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Importance of Good Ventilation
Removing Flammable Vapors From Your Workplace

Spontaneous combustion occurs when a material in contact with air can heat up sufficiently (without an outside heat source) to burn.

The oils in some wastes and rubbish can slowly react with oxygen in the air. This reaction creates heat that can build up over time. When the heat level in a “self-heating material” is high enough (i.e., when the temperature reaches the auto ignition temperature), a fire may start.

For example, a rag soaked with vegetable oil in the bottom of a pail could heat up enough to cause spontaneous combustion of the rag. However, the same oil-soaked rag would not be expected to heat up on a clothes line because there would be sufficient contact with moving air that would prevent heat from building up. An oil-soaked rag would not heat up if it were in a tight bale because it would not have enough air.

Why is good ventilation important? Well designed and maintained ventilation systems remove flammable vapors 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 vapors 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 vapors 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 vapors should meet the relevant fire code requirements.

If the ventilation keeps vapor levels below the occupational exposure limit of a chemical, usually there is little risk of fire or explosion. Vapor levels harmful to people are, in most cases, much below the lowest concentration of vapor in air that can burn.

Proper Container Storage

Store flammable and combustible liquids according to the laws, including building, fire, and electrical codes, that apply to your particular workplace. These laws specify the kinds of storage areas, such as storage rooms and cabinets, allowed for these liquids. They also specify how to construct these storage areas and the amounts of flammable and combustible liquids in different types of containers that you can store in each kind of storage area.

There may also be restrictions about the volume (how much) of product that can be stored.

Never use plastic or glass containers for storing flammable liquids unless storage in metal containers would affect the required liquid purity or if the liquid would cause excessive corrosion of the metal container. In all cases, allow only trained, authorized people into storage areas. Before storing, inspect all incoming containers to ensure that they are not damaged and are properly labeled. Do not accept delivery of defective containers.

In general, store containers of flammable and combustible liquids separately, away from process and production areas, and away from other materials. This separation will reduce the spread of any fire to other materials in storage. It will also protect the stored flammable and combustible liquids from exposure to fires in other areas, and accidental contact with incompatible materials.

Keep the amount of materials in storage as small as possible. It is a good practice to keep no more than one day’s supply of flammable and combustible liquids in the immediate work area. Return any leftover material to the proper storeroom or storage cabinet at the end of the day.

What should a good storage area be like?

Store flammable and combustible liquids in areas that are:

• Well ventilated to reduce vapor concentrations. ;

• Free of ignition sources;

• Cool (temperature controlled) and dry;

• Supplied with adequate firefighting and spill clean-up equipment;

• Away from elevators, building and room exits, or main aisles leading to exits;

• Accessible by firefighters; and

• Labeled with suitable warning signs. For example: “No Smoking.”

Avoid storing flammable and combustible liquids in basements. Ground floor storage is usually preferred as it provides easier access for emergency situations. Inspect storage areas regularly for any deficiencies such as damaged or leaking containers, poor ventilation or non-approved equipment. Unapproved modifications or damage to approved or explosion-proof equipment or systems could result in unintended hazardous conditions. Correct all deficiencies as soon as possible.

It may be possible to store small amounts of flammable liquids (less than 235 liters or about 62 U.S. gallons) and combustible liquids (less than 470 liters or about 124 U.S. gallons) in approved containers in specially designed storage cabinets near their point of use.

Volatile, flammable liquids are sometimes stored in refrigerators. Use specially designed and approved refrigerators (generally described as “laboratory safe”) for this. Standard domestic refrigerators contain many ignition sources and should not be used for storing flammable solvents.

Handling Drums Safely

Many workplaces receive flammable liquids in large metal drums or barrels, then fill smaller containers from them. Moving full drums weighing hundreds of pounds by hand can be difficult and hazardous. Specially designed drum cradles are available for moving drums around and can also be used as individual drum storage racks.

Drums of flammable liquids should have pressure- and vacuum-relief venting installed. Normally, this is done as soon as the drum is opened for dispensing. If a stored drum will be exposed to heat sources or large temperature changes, relief venting may be needed.

Storing a full drum in direct sunlight or near other heat sources can increase vapor levels in the drum. This leads to an increase in pressure that could, in extreme cases, cause the drum to rupture. A buildup in pressure can also result in vapor shooting out into the face or onto the clothing of the person opening the drum. A pressure-relief vent prevents this increase in pressure.

Vacuum-relief vents are also useful. If a drum of flammable liquid is subjected to sudden cooling, a partial vacuum can form inside it. This could, in extreme cases, cause the drum to collapse and leak. Also, for proper dispensing of liquids, the space left behind by the liquid in the drum must be replaced with air so that no vacuum forms.

There are different kinds of pressure-relief and vacuum-relief devices, including combination types, available from safety equipment retailers.

Equipment Maintenance

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

• 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; and

• 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. FSM

Source: Canadian Centre for Occupational Safety and Healthy