Flammable and combustible liquids are those that exist at room temperature in a liquid form with sufficient vapor pressure to ignite in the presence of an ignition source. Hazards associated with these chemicals are related to their high volatility and they become increasingly hazardous at elevated temperatures due to more rapid vaporization.
Flammable and combustible liquids are classified according to flash points; the minimum temperature at which a sufficient vapor is given off to form an ignitable vapor:air mixture.
Flammable Liquids – flash points below 38 °C (100 °F)
Combustible Liquids – flash points above 38 °C (100 °F)
Flammable/explosive limits represent the range of vapor:air mixtures that will sustain combustion – Lower Explosive Limit (LEL) to Upper Explosive Limit (UEL).
Liquids with broad ranges (e.g. acetylene; LEL = 3%, UEL = 65%) are more dangerous because explosion can occur at almost any vapor:air combination
It is not the liquid itself that burns; it is the vapor from the liquid that burns.
Vapor from flammable/combustible liquids can reach remote ignition sources causing fires
Flammables with vapor densities greater than 1 (heavier than air) can accumulate in sufficient concentrations at floor level to ignite and spread through the room
Acute health effects:
Chronic health effects depend on duration and extent of exposure, but can lead to damage of the lungs, liver, kidneys, heart or CNS. Potential to cause cancer and have reproductive effects. Prolonged exposure can lead to liver or kidney damage.
Liquid solvents have exposure limits (see Table 2 Occupational Exposure Limits for Chemical Substances in the Alberta Occupational Health and Safety Code 2009). In many cases, e.g. chloroform, benzene, dichloromethane, etc., the odor threshold is higher than the exposure limit so if you can smell them you may be overexposed.
Handling and Use (Hazard Control)
The three requirements for a fire (the fire triangle) are fuel, in sufficient concentration to ignite and sustain combustion, an oxidizer or oxygen, and an ignition source. When working with flammable and combustible liquids it is important to control and prevent significant accumulation of vapors and avoid ignition sources. The following precautions should be taken:
Substitute with safer alternatives – higher flashpoints, higher boiling points, etc.
Work in a fume hood – good ventilation is needed to minimize the risk of inhalation and to prevent the formation of flammable or explosive mixtures in air.
Use only in areas free of potential ignition sources (open flames, electrical equipment, static electricity, hot surfaces, etc.). Never heat flammable liquids with an open flame.
Avoid working with flammable liquids and oxidizers in close proximity.
Never transfer, work with, or store flammable liquids in an area where a spill could block an exit in the event of a fire.
Consult compatibility charts to determine the gloves that will provide the best hand protection.
Flammable and combustible liquids must be maintained in approved flammable storage cabinets or safety cans. The amount of flammable and combustible liquid kept in the laboratory should be kept to the minimum necessary for the work being done.
Do not store near oxidizers, corrosives, combustible material, or heat sources.
When necessary to refrigerate flammable or combustible liquids, explosion-proof refrigeration equipment must be used. Regular refrigerators have ignition sources such as the door light switch and thermostat.
In addition to basic laboratory PPE, a fire resistant or, at the very least, a cotton lab coat should be worn. Synthetic and synthetic blend lab coats should be avoided.