Flammable Materials

Flammable materials

Flammable and combustible liquids:

Flammable and combustible liquids are liquids that can burn. They are classified, or grouped, as either flammable or combustible by their flash points. Generally speaking, flammable liquids will ignite (catch on fire) and burn easily at normal working temperatures. Combustible liquids have the ability to burn at temperatures that are usually above working temperatures.

There are several specific technical criteria and test methods for identifying flammable and combustible liquids. Under the Workplace Hazardous Materials Information System (WHMIS) 1988, flammable liquids have a flash point below 37.8°C (100°F). Combustible liquids have a flash point at or above 37.8°C (100°F) and below 93.3°C (200°F).

Flammable and combustible liquids are present in almost every workplace. Fuels and many common products like solvents, thinners, cleaners, adhesives, paints, waxes and polishes may be flammable or combustible liquids. Everyone who works with these liquids must be aware of their hazards and how to work safely with them.

Flash point

the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with air near the surface of the liquid. The flash point is normally an indication of susceptibility to ignition.

The flash point is determined by heating the liquid in test equipment and measuring the temperature at which a flash will be obtained when a small flame is introduced in the vapor zone above the surface of the liquid.


Combustible liquid: any liquid having a flash point at or above 100ºF (37.8ºC).

Combustible liquids shall be divided into two classes as follows:

  1. Class II liquids shall include those with flash points at or above 100ºF (37.8ºC) and below 140ºF (60ºC), except any mixture having components with flash points of 200ºF (93.3ºC) or higher, the volume of which make up 99 percent or more of the total volume of the mixture.
  2. Class III liquids shall include those with flash points at or above 140ºF (60ºC). Class III liquids are subdivided into two sub classes:
    • Class IIIA liquids shall include those with flash points at or above 140ºF (60ºC) and below 200ºF (93.3ºC), except any mixture having components with flash points of 200ºF (93.3ºC), or higher, the total volume of which make up 99 percent or more of the total volume of the mixture.
    • Class IIIB liquids shall include those with flash points at or above 200ºF (93.3ºC). This section does not regulate Class IIIB liquids. Where the term “Class III liquids” is used in this section, it shall mean only Class IIIA liquids.

When a combustible liquid is heated to within 30ºF (16.7ºC) of its flash point, it shall be handled in accordance with the requirements for the next lower class of liquids.

Flammable liquid: any liquid having a flash point below 100ºF (37.8ºC), except any mixture having components with flash points of 100ºF (37.8ºC) or higher, the total of which make up 99 percent or more of the total volume of the mixture. Flammable liquids shall be known as Class I liquids. Class I liquids are divided into three classes as follows:

  1. Class IA shall include liquids having flash points below 73ºF (22.8ºC) and having a boiling point below 100ºF (37.8ºC).
  2. Class IB shall include liquids having flash points below 73ºF (22.8ºC) and having a boiling point at or above 100ºF (37.8ºC).
  3. Class IC shall include liquids having flash points at or above 73ºF (22.8ºC) and below 100ºF (37.8ºC).

It should be mentioned that flash point was selected as the basis for classification of flammable and combustible liquids because it is directly related to a liquid’s ability to generate vapor, i.e., its volatility. Since it is the vapor of the liquid, not the liquid itself that burns, vapor generation becomes the primary factor in determining the fire hazard. The expression “low flash – high hazard” applies. Liquids having flash points below ambient storage temperatures generally display a rapid rate of flame spread over the surface of the liquid, since it is not necessary for the heat of the fire to expend its energy in heating the liquid to generate more vapor.

The above definitions for classification of flammable and combustible liquids are quite complex. The diagram below should aid in their understanding.

Classes of Flammable and Combustible Liquids as Defined by 29 CFR 1910.106

Liquid itself burn:

Flammable and combustible liquids themselves do not burn. It is the mixture of their vapours and air that burns. Gasoline, with a flash point of -40°C (-40°F), is a flammable liquid. Even at temperatures as low as -40°C (-40°F), it gives off enough vapour to form a burnable mixture in air. Phenol is a combustible liquid. It has a flash point of 79°C (175°F), so it must be heated above that temperature before it can be ignited in air.

Flammable or explosive limits:

A material’s flammable or explosive limits also relate to its fire and explosion hazards. These limits give the range between the lowest and highest concentrations of vapour in air that will burn or explode.

The lower flammable limit or lower explosive limit (LFL or LEL) of gasoline is 1.4 percent; the upper flammable limit or upper explosive limit (UFL or UEL) is 7.6 percent. This means that gasoline can be ignited when it is in the air at levels between 1.4 and 7.6 percent. A concentration of gasoline vapor in air below 1.4 percent is too “lean” to burn. Gasoline vapor levels above 7.6 percent are too “rich” to burn. Flammable limits, like flash points however, are intended as guides not as fine lines between safe and unsafe.

Auto ignition Temperature:

A material’s auto ignition or ignition temperature is the temperature at which a material self-ignites without any obvious sources of ignition, such as a spark or flame.

Most common flammable and combustible liquids have auto ignition temperatures in the range of 300°C (572°F) to 550°C (1022°F). Some have very low auto ignition temperatures. For example, ethyl ether has an auto ignition temperature of 160°C (356°F) and its vaporous have been ignited by hot steam pipes. Serious accidents have resulted when solvent-evaporating ovens were heated to temperatures above the auto ignition temperature of the solvents used. Auto ignition temperatures, however, are intended as guides, not as fine lines between safe and unsafe. Use all precautions necessary.

Good ventilation important:

Well-designed and maintained ventilation systems remove flammable vapours from the workplace and reduce the risk of fire and health problems.

The amount and type of ventilation needed to minimize the hazards of flammable and combustible liquid vapours depend on such things as the kind of job, the kind and amount of materials used, and the size and layout of the work area.

An assessment of the specific ways flammable and combustible liquids are stored, handled, used and disposed of is the best way to find out if existing ventilation controls (and other hazard control methods) are adequate.

Some workplaces may need a complete system of hoods and ducts to provide acceptable ventilation. If flammable vapours are likely to condense, the ducts should have welded joints. Other workplaces may only require a single, well-placed exhaust fan. Use non-ferrous fan blades and shrouds (housing), and explosion-proof electrical equipment in ventilation systems for these liquids. Regular cleaning of the ducts, filters, plenums, etc. will decrease the severity of any fires and will reduce the likelihood of spontaneous combustion if some self-heating material is present. Ventilation equipment used to handle solvent vaporous should meet the relevant fire code requirements.

If the ventilation keeps vapour levels below the occupational exposure limit of a chemical, usually there is little risk of fire or explosion. Vapour levels harmful to people are, in most cases, much below the lowest concentration of vapour in air that can burn. For example, toluene has a workplace exposure limit of 20 ppm [50 parts of toluene per million parts of air or 0.005 percent] (ACGIH 2008 TLVs & BEIs) in many jurisdictions. This is far below the lower flammable limit (LFL) for toluene, which is 12,000 ppm (1.2 percent).

In baking and drying ovens, enclosed air-drying spaces, ventilation duct work or other enclosures where workers are not normally exposed to the vapour, keep vapour levels to 20 percent or less of the LFL.

Good storage area :

Store flammable and combustible liquids in areas that are:

  • Storage of Flammable liquids shall be in NFPA approved flammable storage lockers or in low value structures at least 50 feet from any other structure. Do not store other combustible materials near flammable storage areas or lockers.
  • Bulk drums of flammable liquids must be grounded and bonded to containers during dispensing.
  • Portable containers of gasoline or diesel are not to exceed 5 gallons.
  • Safety cans used for dispensing flammable or combustible liquids shall be kept at a point of use.
  • Appropriate fire extinguishers are to be mounted within 75 feet of outside areas containing flammable liquids, and within 10 feet of any inside storage area for such materials.
  • Storage rooms for flammable and combustible liquids must have explosion-proof light fixtures.
  • Bulk storage of gasoline or diesel are kept in above ground tanks. Tank areas are diked to contain accidental spills. Tanks shall be labeled IAW NFPA guidelines. All tank areas shall be designated no smoking – no hot work – no open flame areas.
  • No flames – hot work or smoking is be permitted in flammable or combustible liquid storage areas.
  • The maximum amount of flammable liquids that may stored in a building are 20 gallons of Class IA liquids in containers100 gallons of Class IB, IC, II, or III liquids in containers500 gallons of Class IB, IC, II, or III liquids in a single portable tank.
  • Flammable liquid transfer areas are to be separated from other operations by distance or by construction having proper fire resistance.
  • When not in use flammable liquids shall be kept in covered containers.
  • Class I liquids may be used only where there are no open flames or other sources of ignition within the possible path of vapor travel.
  • Flammable or combustible liquids shall be drawn from or transferred into vessels, containers, or portable tanks within a building only through a closed piping system, from safety cans, by means of a device drawing through the top, or from a container or portable tanks by gravity through an approved self-closing valve. Transferring by means of air pressure on the container or portable tanks shall be prohibited.
  • Maintenance and operating practices shall be in accordance with established procedures which will tend to control leakage and prevent the accidental escape of flammable or combustible liquids. Spills shall be cleaned up promptly.
  • Combustible waste material and residues in a building or unit operating area shall be kept to a minimum, stored in covered metal receptacles and disposed of daily.
  • Rooms in which flammable or combustible liquids are stored or handled by pumps shall have exit facilities arranged to prevent occupants from being trapped in the event of fire.
  • Inside areas in which Class I liquids are stored or handled shall be heated only by means not constituting a source of ignition, such as steam, hot water or forces central systems located away from the area.

Important to practice good housekeeping and maintain equipment:

Good housekeeping and equipment maintenance are important wherever any chemicals, including flammable and combustible liquids, are used.

  • Keep all areas where these liquids are stored, handled or used clear of burnable materials.
  • Provide drip trays and empty them often wherever recurring leakages occur.
  • Consider using splash guards to enclose machines or processes that eject flammable or combustible liquids.
  • Clean up liquid spills immediately.
  • Remove any obstructions that prevent containers with lids held open by fusible links from closing fully.
  • Make sure that flammable and combustible liquids are not left where they could block or otherwise prevent people from escaping in case of a fire.

Regular equipment inspection and maintenance are important for controlling the hazards of flammable and combustible liquids.

  • Ensure maintenance personnel know the hazards of the materials to which they might be exposed.
  • Carry out repairs to equipment properly, including special equipment like explosion-proof fittings. Fires and explosions have resulted from the addition of non-approved parts or equipment to approved systems.
  • Do not use safety containers that are damaged in any way. If repairs using approved parts cannot restore safety containers to a safe condition, discard the containers once they have been properly cleaned.


Not more than 120 gallons of Class I, Class II, and Class IIIA liquids may be stored in a storage cabinet.

Basic safety practices for flammable and combustible liquids:

Following these basic safe practices will help protect you from the hazards of flammable and combustible liquids:

  • Obtain and read the Material Safety Data Sheets (MSDSs) for all of the materials you work with.
  • Be aware of all of the hazards (fire/explosion, health, chemical reactivity) of the materials you work with.
  • Know which of the materials that you work with are flammable or combustible liquids.
  • Eliminate ignition sources (sparks, smoking, flames, hot surfaces) when working with flammable and combustible liquids.
  • Use the smallest amount of flammable liquid necessary in the work area.
  • Keep storage areas cool and dry.
  • Store flammable and combustible liquids away from incompatible materials (e.g., oxidizers).
  • Use approved containers for disposal of rags and other work.
  • Store, handle and use flammable and combustible liquids in well-ventilated areas.
  • Use approved equipment, including labelled safety containers, for flammable and combustible liquids.
  • Keep containers closed when not in use.
  • Bond and ground metal containers when transferring flammable and combustible liquids.
  • Practice good housekeeping and equipment maintenance. Keep area clear of burnable materials.
  • Wear the proper personal protective equipment for each of the jobs you do.
  • Know how to handle emergencies (fires, spills, personal injury) involving the flammable and combustible liquids you work with.
  • Follow the health and safety rules that apply to your job.



  • Provide proper storage for flammable liquids
  • Ensure proper training is provided to employees who work with flammable liquids
  • Ensure containers are properly labeled


  • Provide adequate training in the use and storage of flammable liquids
  • Monitor for proper use and storage
  • Keep only the minimum amount required on hand
  • Ensure MSDS are current for all flammable liquids


  • Follow all storage and use requirements
  • Report deficiencies in storage and use to supervisors
  • Immediately report spills to supervisors

Hazard Control

Engineering Controls

  • Properly designed flammable storage areas
  • Ventilated Storage areas
  • Grounding Straps on Drums and dispensing points

Administrative Controls

  • Designated storage areas
  • Limiting amount of flammable liquids in use and storage
  • Employee Training
  • Limited & controlled access to bulk storage areas
  • Posted Danger, Warning and Hazard Signs.

Handling flammable materials

Fire prevention

To prevent fires, flammable materials must be properly managed in the workplace. There are three main ways to prevent fires:

(1) Limit the amounts of flammable and combustible materials

  • Keep only what you need on-site.
  • Purchase materials in the smallest volumes necessary.
  • At work locations, keep only those chemicals that are needed for the present task.
  • Do not let hazardous wastes accumulate at the work site.
  • Store products, including wastes, used at the work site in proper containers.
  • Keep flammable materials separate from other processes and storage areas.

(2) Provide proper ventilation to ensure flammable vapours do not accumulate

  • Install properly designed ventilation in storage areas.
  • Ensure that processes that use or make flammable materials do not exhaust back in the work site.
  • Ensure that equipment, such as spray booths, where flammable materials are used, are exhausted outside of the building, and away from air intakes.
  • Ventilation systems must be properly maintained and comply with the Building Code.

(3) Control ignition sources

  • Ground and bond all work and ignition-proof equipment
  • Ensure that there is no smoking in work areas where flammable materials are stored or used
  • Never store flammable materials near hot equipment or open flames
  • Use intrinsically safe and non-sparking tools

It is important that the employer assess the work site and identify potential fire hazards. This will allow the employer to identify the best ways to control these hazards.

Flammable gases

Flammable gases stored in cylinders are usually at very high pressures, so their uncontrolled release can present both physical and flammability hazards. A small amount of the released gas can fill a large area with a potentially explosive concentration very quickly. This is particularly the case with liquefied gases such as Liquefied Petroleum Gas (LPG).

When storing flammable gas in the workplace:

  • store flammable gas cylinders in a separate well ventilated room
  • ensure that cylinders are properly secured so that they cannot fall over and valves are protected from damage
  • always use the correct fittings and valves for the specific cylinder, do not mix and match fittings
  • protect hoses, connections and containers from damage and inspect them regularly for signs of wear.

Static electricity hazard:

Flammable and combustible liquids can present a static electricity hazard depending on their ability to generate static electricity, how well they conduct electricity (conductivity), and their flash point.

Solvents and fuels produced from petroleum (e.g., benzene, toluene, mineral spirits, gasoline, jet fuel) can build up a charge when they are poured or flow through hoses. They tend to hold a charge because they cannot conduct electricity well enough to discharge when in contact with a conducting material, like a metal pipe or container, that is grounded. When enough of a charge is built up, a spark may result. If the vapour concentration of the liquid in air is in the “flammable range” and the spark has enough energy, a fire or explosion can result.

According to the NFPA (Code 77), solvents that are soluble in water (or can dissolve some water themselves) do not build up static electricity. Examples of such liquids include alcohols and ketones like acetone. However, when liquids are transferred into non-conductive containers (e.g., plastic, glass), even conductive solvents may build up a charge because the plastic or glass containers decrease the rate at which the charge in the solvent dissipates.

The flash point and vapour pressure of the liquid and the temperature are other factors to consider. The vapour levels will be higher in the air around the container if you are working outside on a hot summer day than in the winter when the temperature is below 0°C (32°F) or colder.

At higher elevations in the mountains, the air pressure is significantly lower and solvents boil at lower temperatures. Under these conditions, the flash point and the temperature for the optimal vapour/air ratio are lower and some “combustible” liquids can become “flammable”.

A liquid like hexanes has a low flash point and it is flammable when its temperature is in the range -33°C to -3°C (-28°F to +26°F) at sea level. At normal room temperatures, the vapour/air ratio at the surface of the solvent will be well above its upper flammability limit and would be “too rich” to burn. However, at some distance away from the solvent surface, there is a concentration of hexane vapour in the air that is in the flammable range.

A fuel like kerosene is a combustible liquid with a flash point above 38°C (100°F). Under hot weather conditions or if high flash point liquids are heated to temperatures around or above their flash points, a flammable vapour/air mixture will form.

Generally, the conditions for igniting a liquid are optimal when the liquid is used at a temperature that produces a vapour in air concentration (at the surface of the liquid) that is halfway between the upper and lower flammability limits. Recognizing that these conditions represent an “optimal” fire hazard, one has to take appropriate precautions.

Important to bond and ground containers:

Transferring a liquid from one metal container to another may result in static electrical sparks. To prevent the build up of static electricity and prevent sparks from causing a fire, it is important to bond metal dispensing and receiving containers together before pouring. Bonding is done by making an electrical connection from one metal container to the other. This ensures that there will be no difference in electrical potential between the two containers and, therefore, no sparks will be formed.

The best way to bond containers is to securely attach a special metal bonding strap or wire to both containers. Some liquid transfer pumps have self-bonding hoses. Bonding can also be done by keeping a solid metal-to-metal contact between the containers themselves or between a metal container and a conducting nozzle. These latter two methods are usually not reliable because a good electrical contact is often hard to make and maintain during the entire transfer.

In the flammable liquid storage and dispensing area, ground dispensing drums. Grounding is done by connecting the container to an already grounded object that will conduct electricity. This could be a buried metal plate, a metallic underground gas piping system, metal water pipes or a grounded, metal building framework. Bonding both containers and grounding one of them “drains off” static charges and prevents the discharge of sparks. All grounding and bonding connections must be bare metal to bare metal. Remove all dirt, paint, rust or corrosion from points of contact. Specially designed and approved bonding and grounding wire assemblies are available from safety equipment retailers.

Grouding and bonding

Storage Inside Building


Flammable or combustible liquids, including stock for sale, shall not be stored so as to limit use of exits, stairways, or areas normally used for the safe egress of people.

Office Occupies

Storage shall be prohibited except that which is required for maintenance and operation of equipment. Such storage shall be kept in closed metal containers stored in a storage cabinet or in safety cans or in an inside storage room not having a door that opens into that portion of the building used by the public.

General Purpose Public Warehouses

There are tables in the standard summarizing the storage requirements applicable to “General Purpose Public Warehouses.” These tables refer to indoor storage of flammable and combustible liquids which are confined in containers and portable tanks. Storage of incompatible materials that create a fire exposure (e.g., oxidizers, water-reactive chemicals, certain acids and other chemicals) is not permitted.

Warehouses or Storage Buildings

The last type of inside storage covered by this paragraph addresses storage in “warehouses or storage buildings.” These structures are sometimes referred to as outside storage rooms. Practically any quantity of flammable and combustible liquid can be stored in these buildings provided that they are stored in a configuration consistent with the tables in this paragraph.

Containers in piles shall be separated by pallets or dunned where necessary to provide stability and to prevent excessive stress on container walls.

Stored material shall not be piled within 3 feet of beams or girders and shall be at least 3 feet below prinkler deflectors or discharge orifices of water spray, or other fire protection equipment.

Aisles of at least 3 feet in width shall be maintained to access doors, windows or standpipe connections.

Storage Outside Buildings

Requirements covering “storage outside buildings” are summarized in tables in this paragraph. Associated requirements are given for storage adjacent to buildings. Also included are requirements involving controls for diversion of spills away from buildings and security measures for protection against trespassing and tampering. Certain housekeeping requirements are given which relate to control of weeds, debris and accumulation of unnecessary combustibles.

Fire Control

Suitable fire control devices, such as small hose or portable fire extinguishers, shall be available at locations where flammable or combustible liquids are stored.

At least one portable fire extinguisher having a rating of not less than 12-B units shall be located:

  • outside of, but not more than 10 feet from, the door opening into any room used for storage; and
  • not less than 10 feet, nor more than 25 feet, from any Class I or Class II liquid storage area located outside of a storage room but inside a building.

The reason for requiring that portable fire extinguishers be located a distance away from the storage room is that fires involving Class I and Class II flammable liquids are likely to escalate rapidly. If the fire is too close to the storage area, it may be impossible to get to it once the fire has started.

Open flames and smoking shall not be permitted in flammable or combustible liquid storage areas.

Materials which react with water shall not be stored in the same room with flammable or combustible liquids. Many flammable and combustible liquid storage areas are protected by automatic sprinkler or water spray systems and hose lines. Consequently, any storage of water-reactive material in the storage area creates an unreasonable risk.

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Dangerous Reactive Liquids & Solids

Dangerous Reactive liquids & solids

What are dangerously reactive liquids and solids:

Workplace Hazardous Material Information System (WHMIS) 1988 criteria define dangerously reactive liquids and solids as those that can:

  • undergo vigorous polymerization, condensation or decomposition
  • become self-reactive under conditions of shock or increase in pressure or temperature
  • react vigorously with water to release a lethal gas

Vigorous polymerization:

Polymerization is a chemical reaction in which many small molecules (monomers) join together to form a large molecule (polymer). Often the reaction produces heat and pressure. Industry carries out these processes under closely monitored conditions. Other chemicals (catalysts and initiators) and controlled amounts of heat, light and pressure are often involved.

Vigorous polymerization is potentially hazardous because the reaction may get out of control. Once started, the reaction is accelerated by the heat that it produces. The uncontrolled buildup of heat and pressure can cause a fire or an explosion, or can rupture closed containers. Depending on the material, temperature increases,sunlight,ultraviolet (UV)radiation, X-rays or contact with incompatible chemicals can trigger such reactions.

Many pure substances (i.e. uninhibited) can undergo vigorous polymerization quite easily by themselves when they are heated slightly or exposed to light. These include:

  • acrylic acid                                               
  • acrylonitrile
  • cyclopentadiene
  • diketene
  • ethyl acrylate
  • hydrocyanic acid
  • methacrylic acid
  • methyl acrylate
  • vinyl acetate


An inhibitor is a chemical that is added to a material to slow down or prevent an unwanted reaction such as polymerization. Inhibitors are added to many materials that can polymerize easily when they are pure.

Inhibitor levels in materials may gradually decrease during storage even at recommended temperatures. At storage temperatures higher than recommended, inhibitor levels can decrease at a much faster rate. At temperatures lower than recommended, the inhibitors may separate out. This action can result in some part of the material having little or no inhibitor.

Some inhibitors need oxygen to work effectively. Chemical suppliers may recommend checking oxygen and inhibitor levels regularly in stored materials and adding more if levels are too low.

Vapours from inhibited materials do not contain inhibitors. If these vapours condense and form polymers, they can block vents or flame arrestors in process equipment or containers.

Vigorous condensation:

Condensation is a chemical reaction in which two or more molecules join together to form a new substance. Water or some other simple substance may be given off as a by-product. Some polymers, such as nylon, can be formed by condensation reactions.

Vigorous condensation can produce more energy than the surroundings can safely carry away. This could cause a fire or explosion, or rupture closed containers.

Few common pure chemicals undergo vigorous condensation by themselves. Some members of the aldehyde chemical family, including butyraldehyde and acetaldehyde, condense vigorously, but bases or sometimes strong acids must also be present. Some commercial products sold to be mixed for specialized applications may undergo vigorous condensation if they are not stored, handled and used as directed by the chemical supplier.

Vigorous decomposition:

Decomposition is a chemical change in which a molecule breaks down into simpler molecules. Vigorous decomposition is potentially hazardous because large amounts of energy can be released very quickly. This could result in a fire or explosion, or rupture a closed container causing the release of dangerous decomposition products. Some pure materials are so chemically unstable that they vigorously decompose at room temperature by themselves. For example, some organics are relatively safe only when refrigerated or diluted.

Self-reactivity under conditions of shock or increase in temperature or pressure:

Materials in this group are chemically very unstable. Depending on the material, they can react vigorously and, in some cases, explosively under conditions of mechanical shock such as a hammer blow or even slightly elevated temperature or pressure. Materials in this category include:

  • ammonium perchlorate
  • azo and diazo compounds
  • acetylides                                                                                 
  • azides
  • fulminates
  • hydrogen peroxide solutions (91% by weight)
  • many organic peroxides
  • nitro and nitroso compounds
  • nitrate esters
  • perchloric acid solutions (over 72.5% by weight)
  • picric acid
  • picrate salts
  • triazines
  • some epoxy compounds

Vigorous reactivity with water release deadly gas

Some materials can react vigorously with water to rapidly produce gases which are deadly at low airborne concentrations. For example, sodium or potassium phosphide release phosphine gas when they contact water. Alkali metal cyanide salts, such as sodium or potassium cyanide, slowly release deadly hydrogen cyanide gas on contact with water. The cyanide salts of alkaline earth metals such as calcium or barium cyanide react at a faster rate with water to produce hydrogen cyanide gas. This can result in a life-threatening problem in confined spaces or poorly ventilated areas.

Large amounts of corrosive hydrogen chloride gas are rapidly released when water reacts with aluminum chloride, phosphorous trichloride, tin chloride and chlorosilane compounds. When water contacts thionyl chloride or sulphuryl chloride, they decompose rapidly giving off sulphur dioxide gas and hydrogen chloride gas.

Treat all unknown materials as very hazardous until they are positively identified.

Fire and explosion hazards of dangerously reactive chemicals:

Highly reactive chemicals may undergo vigorous, uncontrolled reactions that can cause an explosion or a fire, or rupture sealed reaction vessels or storage containers.

Even slow reactions can be hazardous if they involve large amounts of material or if the heat and gases are confined, such as in a sealed storage drum. Drums that are swollen and distorted from over-pressurization are potentially very dangerous. They may rupture at any time without warning and release their contents.

Some dangerously reactive liquids such as methyl acrylate and acrylonitrile, are also flammable liquids. They give off enough vapour at normal workplace temperatures to form flammable mixtures with air. They can be serious fire hazards at temperatures lower than those at which they would begin to polymerize or decompose.

Fires involving dangerously reactive materials can be more hazardous than normal. The heat from the fire can lead to violent, uncontrolled chemical reactions and potentially explosive ruptures of sealed containers.

Proper ventilation important:

Well designed and maintained ventilation systems remove airborne, dangerously reactive materials from the workplace and reduce their hazards.

The amount and type of ventilation needed depends on such things as the type of job, the kind and amount of materials used, and the size and layout of the work area. An assessment of the specific ways a workplace stores, handles, uses and disposes of its dangerously reactive materials is the best way to find out if existing ventilation controls (and other hazard control methods) are adequate.

Some workplaces may need a complete system of hoods, ducts and fans to provide acceptable ventilation. Others may require a single, well-placed exhaust fan. No special ventilation system may be needed to work with small amounts of dangerously reactive materials which do not give off airborne contaminants.

Make sure ventilation systems for dangerously reactive materials are designed and built so that they do not result in an unintended hazard. Ensure that hoods, ducts, air cleaners and fans are made from materials compatible with the dangerously reactive substance. Systems may require explosion-proof electrical equipment.

Ensure that the system is designed to avoid buildups of dusts or condensation of vapours. The vapours of inhibited liquids are not inhibited. When they condense, the liquid could polymerize or decompose easily.

Keep systems for dangerously reactive materials separate from other systems exhausting incompatible substances. Periodic inspection of ventilation systems will help maintain them in good operating condition.

Containers for dangerously reactive materials:

Inspect all incoming containers before storing to ensure that they are undamaged and properly labelled. Do not accept delivery of defective containers.

Store dangerously reactive materials in containers that the chemical supplier recommends. Normally, these are the same containers in which the material was shipped. Repackaging can be dangerous especially if contaminated or incompatible containers are used. For example, strong hydrogen peroxide solutions can decompose explosively if placed in a container with rusty surfaces. Bottles for light-sensitive materials are often made of dark blue or brown glass to protect the contents from light. Containers for water-sensitive compounds should be waterproof and tightly sealed to prevent moisture in the air from reacting with the material.

Make sure containers are suitably labelled. For materials requiring temperature control, the recommended storage temperature range should be plainly marked on the container. It is also a good practice to mark the date that the container was received and the date it was first opened.

Protect containers against impact or other physical damage that might cause shock. Do not use combustible pallets, such as wood, for storing oxidizing materials or organic peroxides.

Normally keep stored containers tightly closed. This helps to avoid contamination of the material or evaporation of solvents used to dilute substances, such as some organic peroxides, to safer concentrations.

Some dangerously reactive liquids, such as strong hydrogen peroxide solutions or certain organic peroxide products, gradually decompose at room temperature and give off gas. These liquids are shipped in containers with specially vented caps. These vent caps relieve the normal buildup of gas pressure that could rupture an unvented container. Check vent caps regularly to ensure that they are working properly. Keep vented containers in the upright position. NEVER stack vented containers on top of each other.

Storage area for dangerously reactive liquids and solids:

Store dangerously reactive liquids and solids separately away from processing and handling areas and from incompatible materials. Some dangerously reactive materials are incompatible with each other. Do not store these beside each other. Separate storage can minimize personal injury and damage caused by fires, spills or leaks.

Check the reactivity data and storage requirements sections of the MSDS for details about what substances are incompatible with a specific dangerously reactive material.

Construct walls, floors, shelving, and fittings in storage areas from suitable materials. For example, use non-combustible building materials in storage areas for dangerously reactive oxidizers or organic peroxides. Use corrosion-resistant materials for dangerously reactive corrosives.

Ensure that floors in storage areas are watertight and without cracks in which spilled materials can lodge. Contain spills or leaks by storing smaller containers in trays made of compatible materials. For larger containers, such as drums or barrels, provide dikes around storage areas, and sills or ramps at door openings.

Store smaller containers at a convenient height for handling below eye level if possible to reduce the risk of dropping them. Avoid overcrowding in storage areas. Do not store containers in out-of-the-way locations where they could be forgotten.

Store containers away from doors. Although it is convenient to place frequently used materials next to the door, they could cut off the escape route if an emergency occurs.

Store dangerously reactive materials in areas which are:

  • Well ventilated.
  • Supplied with adequate firefighting equipment including sprinklers (sprinklers may not be allowed in areas where materials that react dangerously with water are present).
  • Supplied with suitable spill clean-up equipment and materials.
  • Free of ignition sources such as sparks, flames, burning tobacco or hot surfaces.
  • Accessible at all times.
  • Labelled with suitable warning signs.

Storage temperature important:

Store dangerously reactive materials in dry, cool areas, out of direct sunlight, and away from steam pipes, boilers or other heat sources. Follow the chemical supplier’s recommendations for maximum and minimum temperatures for storage and handling. Higher temperatures can be hazardous since they can start and speed up hazardous chemical reactions. In many cases, inhibitors can be rapidly depleted at higher-than-recommended storage temperatures. Loss of inhibitor can result in dangerous reactions.

Some dangerously reactive materials must be kept at low temperatures in refrigerators or freezers. Use only approved or specially modified units. These are generally known as “laboratory safe”. Standard domestic refrigerators and freezers contain many ignition sources inside the cabinet.

It can also be hazardous to store dangerously reactive materials at less than the recommended temperature. For example, acrylic acid is normally supplied with an inhibitor to prevent polymerization. Acrylic acid freezes at 13?C (55?F). At temperatures less than this, it will partly solidify. The solid part contains little or no inhibitor; the inhibitor remains in the liquid portion. The uninhibited acrylic acid can be safely stored below the freezing point but it may polymerize violently if it is heated to warmer temperatures.

Some organic peroxides are sold dissolved or dispersed in solvents, including water, to make them less shock-sensitive. If these are cooled to below their freezing points, crystals of the pure, very sensitive organic peroxide may be formed.

Alarms that indicate when storage temperatures are higher or lower than required may be needed.

Follow the chemical supplier’s directions about inhibitors used in a particular product. Where appropriate, check inhibitor and oxygen levels and add more as needed according to the supplier’s instructions.

Do not keep a material for longer than the chemical supplier recommends.

Dispensing or using dangerously reactive materials:

Open and dispense containers of dangerously reactive materials in a special room or area outside the storage area. Do not allow any ignition sources in the vicinity. Take care that the dangerously reactive materials do not contact incompatible substances. Use containers and dispensing equipment, such as drum pumps, scoops or spatulas, that the chemical supplier recommends. These items must be made from materials compatible with the chemicals they are used with. Keep them clean to avoid contamination.

When transferring materials from one container to another, avoid spilling material and contaminating your skin or clothing. Spills from open, unstable or breakable containers during material transfer have caused serious accidents.

NEVER transfer liquids by pressurizing their usual shipping containers with air or inert gas. The pressure may damage ordinary drums and barrels. If air is used, it may also create a flammable atmosphere inside containers of flammable or combustible liquids.

Glass containers with screw-cap lids or glass stoppers may not be acceptable for friction-sensitive materials. Avoid using ordinary screw-cap bottles with a cardboard liner in the cap for moisture-sensitive chemicals. Airborne moisture can diffuse slowly but steadily through the liner. NEVER transfer materials stored in a vented container into a tightly-sealed, non-vented container. The buildup of gas pressure could rupture it.

Dispense from only one container at a time. Finish dispensing and labelling one material before starting to dispense another. Dispense the smallest amount possible, preferably only enough for immediate use.

Keep containers closed after dispensing to reduce the risk of contaminating their contents.

NEVER return any unused material, even if it does not seem to be contaminated, to the original container.

If a dangerously reactive material freezes, do not chip or grind it to break up lumps, or heat it to thaw it out. Follow the chemical supplier’s advice.

Avoid dropping, sliding or skidding heavy metal containers such as drums or barrels of friction- or shock-sensitive material.

What are safe techniques to use when handling dangerously reactive materials:

Make sure that all areas where dangerously reactive liquids and solids are used are clean and free of incompatible materials and ignition sources. Do not allow temperatures in these areas to become hot enough to cause a hazardous reaction.


  • Inspect containers for damage or leaks before handling them.
  • Handle containers carefully to avoid damaging them.
  • Keep containers tightly closed except when actually using the material.
  • Avoid returning used chemicals to containers of unused materials.
  • Keep only the smallest amounts possible (never more than one day’s supply) of dangerously reactive materials in the work area.
  • Return unopened containers to the proper storage area at the end of the day and opened containers to a dispensing area at the end of the day.
  • Check that all containers are properly labelled, and handle containers so that the label remains undamaged and easy to read.

Regular workplace inspections can help to spot situations in which dangerously reactive materials are stored, handled or used in potentially hazardous ways.

Basic safe practices when working with dangerously reactive liquids and solids:

Following these basic safe practices will help protect you from the hazards of dangerously reactive liquids and solids:

  • Read the Material Safety Data Sheets (MSDSs) and labels for all of the materials you work with.
  • Know all of the hazards (fire, explosion, health, corrosivity, chemical reactivity) of the materials you work with.
  • Know which of the materials you work with are dangerously reactive.
  • Store dangerously reactive materials in suitable, labelled containers (usually their shipping containers) in a cool, dry area.
  • Store, handle and use dangerously reactive materials in well-ventilated areas and away from incompatible materials.
  • Follow the chemical supplier’s advice on maximum and minimum temperatures for storage and use.
  • Follow the chemical supplier’s advice on checking and maintaining inhibitor and dissolved oxygen levels where appropriate.
  • Eliminate ignition sources (sparks, smoking, flames, hot surfaces) when working with dangerously reactive materials.
  • Handle containers carefully to avoid damaging them or shocking their contents.
  • Keep containers closed when not in use.
  • Keep only the smallest amount possible (not more than one day’s supply) in the work area.
  • Dispense dangerously reactive materials carefully into acceptable containers, using compatible equipment.
  • Do not subject dangerously reactive materials to any type of friction or impact.
  • Be careful when performing operations such as separations or distillations, that concentrate dangerously reactive materials.
  • Practice good housekeeping, personal cleanliness and equipment maintenance.
  • Handle and dispose of dangerously reactive wastes safely.
  • Wear the proper personal protective equipment for each of the jobs you do.
  • Know how to handle emergencies (fires, spills, personal injury) involving the dangerously reactive materials you work with.
  • Follow the health and safety rules that apply to your job.

Good housekeeping important:

Maintain good housekeeping at all times in the workplace:

  • Clean-up any spills promptly and safely according to directions in the MSDS.
  • Use suitable clean-up materials.
  • Properly dispose of unlabelled or contaminated materials.
  • Promptly remove combustible wastes, including wood, paper or rags from work area.
  • Avoid any buildup of chemical dusts on ledges or other surfaces.
  • Ensure that all waste containers used are compatible with the reactive materials, properly marked and located close to the job.

*Note: For example, some commercial sorbent materials used for spill clean-up may initiate polymerization in some monomers. Do not use sawdust or other combustible sweeping compounds to clean up spills of oxidizers or organic peroxides.

Personal cleanliness important:

Personal cleanliness helps protect people working with dangerously reactive materials:

  • Wash hands before eating, drinking, smoking or going to the toilet.
  • Remove contaminated clothing and footwear since they can be a severe fire or health hazard.
  • Wash contaminated clothing and footwear thoroughly before rewearing or discarding. Check the MSDS or contact the chemical supplier for details.
  • Do not wear or carry contaminated items into areas having ignition sources or where smoking is allowed.
  • Store food and tobacco products in uncontaminated areas.
  • Clean yourself thoroughly at the end of the workday.

What should do during emergency:

Act fast in emergencies like chemical leaks, spills and fires:

  • Evacuate the area at once if you are not trained to handle the problem or if it is clearly beyond your control.
  • Alert other people in the area to the emergency.
  • Call the fire department immediately.
  • Report the problem to the people responsible for handling emergencies where you work.
  • Obtain first aid if you have been exposed to harmful chemicals and remove all contaminated clothes.

Only specially trained and properly equipped people should handle the emergency. Nobody else should go near the area until it is declared safe.

Planning, training and practicing for emergencies help people to know what they must do. Prepare a written emergency plan. Update it whenever conditions in the workplace change.

The MSDSs for the materials used are a starting point for drawing up an emergency plan. MSDSs have specific sections on spill clean-up procedures, first aid instructions, and fire and explosion hazards, including suitable fire extinguishing equipment and methods. If the directions in each MSDS section are not clear or seem incomplete, contact the material’s supplier for help.

It is very important to know the best ways to fight fires involving dangerously reactive materials. For example, using water on water-reactive chemicals can cause the rapid release of lethal gas or, in some cases, violent explosions.

There are numerous other sources to turn to for help in developing your emergency plans. The local fire department can provide assistance in this area, as well as training. You can also obtain useful information at little or no cost from environmental and health and safety enforcement agencies, provincial accident prevention associations, St. John Ambulance, insurance companies, occupational health and safety groups, unions, professional associations, certain colleges and universities, and CCOHS. Private consultants who specialize in these matters are also available.

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