Adapted from 3rd edition, Encyclopaedia of Occupational Health and Safety
Before a new hazardous substance is received for storage, information concerning its correct handling should be provided to all users. Planning and maintaining of storage areas are necessary to avoid material losses, accidents and disasters. Good housekeeping is essential, and special attention should be paid to incompatible substances, suitable location of products and climatic conditions.
Written instructions of storage practices should be provided, and the chemicals’ material safety data sheets (MSDSs) should be available in storage areas. Locations of the different classes of chemicals should be illustrated in a storage map and in a chemical register. The register should contain the maximum allowed quantity of all chemical products and the maximum allowed quantity of all chemical products per class. All substances should be received at a central location for distribution to the storerooms, stockrooms and laboratories. A central receiving area is also helpful in monitoring substances that may eventually enter the waste-disposal system. An inventory of substances contained in the storerooms and stockrooms will give an indication of the quantity and nature of substances targeted for future disposal.
Stored chemicals should be examined periodically, at least annually. Chemicals with expired shelf lives and deteriorated or leaking containers should be disposed of safely. A “first in, first out” system of keeping stock should be used.
The storage of dangerous substances should be supervised by a competent, trained person. All workers required to enter storage areas should be fully trained in appropriate safe work practices, and a periodic inspection of all storage areas should be carried out by a safety officer. A fire alarm should be situated in or near the outside of the storage premises. It is recommended that persons should not work alone in a storage area containing toxic substances. Chemical storage areas should be located away from process areas, occupied buildings and other storage areas. In addition, they should not be in proximity of fixed sources of ignition.
Labelling and Relabelling Requirements
The label is the key to organizing chemical products for storage. Tanks and containers should be identified with signs indicating the name of the chemical product. No containers or cylinders of compressed gases should be accepted without the following identifying labels:
- identification of contents
- description of principal hazard (e.g., flammable liquid)
- precautions to minimize hazards and prevent accidents
- correct first aid procedures
- correct procedures for cleaning up spills
- special instructions to medical personnel in case of an accident.
The label may also offer precautions for correct storage, such as “Keep in a cool place” or “Keep container dry”. When certain dangerous products are delivered in tankers, barrels or bags and repackaged at the workplace, each new container should be relabelled so that the user will be able to identify the chemical and recognize the risks immediately.
Explosive Substances
Explosive substances include all chemicals, pyrotechnics and matches which are explosives per se and also those substances such as sensitive metallic salts which, by themselves or in certain mixtures or when subject to certain conditions of temperature, shock, friction or chemical action, may transform and undergo an explosive reaction. In the case of explosives, most countries have stringent regulations regarding safe storage requirements and precautions to be taken in order to prevent theft for use in criminal activities.
The storage places should be situated far away from other buildings and structures so as to minimize damage in case of an explosion. Manufacturers of explosives issue instructions as to the most suitable type of storage. The storerooms should be of solid construction and kept securely locked when not in use. No store should be near a building containing oil, grease, waste combustible material or flammable material, open fire or flame.
In some countries there is a legal requirement that magazines should be situated at least 60 m from any power plant, tunnel, mine shaft, dam, highway or building. Advantage should be taken of any protection offered by natural features such as hills, hollows, dense woods or forests. Artificial barriers of earth or stone walls are sometimes placed around such storage places.
The storage place should be well ventilated and free from dampness. Natural lighting or portable electric lamps should be used, or lighting provided from outside the storehouse. Floors should be constructed of wood or other non-sparking material. The area surrounding the storage place should be kept free of dry grass, rubbish or any other material likely to burn. Black powder and explosives should be stored in separate storehouses, and no detonators, tools or other materials should be kept in an explosive store. Non-ferrous tools should be used for opening cases of explosives.
Oxidizing Substances
Oxidizing substances provide sources of oxygen, and thus are capable of supporting combustion and intensifying the violence of any fire. Some of these oxygen suppliers give off oxygen at storage-room temperature, but others require the application of heat. If containers of oxidizing materials are damaged, the contents may mix with other combustible materials and start a fire. This risk can be avoided by storing oxidizing materials in a separate storage place. However, this practice may not always be available, as, for example, in dock warehouses for goods in transit.
It is dangerous to store powerful oxidizing substances near liquids that even have a low flash point or even slightly flammable materials. It is safer to keep all flammable materials away from a place where oxidizing substances are stored. The storage area should be cool, well ventilated and of fire-resisting construction.
Flammable Substances
A gas is deemed to be flammable if it burns in the presence of air or oxygen. Hydrogen, propane, butane, ethylene, acetylene, hydrogen sulphide and coal gas are among the most common flammable gases. Some gases such as hydrogen cyanide and cyanogen are both flammable and poisonous. Flammable materials should be stored in places which are cool enough to prevent accidental ignition if the vapours mix with the air.
Vapours of flammable solvents may be heavier than air and may move along the floor to a distant ignition source. Flammable vapours from spilled chemicals have been known to descend into stairwells and elevator shafts and ignite at a lower storey. It is therefore essential that smoking and open flames be prohibited where these solvents are handled or stored.
Portable, approved safety cans are the safest vessels for storing flammables. Quantities of flammable liquids greater than 1 litre should be stored in metal containers. Two-hundred-litre drums are commonly used to ship flammables, but are not intended as long-term storage containers. The stopper should be removed carefully and replaced by an approved pressure-relief vent to avoid increased internal pressure from heat, fire or exposure to sunlight. When transferring flammables from metal equipment, the worker should use an enclosed transfer system or have adequate exhaust ventilation.
The storage area should be situated away from any source of heat or fire hazard. Highly flammable substances should be kept apart from powerful oxidizing agents or from materials which are susceptible to spontaneous combustion. When highly volatile liquids are stored, any electric light fittings or apparatus should be of certified flameproof construction, and no open flames should be permitted in or near the storage place. Fire extinguishers and absorbent inert materials, such as dry sand and earth, should be available for emergency situations.
The walls, ceilings and floors of the storage room should consist of materials with at least a 2-hour fire resistance. The room should be fitted with self-closing fire doors. The storage-room installations should be electrically grounded and periodically inspected, or equipped with automatic smoke- or fire-detection devices. Control valves on storage vessels containing flammable liquids should be clearly labelled, and pipelines should be painted with distinctive safety colours to indicate the type of liquid and the direction of flow. Tanks containing flammable substances should be situated on ground sloping away from the main buildings and plant installations. If they are on level ground, protection against fire spread can be obtained by adequate spacing and the provision of dykes. The dyke capacity should preferably be 1.5 times that of the storage tank, as a flammable liquid may be likely to boil over. Provision should be made for venting facilities and flame arrestors on such storage tanks. Adequate fire extinguishers, either automatic or manual, should be available. No smoking should be allowed.
Toxic Substances
Toxic chemicals should be stored in cool, well ventilated areas out of contact with heat, acids, moisture and oxidizing substances. Volatile compounds should be stored in spark-free freezers (–20 °C) to avoid evaporation. Because containers may develop leaks, storerooms should be equipped with exhaust hoods or equivalent local ventilation devices. Open containers should be closed with tape or other sealant before being returned to the storeroom. Substances which can react chemically with each other should be kept in separate stores.
Corrosive Substances
Corrosive substances include strong acids, alkalis and other substances which will cause burns or irritation of the skin, mucous membranes or eyes, or which will damage most materials. Typical examples of these substances include hydrofluoric acid, hydrochloric acid, sulphuric acid, nitric acid, formic acid and perchloric acid. Such materials may cause damage to their containers and leak into the atmosphere of the storage area; some are volatile and others react violently with moisture, organic matter or other chemicals. Acid mists or fumes may corrode structural materials and equipment and have a toxic action on personnel. Such materials should be kept cool but well above their freezing point, since a substance such as acetic acid may freeze at a relatively high temperature, rupture its container and then escape when the temperature rises again above its freezing point.
Some corrosive substances also have other dangerous properties; for example, perchloric acid, in addition to being highly corrosive, is also a powerful oxidizing agent which can cause fire and explosions. Aqua regia has three dangerous properties: (1) it displays the corrosive properties of its two components, hydrochloric acid and nitric acid; (2) it is a very powerful oxidizing agent; and (3) application of only a small amount of heat will result in the formation of nitrosyl chloride, a highly toxic gas.
Storage areas for corrosive substances should be isolated from the rest of the plant or warehouses by impervious walls and floor, with provision for the safe disposal of spillage. The floors should be made of cinder blocks, concrete that has been treated to reduce its solubility, or other resistant material. The storage area should be well ventilated. No store should be used for the simultaneous storage of nitric acid mixtures and sulphuric acid mixtures. Sometimes it is necessary to store corrosive and poisonous liquids in special types of containers; for example, hydrofluoric acid should be kept in leaden, gutta percha or ceresin bottles. Since hydrofluoric acid interacts with glass, it should not be stored near glass or earthenware carboys containing other acids.
Carboys containing corrosive acids should be packed with kieselguhr (infusorial earth) or other effective inorganic insulating material. Any necessary first-aid equipment such as emergency showers and eyewash bottles should be provided in or immediately close to the storage place.
Water-reactive Chemicals
Some chemicals, such as sodium and potassium metals, react with water to produce heat and flammable or explosive gases. Certain polymerization catalysts, such as alkyl aluminium compounds, react and burn violently on contact with water. Storage facilities for water-reactive chemicals should not have water in the storage area. Non-water automatic sprinkler systems should be employed.
Legislation
Detailed legislation has been drawn up in many countries to regulate the manner in which various dangerous substances may be stored; this legislation includes the following specifications:
- type of building, its location, the maximum amounts of various substances that may be stored in one place
- type of ventilation required
- precautions to be taken against fire, explosion and the release of dangerous substances
- type of lighting (e.g., flameproof electrical equipment and light fixtures when explosive or flammable materials are stored)
- number and location of fire exits
- security measures against entry by unauthorized persons and against theft
- labelling and marking of storage vessels and pipelines
- warning notices to workers as to the precautions to be observed.
In many countries there is no central authority concerned with the supervision of the safety precautions for the storage of all dangerous substances, but a number of separate authorities exist. Examples include mine and factory inspectorates, dock authorities, transport authorities, police, fire services, national boards and local authorities, each of which deals with a limited range of dangerous substances under various legislative powers. It is usually necessary to obtain a licence or permit from one of these authorities for the storage of certain types of dangerous substances such as petroleum, explosives, cellulose and cellulose solutions. The licensure procedures require that storage facilities comply with specified safety standards.