Chemical Storage and Compatibility

Proper chemical storage and compatibility are essential parts of laboratory safety. Chemicals that are safe when stored separately can create a fire, explosion, toxic-gas release, excessive heat, pressure buildup, or other dangerous reaction if incompatible materials accidentally contact one another.

A laboratory chemical-storage system should therefore be based primarily on hazard classification and chemical compatibility—not simply alphabetical order.

OSHA’s nonmandatory Appendix A to the Laboratory Standard recommends separating and storing chemicals according to hazard category and compatibility, following Safety Data Sheet (SDS) and label information, and keeping incompatible materials separated during transport, storage, use, and disposal.

Proper laboratory chemical storage also involves more than chemical segregation. Container condition, shelving, secondary containment, storage cabinets, temperature, ventilation, security, inventory control, and the quantity of chemicals being stored can all affect laboratory safety.

What Is Chemical Compatibility?

Chemical compatibility describes whether chemicals can be stored or handled together without creating an unacceptable hazard if they accidentally mix or contact one another.

Two chemicals may be incompatible because their interaction could:

• Generate excessive heat.
• Cause a fire.
• Cause an explosion.
• Produce toxic or flammable gases.
• Create excessive pressure.
• Cause violent boiling or splattering.
• Produce unstable compounds.
• Accelerate decomposition.
• Damage containers or storage equipment.

Compatibility should be evaluated before chemicals are stored together, combined in secondary containment, transported together, or placed into the same waste stream.

The Safety Data Sheet, particularly information addressing stability, reactivity, handling, and storage, is an important starting point for determining appropriate storage requirements.

OSHA requires laboratories covered by 29 CFR 1910.1450 to maintain SDSs received with incoming shipments of hazardous chemicals and make them readily accessible to laboratory employees.

Do Not Store Chemicals Simply Alphabetically

Alphabetical storage may appear organized, but it can place dangerously incompatible chemicals next to one another.

For example, an alphabetical system could potentially place an oxidizer beside an organic solvent or an acid beside a chemical that releases toxic gas when acidified.

Instead, chemicals should first be separated into appropriate hazard and compatibility groups.

Alphabetical organization can then be used within compatible storage groups when appropriate.

A better general approach is:

Identify the hazard → Determine compatibility → Segregate incompatible groups → Organize within the compatible group

OSHA’s Appendix A specifically recommends separating and storing chemicals according to hazard category and compatibility.

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Chemical Storage Compatibility

There is no single segregation system appropriate for every chemical inventory. A laboratory should develop its storage arrangement around the chemicals actually present and follow manufacturer, SDS, facility, and applicable regulatory requirements.

The following categories illustrate common chemical-storage considerations.

Acids

Acids should be stored in locations and containers appropriate to their corrosive properties.

Acid storage should consider:

• Compatibility with shelving and cabinets.
• Secondary containment.
• Container condition.
• Appropriate storage height.
• Separation from incompatible bases.
• Separation from reactive metals where applicable.
• Separation from chemicals capable of producing hazardous gases when acidified.

Some acids have additional hazards and should not automatically be stored with every other acid.

For example, oxidizing acids can require separation from organic acids, combustible materials, reducing agents, and other incompatible chemicals.

This is why a storage system labeled simply “ACIDS” may not provide adequate segregation for every laboratory.

Bases

Corrosive bases should generally be separated from incompatible acids and stored in compatible containers and storage areas.

Examples may include sodium hydroxide, potassium hydroxide, and ammonium hydroxide solutions.

Storage considerations include:

• Chemical compatibility.
• Container material.
• Secondary containment.
• Protection from breakage.
• Appropriate shelving.
• Separation from acids and other incompatible substances.

A spill involving an acid and a base stored in the same secondary-containment tray could result in an uncontrolled reaction even though the original containers were separate.

Oxidizers

Oxidizing chemicals can intensify combustion or react vigorously with incompatible materials.

OSHA’s Appendix A recommends storing oxidizers, reducing agents, and fuels separately so accidental contact does not occur.

Oxidizers may require separation from:

• Flammable liquids.
• Combustible materials.
• Organic chemicals.
• Reducing agents.
• Other incompatible materials.

The specific incompatibilities depend on the chemical.

Never assume that all chemicals having the same general physical appearance can be stored together.

Flammable Liquids

Flammable liquids require controls addressing both chemical compatibility and fire hazards.

OSHA’s Appendix A recommends storing flammable chemicals in approved flammable-liquid containers and storage cabinets and maintaining a spark-free environment as appropriate. It also recommends grounding and bonding when dispensing solvents where static-charge buildup presents a hazard.

Flammable liquids should be:

• Kept away from ignition sources.
• Separated from incompatible oxidizers.
• Stored in appropriate containers.
• Kept closed when not in use.
• Stored in approved cabinets when required.
• Limited to appropriate quantities in laboratory work areas.

OSHA’s flammable-liquids standard establishes specific requirements for storage cabinets and allowable quantities. For example, a storage cabinet may contain no more than 60 gallons of Category 1, 2, or 3 flammable liquids or 120 gallons of Category 4 flammable liquids.

Actual laboratory storage must account for the applicable OSHA requirements as well as building, fire-code, facility, and authority-having-jurisdiction requirements.

Water-Reactive Chemicals

Water-reactive chemicals can produce dangerous reactions when exposed to water or moisture.

Depending on the substance, contact with water can:

• Generate flammable gas.
• Produce significant heat.
• Cause fire.
• Create corrosive products.
• Cause a violent reaction.

These materials should be stored according to their specific SDS requirements and protected from water, aqueous solutions, sprinkler discharge where specialized protection is required, and other incompatible materials as appropriate.

Employees should also consider how a water-reactive material would be managed during a spill or fire before beginning work with it.

Pyrophoric Chemicals

Pyrophoric materials can ignite spontaneously when exposed to air under certain conditions.

These chemicals require specialized storage and handling procedures based on the individual substance and its form.

Controls may include:

• Inert-atmosphere storage.
• Properly sealed containers.
• Specialized storage locations.
• Strict moisture or air exclusion.
• Appropriate fire-response materials.
• Written SOPs.
• Employee training.
• Prior approval for use.

Pyrophoric materials should not be treated as ordinary flammable chemicals simply because fire is the principal visible hazard.

Peroxide-Forming Chemicals

Certain chemicals can form potentially dangerous peroxides during storage.

OSHA’s Appendix A recommends dating peroxide-forming chemicals when they are received and again when opened, storing them away from heat and light, and using tight-fitting, nonmetal lids.

Laboratories should establish procedures for:

• Identifying peroxide-forming chemicals.
• Recording receipt and opening dates.
• Following manufacturer or institutional storage-life requirements.
• Periodic inspection or testing where appropriate.
• Proper disposal.
• Recognizing suspicious crystallization, discoloration, or other deterioration.

A container suspected of dangerous peroxide formation should not be opened, moved, scraped, or otherwise disturbed by unqualified personnel. Specialized evaluation may be necessary.

Particularly Hazardous Substances

OSHA’s Laboratory Standard requires additional consideration for particularly hazardous substances, including select carcinogens, reproductive toxins, and substances with a high degree of acute toxicity.

Depending on the substance and risk assessment, storage controls may include:

• Designated storage areas.
• Restricted access.
• Locked or secured storage.
• Secondary containment.
• Ventilated storage.
• Clear hazard identification.
• Small inventory quantities.
• Additional inventory controls.

OSHA’s Appendix A recommends storing highly hazardous chemicals in a well-ventilated and secure area designated for that purpose.

Toxic Chemicals

Toxic chemicals should be stored according to their physical properties, chemical compatibility, volatility, toxicity, and potential routes of exposure.

Highly toxic volatile chemicals may warrant additional containment or ventilated storage.

Containers should remain securely closed, and employees should consider the consequences of container failure when determining the appropriate storage location.

Corrosive Chemicals

Corrosive chemicals can damage skin, eyes, equipment, shelves, cabinets, and other chemical containers.

Storage should account for:

• Acid/base compatibility.
• Oxidizing properties.
• Container compatibility.
• Secondary containment.
• Shelf construction.
• Container size and weight.
• Safe retrieval.

Large corrosive containers should generally be positioned where employees do not need to lift them above eye or shoulder level.

 Chemical Storage Compatibility Chart

The following is a general chemical segregation guide, not a substitute for reviewing the SDS or obtaining chemical-specific compatibility information.

Important: This chart provides only general categories. Chemicals within the same category may still be incompatible with one another.

Always review the SDS, manufacturer’s instructions, laboratory SOP, and chemical-specific compatibility information before determining storage arrangements.

Examples of Incompatible Chemicals

Some incompatibilities are particularly important because accidental mixing can have severe consequences.

Examples of combinations that may require separation include:

Acids + Bases
May generate significant heat and splattering.

Acids + Cyanides
Can generate highly toxic hydrogen cyanide gas.

Acids + Sulfides
Can generate toxic hydrogen sulfide gas.

Oxidizers + Flammable or Organic Materials
Can result in rapid combustion or fire.

Water-Reactive Chemicals + Water
May generate heat, flammable gas, or violent reactions.

Strong Oxidizing Acids + Organic Materials
May produce vigorous reactions, fire, or decomposition.

These examples are not comprehensive.

A chemical should not be considered compatible simply because a particular combination does not appear on a short incompatibility list.

Chemical Storage Cabinets

Storage cabinets should be selected according to the hazards of the chemicals being stored.

Common laboratory cabinets may include:

• Flammable-liquid storage cabinets.
• Corrosive or acid-storage cabinets.
• Base-storage cabinets.
• Toxic-material storage cabinets.
• Specialized ventilated cabinets.

A cabinet’s label does not automatically make every chemical within that broad hazard category compatible with every other chemical in the cabinet.

Internal segregation may still be necessary.

For example, placing two incompatible corrosives inside the same corrosive-storage cabinet without adequate separation could still create a hazardous reaction if both containers leak.

Flammable-Liquid Storage Cabinets

OSHA establishes design and construction requirements for flammable-liquid storage cabinets under 29 CFR 1910.106.

Among other requirements, cabinets must be designed and constructed to limit internal temperature during the specified fire test and must bear conspicuous wording indicating that they contain flammable materials and should be kept away from fire. OSHA also establishes cabinet quantity limits.

Laboratories should not assume that simply placing a chemical inside a flammable cabinet addresses chemical compatibility. Oxidizers and other incompatible chemicals should not be placed there merely because cabinet space is available.

Chemical Storage Shelves

Open shelving used for chemicals should be stable and suitable for the materials being stored.

OSHA’s Appendix A recommends that open chemical-storage shelves be secured to the wall and have ¾-inch lips, with secondary containment used as necessary.

Good storage practices also include:

• Avoid overcrowding.
• Do not overload shelves.
• Keep large and heavy containers at safer retrieval heights.
• Keep chemicals away from shelf edges.
• Use compatible shelf materials.
• Protect containers from being struck or knocked over.
• Avoid storing hazardous chemicals above locations where employees routinely work.

Storage arrangements should allow employees to retrieve chemicals without unsafe reaching, climbing, or moving numerous incompatible containers.

Chemical Refrigerators and Freezers

Some chemicals require refrigerated or frozen storage.

Ordinary household refrigerators and freezers may contain electrical components capable of igniting flammable vapors and should not be assumed suitable for flammable chemical storage.

OSHA’s Appendix A recommends laboratory-grade, flammable-rated refrigerators and freezers for sealed containers of flammable liquids requiring cool storage.

Laboratory refrigerators and freezers should:

• Be appropriate for the chemicals stored.
• Be clearly identified for laboratory use.
• Not be used for food or beverages.
• Be periodically inspected.
• Be kept reasonably organized.
• Avoid incompatible chemical storage.
• Have containers appropriately labeled.

Materials should not be stored indefinitely simply because they are refrigerated.

Chemical Fume Hoods Are Not Storage Cabinets

A chemical fume hood should not ordinarily be used as a chemical-storage cabinet.

Excessive bottles and equipment can interfere with airflow and reduce the hood’s effectiveness as an exposure-control device.

OSHA’s Appendix A specifically recommends that chemicals not be stored in chemical hoods.

Chemicals actively being used for a procedure may need to remain in the hood during the operation, but unnecessary long-term storage should be avoided.

For additional information, see Chemical Fume Hood Safety.

Chemical Storage on Floors and Benchtops

Hazardous chemicals should not become permanently stored wherever convenient space happens to be available.

OSHA’s Appendix A recommends that chemicals not be stored:

• In chemical hoods.
• On floors.
• In egress areas.
• On benchtops.
• Near heat.
• In direct sunlight.

Temporary placement during active laboratory work is different from using these locations as routine chemical-storage areas.

Dedicated storage reduces the likelihood of containers being knocked over, broken, exposed to incompatible materials, or forgotten.

Chemical Storage Near Sinks and Drains

Chemical containers should be positioned so an accidental spill is not unnecessarily likely to enter a sink, floor drain, storm drain, or other environmental pathway.

Water-reactive chemicals require particular care around sinks and water sources.

Where significant liquid quantities are stored, secondary containment or other spill-control measures may be appropriate.

Chemical Container Condition

Chemical containers should be periodically inspected.

Watch for:

• Cracks.
• Leaks.
• Corrosion.
• Bulging.
• Discoloration.
• Damaged caps.
• Deteriorating seals.
• Crystallization.
• Pressure buildup.
• Damaged labels.
• Evidence of chemical attack on the container.
• Unusual deposits around the closure.

A deteriorating container should not simply be returned to the shelf.

The chemical should be evaluated and transferred, stabilized, isolated, or disposed of using procedures appropriate to the hazard.

Chemical Receiving and Procurement

Safe chemical storage begins before the chemical arrives.

OSHA’s Appendix A recommends knowing proper handling, storage, and disposal requirements before a substance is received and purchasing only the minimum quantity necessary for planned work. It also recommends review and approval of high-risk chemical purchases by the Chemical Hygiene Officer.

Before ordering a new hazardous chemical, consider:

Do we actually need it?

How much is needed?

Where will it be stored?

What chemicals is it incompatible with?

Do we have the necessary cabinet or storage equipment?

Does it require refrigeration, ventilation, security, or special containment?

How will we eventually dispose of it?

Buying a chemical without answering these questions can create a storage problem that lasts for years.

Chemical Inventory Management

An accurate chemical inventory helps prevent excessive purchasing and allows laboratories to identify chemicals that require special attention.

OSHA’s Appendix A recommends maintaining an accurate chemical inventory and disposing of or returning chemicals that are no longer needed.

A useful inventory may include:

• Chemical name.
• Manufacturer.
• Container size.
• Approximate quantity.
• Storage location.
• Date received.
• Date opened where applicable.
• Expiration or review date where applicable.
• Special hazards.
• Responsible laboratory or person.

Inventory practices should be proportionate to the laboratory’s size and hazards.

Expired, Unneeded and Deteriorating Chemicals

Laboratories should periodically identify chemicals that are:

• Expired.
• No longer needed.
• Deteriorating.
• Unidentified.
• Duplicated unnecessarily.
• Stored in damaged containers.
• Potentially unstable because of age.
• Left behind from discontinued work.

Old chemicals should not remain indefinitely simply because shelf space is available.

Some chemicals become more hazardous with age, making periodic inventory review an important safety practice rather than merely an organizational exercise.

Transporting Chemicals Within the Laboratory

Chemical compatibility also matters during transport.

OSHA’s Appendix A recommends secondary containment when transporting chemicals and break-resistant transport containers when moving chemicals outside the laboratory or between stockrooms and laboratories. It also recommends avoiding high-traffic areas where practical.

Appropriate bottle carriers, carts, trays, or other containment should be used based on the material and quantity.

Do not carry multiple incompatible chemicals together in a manner that could allow them to mix if containers break.

Chemical Waste Compatibility

Compatibility requirements continue after a chemical becomes waste.

Incompatible chemical wastes should not be mixed simply to reduce the number of waste containers.

OSHA’s Appendix A recommends storing each waste type in a compatible container and keeping incompatible waste types separate to prevent heat generation, gas evolution, or other dangerous reactions.

Employees should understand the laboratory’s waste-segregation procedures before adding anything to a waste container.

When the contents of a waste container are uncertain, do not add another chemical until compatibility has been established.

Chemical Storage and Compatibility Checklist

A basic Chemical Storage and Compatibility Checklist can include:

☐ Chemicals are organized by hazard and compatibility.

☐ Chemicals are not stored solely alphabetically without regard to compatibility.

☐ SDS storage information is available and followed.

☐ Incompatible acids and bases are adequately separated.

☐ Oxidizers are separated from flammables, combustibles, organics, and reducing agents as appropriate.

☐ Water-reactive chemicals are protected from water and incompatible materials.

☐ Pyrophoric chemicals receive appropriate specialized storage.

☐ Peroxide-forming chemicals are identified and dated.

☐ Flammable liquids are stored in appropriate containers and cabinets when required.

☐ Particularly hazardous substances receive additional controls where appropriate.

☐ Storage shelves are stable and properly secured.

☐ Containers are protected from falling.

☐ Heavy containers are stored at safe retrieval heights.

☐ Secondary containment is provided where appropriate.

☐ Incompatible chemicals do not share secondary containment.

☐ Chemicals are not routinely stored on floors.

☐ Chemicals are not stored in exit routes.

☐ Chemical fume hoods are not being used for unnecessary storage.

☐ Chemicals are protected from inappropriate heat and direct sunlight.

☐ Refrigerators and freezers are appropriate for the chemicals stored.

☐ Laboratory refrigerators are not used for food or beverages.

☐ Containers are in good condition.

☐ Chemical labels are legible.

☐ Unknown chemicals are identified or properly managed.

☐ Expired and unnecessary chemicals are periodically removed.

☐ Chemical inventory information is maintained as appropriate.

☐ Chemical waste is segregated for compatibility.

☐ Storage areas remain accessible and orderly.

☐ High-hazard chemicals receive appropriate security and access control.

Inspect Chemical Storage Regularly

Chemical storage conditions change continuously.

New chemicals arrive. Existing chemicals are consumed. Containers age. Experiments change. Employees move materials. Waste accumulates.

For this reason, chemical storage should be reviewed as part of routine Laboratory Safety Inspections.

Inspectors should pay particular attention to unusual containers and conditions rather than simply checking whether shelves look neat.

A perfectly organized shelf can still contain incompatible chemicals.

The question is not merely:

“Does this storage area look organized?”

It is:

“If one of these containers leaked or broke, what could it contact?”

That question often reveals compatibility problems that appearance alone will not.

Developing a Chemical Storage and Compatibility System

A practical laboratory chemical-storage system can follow five steps:

• Identify each chemical’s hazards.
  Review the container label, SDS, laboratory procedures, and other appropriate technical information.
• Assign an appropriate compatibility group.
  Consider flammability, corrosivity, oxidation potential, water reactivity, toxicity, instability, and chemical-specific incompatibilities.
• Separate incompatible groups.
  Use different cabinets, compartments, shelves, secondary-containment systems, or other effective means of segregation.
• Organize chemicals within compatible groups.
  Alphabetical organization may be useful at this stage.
• Inspect and maintain the system.
  Periodically review inventories, container condition, labels, storage quantities, compatibility, and chemicals that are no longer needed.

This creates a system that is both safe and practical for employees to use.

Chemical Compatibility Is Chemical-Specific

One of the most important principles of chemical storage and compatibility is that broad compatibility charts have limitations.

Terms such as acid, base, oxidizer, flammable, toxic, and reactive describe broad hazard groups. They do not tell you everything about an individual substance.

A chemical can have several hazards simultaneously.

For example, a material may be both corrosive and oxidizing. Another may be flammable and highly toxic. A third may require refrigerated storage but also be incompatible with materials normally stored in that refrigerator.

For that reason:

Never rely exclusively on the name of a storage cabinet, container color, alphabetic order, or a simplified compatibility chart.

Use the SDS and chemical-specific information to determine the proper storage requirements.

Chemical Storage and Compatibility in the Chemical Hygiene Plan

For laboratories covered by OSHA’s Laboratory Standard, chemical storage practices should coordinate with the employer’s Chemical Hygiene Plan.

The Laboratory Standard requires the employer to develop and implement a written CHP capable of protecting employees from the health hazards associated with hazardous chemicals. Employees must also be provided information about the safe handling, storage, and disposal of hazardous chemicals in their work area.

OSHA’s Appendix A expands upon this by recommending specific practices for chemical procurement, distribution, storage, inventory, transportation, and waste management.

Good chemical storage is therefore not an isolated housekeeping practice. It is part of the laboratory’s overall system for controlling chemical hazards.

Need a Chemical Storage and Compatibility Guide?

Need help organizing laboratory chemicals?

Use a Chemical Storage and Compatibility Guide to help identify chemical-storage groups, separate incompatible chemicals, evaluate storage cabinets and secondary containment, and inspect laboratory chemical-storage areas.

OSHA 29 CFR 1910.1450
Laboratory Standard

OSHA Appendix A
Chemical Hygiene Plan Guidance

OSHA 29 CFR 1910.106
Flammable Liquids