Chemical Storage Safety Guidance

Poor or incorrect chemical storage practices can lead to inadvertent reactions between incompatible materials with the potential to cause harm, fire or even explosions.

All chemicals should be stored in such a manner as to prevent incompatible materials from being accidentally mixed together in the event of the breakage of one or more containers in the storage area, or to prevent the formation and build-up of reactive vapours. The correct storage of chemicals within storage areas / stock rooms, workshops and laboratories is an on-going problem which can sometimes be complex and potentially confusing. The overall purpose of correct storage is to maintain control over the chemicals so that they can be both stored and retrieved safely.

COSHH forms and risk assessments must consider the storage of substances as well as their use

Many chemicals, including waste chemicals awaiting safe disposal, have special storage requirements with temperature, time, or security restrictions and practical problems can arise because of the number of separations that could be desirable. Correct storage must address the compatibility issues of flammable substances, unstable materials, highly reactive chemicals and vapours of highly toxic materials.

Safe storage of chemicals can be achieved by arranging the materials to provide separation based on their chemical properties. This requires planning and will involve, an inventory list, accurate labelling, an appreciation of chemical incompatibilities and a range of suitable containers and storage facilities.

In essence, the most important reasons for proper chemical storage are:

1. to provide for effective management of chemicals
2. to lessen the risk of fire
3. to prevent accidental mixing in emergencies
4. to minimise exposure to corrosive and toxic chemicals
5. to comply with relevant statutory security obligations

Accidents resulting from poor chemical storage techniques are preventable and appendix 1 lists some common examples of improper storage practices to avoid.

General Considerations

Safe storage of chemicals must begin with identification of the chemicals to be stored and their intrinsic hazardous properties. Since many chemicals have several hazards, which may vary in degree of severity, depending on quantity and concentration, it is not always straight forward to determine what protection is needed for safe storage and where best to store a particular chemical. However, typical storage considerations may include temperature, ignition control, ventilation, segregation and identification.

Separation (i.e. use of distance), segregation (i.e. use of a physical boundary) or isolation is recommended depending upon the severity of hazard, total quantities stored, and the size, break resistance and durability of individual containers (i.e. fragility of glass bottles, perforation or degradation of plastic containers, and corrosion or puncture of metal containers). Hence, the physical composition and even the size of storage containers may also affect the need for special storage practices and safety procedures.

It should be noted that ventilation is needed for chemicals and their containers which may release dangerous or damaging quantities of vapours or gases that are flammable, corrosive, irritating or toxic. Ventilated storage is particularly important for those substances classed as fuming or highly volatile.

Ventilation should be by air extraction from the storage area to an external exhaust at a safe distance, at least 3 m, from openings into the building. This can sometimes be achieved via appropriate connection to an adjacent fume cupboard extraction system (consult the LEV Duty Appointed Person). Highly odorous chemicals should also be stored in a well-ventilated area; a ventilated cabinet is preferable.

In general the storage of chemicals within fume cupboards is strongly discouraged, unless it is for the reaction at hand, as materials stored in the fume cupboard can adversely affect the containment provided and increase the risk of accidental spillage and /or contact with incompatible substances.

Highly toxic chemicals (such as cyanide, cacodylic acid), shock-sensitive chemicals (such as solid sodium azide or picric acid), and habit-forming chemicals (amyl nitrite) must be stored in locked cabinets to prevent theft.

Peroxide-forming chemicals and those that may become shock-sensitive with long-term storage should be stored separately and labelled with date of receipt, date of opening and disposal date. Peroxide-forming chemicals should be stored in a cool, dark, dry place.

Flammable liquids should be stored in clearly labelled, flammable-liquid cabinets (flame-resistant metal cabinets) which are at least:

• of 30 minutes fire resisting construction (BS EN 14470-1:2004/HSG51)
• robust enough to withstand foreseeable accidental damage
• able to retain spillage equivalent to 110% of the contents of the largest container(bunded)
• appropriatelylabelled to indicate contents and signed to indicate the nature of the hazard
• sited so as to ensure adequate separation of incompatibles, and away from sources ofheat or ignition, as necessary, and away from hazardous areas and emergency escaperoutes

It is recommended that the maximum quantities that may be stored in such cabinets and bins are no more than 50 litres for extremely, highly flammable and those flammable liquids with a flashpoint below the maximum ambient temperature of the workroom/working area; and no more than 250 litres for other flammable liquids with a higher flashpoint of up to 55°C. – With any greater quantities requiring a specific risk assessment and would need approving via the H&S service

Empty flammable substance containers, unless completely free of liquid or vapour must also be kept in the highly flammable liquids store and must be securely closed until appropriate disposal is arranged or the containers have been washed out and aired to dry.

Hazardous substances cabinets should be designated for, and restricted to, a particular class of substance. In particular, other substances should not be stored with highly flammable substances. No other combustible material, including packaging, should be kept in, or within 1 metre of, a hazardous substances cabinet.

Every storage area should have emergency, and where necessary, evacuation procedures in case of a leak, spill or fire within the room. It may be necessary to consider incidents in adjacent parts of the premises, which may affect the storage, if necessary, consult the Fire Safety Officer for further guidance.

Where necessary, adequate drainage should be provided to deal with water used for fire protection, firefighting or post fire cooling (acetylene cylinders), to minimise environmental damage. Interceptors or special drainage systems may be necessary to minimise the risk of contamination of watercourses.

Storage areas and buildings, rooms, cupboards and bins should be adequately maintained.

The location of frequently used chemical storage areas should be based on consideration of safety in travel to the storage area and transport of chemicals to and from storage.

Chemicals stored at the bench or other work areas should be those that are used frequently and quantities should be limited to the minimum that is convenient.

Open Air Stores

These must have the means of controlling a spillage. This may be an impervious sill or low bund, typically 150 mm high and big enough to hold 110% of the contents of the largest container. The alternative is to drain the area to a safe place, such as a remote sump or separator. Absorbent granules or another means of clearing up small spills must be provided but it should be noted that some granules such as clay are not suitable for certain chemicals e.g. hydrofluoric acid. Care must be taken to ensure that any absorbent materials used are compatible with the chemicals being stored.

The surface of the storage area should be sloped so that any spillage does not accumulate around the containers butcan drain to a safe area or to a sump / interceptor. There should be no combustible materials (including vegetation) in the storage area or within 1m of the sill or bund wall.

Stores in Buildings

Where there are centralised storage areas / stock rooms the following requirements exist:

• Store rooms / buildings should be adequately ventilated to disperse vapour from any leakage or spillage and should have at least five air changes per hour
• Means of containing spillage should be provided for example a sloping floor or a 150 mm sill across door openings
• Ramps may need to be provided for ease of access for wheeled trolleysetc.
• The floor should be impermeable and inert with respect to the liquids stored
• Any heating and lighting provided in the store should not be able to act as a source of ignition. There should be no possibility of flammable vapour being ignited by hot surfaces and adequate ventilation of the store must bemaintained
• External storage buildings, whether or not they are fire-resisting structures, should have a lightweight roof to act as explosion relief. For internal stores, relief panels may be provided in one or more walls, providing the relief can vent to a safe place
• All stores should be operated so that the risk of spillage is minimised. They should not normally be used for dispensing operations, nor should other materials be kept in them.
• Any area where an explosive atmosphere could exist or be generated (i.e. as a result of a spillage) must be assessed with respect to the Dangerous Substances and Explosive Atmosphere Regulations (DSEAR) and zoned where appropriate.

Refrigerator Storage (Fridges and Freezers)

Refrigerator temperatures are often higher than the flash points of extremely / highly flammable liquids and ignition sources are readily available inside the storage compartment of an unmodified domestic type refrigerator. Also the compressor and its circuits are typically located at the bottom of the units, where vapours from flammable liquid spills or leaks of liquid (or vapour) may easily accumulate.

Furthermore should a refrigerator malfunction the internal temperature can rise above the flash point of most if not all flammable liquids aka flammable solvents, therefore…..

Flammable liquids must not be stored in ordinary domestic refrigerators.

Flammable liquids must only be stored in fridges and freezers expressly designed or modified for the purpose, i.e. those which have all ignition sources removed.

Some domestic type refrigerators can be modified to become internally ‘explosion-safe’ aka ‘spark- free’ aka ‘spark-proof’ permitting storage of flammable liquids. To avoid confusion these refrigerators will be hereafter referred to as internally ‘spark-free’. The modifications needed include relocation of manual temperature controls to the exterior of the storage compartment, removal of light switches and assemblies, replacing mechanical door latches with magnetic door gaskets and sealing any holes left. The purpose of these modifications is to eliminate ignition of vapours inside the storage compartment by removing ignition sources within the compartment. Ideally, labs requiring refrigerator storage for flammable liquids should purchase commercial ‘spark –free’ models that require no modification.

Modifications may only be conducted by qualified electricians who will certify the safety of the work.

Under no circumstances should lab workers attempt to perform modifications themselves.

Note: ‘explosion-proof’ refers to refrigeration equipment that has been designed to protect against ignition of flammable vapours both inside and outside the storage compartment (i.e. it is ATEX rated).

Internally ‘spark-free’ refrigerators are NOT ‘explosion-proof’ and thereby NOT ATEX rated

If refrigerators are not internally ‘spark free’ (or ‘explosion-proof’), they must be labelled ‘Caution: Not approved for flammable liquid storage’ or similar. Flammable liquids must not be stored in cold rooms that do not have explosion-proof wiring and fixtures. Such storage facilities pose explosion hazards because the various control switches and defroster heaters can spark and ignite flammable vapours.

Chemicals stored in refrigerators or cold rooms should be sealed and appropriately labelled, including the name of the person who stored the material.

Food and drink must not be stored in a refrigerator used for chemical storage. The refrigerator should be labelled ‘Food and Drink Must NOT Be Stored in this Refrigerator’ or equivalent. Refrigerators used for food should be marked ‘Food and Drink Only’ or equivalent and must not be in the work area.

Workshop Storage

Most workshops will usually not have large quantities of chemicals, indeed a workshop is not the appropriate location for the bulk storage of hazardous chemicals.
Typically a workshop might contain:

•  Solvents such as:
  • degreasing agents
  • paraffin (kerosene)
  • methylated spirits
  • paint thinners
• Aerosol cans, often pressurised by butane
• Petrol, diesel or other fuels in small quantities.
• Solvent based paints
• Acids for cleaning, de-scaling or de-rusting etc.
• Gas cylinders (see: Compressed Gases Policy and Guidance on safe use and storage on the H&S internal website).

Many workshops will only contain small quantities of hazardous chemicals and can maintain adequate segregation and safe storage by following the guidance in this document and through the application of good practice and common sense:

• Minimise the amount of chemicals stored in the worksho
• Keep all toxic chemicals in cupboards and secure where appropriate
• Do not store or use acids with bleach i.e. solutions containing hypochlorite
• Avoid using any agents containing hydrofluoric acid which is particularly toxic and willrequire specialised storage
• The total quantity of flammable solvent on the open bench should not exceed onelitre
• Store all other bulk flammable solvents in a metal solvent cabinet, the grand total stored in a workshop must not exceed 50 litres.
• Do not store any flammable solvents in close proximity to any source of ignition including:
  • Open (naked) flames such as burners, heaters, glass blowing / cutting / welding torches or forge benches.
  • o Grinding wheels, hand held or fixed
  • o Electric heaters or heat guns
  • o Electric arc welders
  • o Electrical tools and equipment
  • o Sources of static electricity

It should be noted that cylinders of acetylene represent a significant risk of explosion in a fire and it is standard emergency services practice to hose them down with water for 24 hours following a fire, before they can be moved. Therefore it may be worth giving some consideration when locating acetylene cylinders as to drainage available and what the consequences would be to the surrounding areas.

Note: It would be expected that most workshops can comply with this guidance without theneed for a plethora of specialised storage cabinets, by minimising the quantities held and by spatial separation of incompatible substances.

The risk associated with incompatible chemicals coming into contact must be avoided wherever chemicals are handled or stored as 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 vapours which can rapidly travel outward to an ignition source, thus creating a dangerous fire situation. Reaction products may also release toxic vapours capable of overcoming nearby personnel. Finally, even non-hazardous vapours 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. (ask the H&S service for guidance on oxygen depletion)

The most common chemical storage practice is that of simply storing chemicals in alphabetical order on shelves. This often results in incompatible chemicals being stored together e.g. alphabetical arrangement could result in hydrogen peroxide (a strong oxidizer) being stored next to hydrazine (a very strong reducer). Chemicals should not be stored alphabetically unless they have first been separated into their hazard classes.

There are no absolute rules on how many classes of chemicals should be segregated. The degree of segregation will depend upon the risk. However, isolation of chemicals into the basic hazard classes will eliminate most accidental adverse reactions that may occur due to breakages or leakages in storage areas (table available to download below).