference that are 5-10 years old.