Flammable substances are those that readily catch fire and burn in air.  A flammable liquid does not itself burn;  it is the vapors from the liquid that burn.   The rate at which different liquids produce flammable vapors depends on their vapor pressure, which increases with temperature.

The flash point is the lowest temperature, as determined by standard tests, at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid.

Definitions of Flammable and Combustible Liquids:

Class IA
Flashpoint below 73 F (23 C) and boiling point below 100 F (38 C)
Class IB
Flashpoint below 73 F (23 C) and boiling point at or above 100 F (38 C)
Class IC
Flashpoint at or above 73 F (23 C) and below 100 F (38 C)
Class II
Flashpoint at or above 100 F (38 C) and below 140 F (60 C)
Class III
Flashpoint at or above 140 F (60 C)

Acetaldehyde 1A -37.8 21.1
Acetone 1B -17.8 56.7
Benzene 1B -11.1 80.0
Carbon disulfide 1B -30.0 46.1
Cyclohexane 1B -20.0 81.7
Diethyl ether 1A -45.0 35.0
Ethyl alcohol 1B 12.8 78.3
n-Heptane 1B -3.9 98.3
n-Hexane 1B -21.7 68.9
Isopropyl alcohol 1B 11.7 82.8
Methyl alcohol 1B 11.1 64.9
Methyl ethyl ketone 1B -6.1 80.0
Pentane 1A -40.0 36.1
Styrene 1B 32.2 146.1
Toluene 1B 4.4 110.6
p-Xylene 1C 27.2 138.3

Flammable substances (>500ml) should be handled in a laboratory fume hood. (Ventilation is one of the most effective ways to prevent the formation of flammable mixtures especially while transferring a chemical from one container to another or heating a chemical in an open container).

Keep flammable substances away from ignition sources, such as an open flame, static electricity, and hot surfaces.

Heat flammable substances in steam baths, water baths, oil baths, heating mantles, or hot air baths.

When flammable liquids are transferred in metal equipment, minimize generation of static sparks by using bonding and grounding straps as appropriate.

Where feasible (if the quality of the solvent will not be adversely affected) transfer flammable liquids from glass bottles into approved metal safety cans.

Never disable the safety can's spring-load closure.  Always keeps the flame arrestor screen in place.  Replace it if punctured or damaged.

Vacuum work involving flammables must be conducted in a fume hood, glove box or isolated in an acceptable manner.  Evacuated glassware can implode and eject flying glass and splattered chemicals.

Mechanical vacuum pumps must be protected using cold traps and, where appropriate, filtered to prevent particulate release.  The exhaust for the pumps must be vented into an exhaust hood.  Vacuum pumps should be rated for use with flammable liquids.

Flammable chemicals must be stored in flammable liquid storage cabinets that have been approved by Factory Mutual and/or listed by Underwriters Laboratory and designed in accordance with Code No.30 of the NFPA.   (View Flammable Liquid Storage in Section V)

1. Store only compatible materials inside a cabinet.
Do not store paper, cardboard, or other combustible packaging material in a flammable liquid storage cabinet.
Do not overload cabinets;  follow NFPA guidelines for maximum allowable volumes.
2. Flammables should not be stored in areas exposed to direct sunlight.
3. Refrigerators, freezers and other cooling equipment used to store or cool flammable liquids must be "explosion proof" or "laboratory-safe".   Although not considered optimum protection, some domestic refrigerators can be modified to achieve some degree of protection.  Whatever type of refrigerator is used, labeling should be provided that clearly states its intended use.
4. The quantities of flammable chemicals stored in the laboratory should be kept to a minimum.  (View Flammable Liquid Storage in Section V)

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