Flammable Liquids

Flammable substances are the most common hazardous materials found in the laboratory. The propensity to vaporize, ignite, burn or explode varies with the specific type or class of substance. An indicator of the flammability of a solvent is its flash point, the lowest temperature at which a liquid gives off vapor in sufficient concentration to form an ignitable mixture with air. This information is usually available on the label affixed to the chemical container or in MSDS. Flammable liquids are defined as those liquids which have flash points below 100°F (37.7°C). Combustible liquids have flash points between 100°F and 210°F (93.3°C). The most hazardous liquids are those that have flash points at room temperature or lower, particularly if their range of flammability is broad. Flash points and flammability limits of some common chemicals appear in Table .

Table 1: Critical parameters for some common laboratory chemicals. Class IA - Flash point below 730°F, boiling point below 1000°F. Class 1B - Flash point below 730°F, boiling point at or above 1000°F. Class 1C - Flash point at or above 730°F, and below 1000°F.

Flash Point Boiling Point Ignition Temperature Flammable Limit
(percent by volume in air)
Chemical Class (°C) (°C) (°C) Lower Upper
Acetaldehyde 1A -37.8 21.1 175.0 4.0 60.0
Acetone 1B -17.8 56.7 465.0 2.6 12.8
Benzene 1B -11.1 80.0 560.0 1.3 7.1
Carbon disulfide 1B -30.0 46.1 80.0 1.3 50.0
Cyclohexane 1B -20.0 81.7 245.0 1.3 8.0
Diethyl ether 1A -45.0 35.0 160.0 1.9 36.0
Ethyl alcohol 1B 12.8 78.3 365.0 3.3 19.0
n-Heptane IB - 3.9 98.3 215.0 1.05 6.7
n-Hexane 1B -21.7 68.9 225.0 1.1 7.5
Isopropyl alcohol 1B 11.7 82.8 398.9 2.0 12.0
methyl alcohol 1B 11.1 64.9 385.0 6.7 36.0
Methyl ethyl ketone 1B - 6.1 80.0 515.6 1.8 10.0
Pentane 1A -40.0 36.1 260.0 1.5 7.8
Styrene 1B 32.2 146.1 490.0 1.1 6.1
Toluene 1B 4.4 110.6 480.0 1.2 7.1
p-Xylene 1C 27.2 138.3 530.0 1.1


For a fire to occur, three conditions must exist: a concentration of flammable vapor that is within the flammable limits of the substance; an oxidizing atmosphere, such as air; and a source of ignition. Elimination of one of these three will prevent the start of fire or extinguish an existing fire. Air cannot usually be excluded. Therefore, the problem usually involves preventing the coexistence of flammable vapors and an ignition source. Because spillage of a flammable liquid is always a possibility, strict control of ignition sources is important. The vapors of all flammable liquids are heavier than air, and capable of traveling considerable distances. This possibility should be recognized of ignition sources at a lower level than that at which the substance is used.

"NO SMOKING" signs should be posted and obeyed wherever flammable liquids are handled or stored. Never smoke or use an open flame near flammable liquids. Flammables should not be heated with an open flame. Some other type of heat source, such as a steam bath, water bath, or heating mantle should be used. Transfer flammable liquids with caution. The friction of flowing liquids may be sufficient to generate static electricity which in turn may cause a spark and ignition. Therefore, ground or bond all such large containers before pouring from them. (The DESHS can provide the details of this procedure.). Flammable liquids should be dispensed and used in a hood or well-ventilated area so that flammable vapors will not accumulate.

Keep only small quantities of flammable materials available for immediate use. An approved safety can with a self-closing cover, vent, and flame arrester is the best container for storing flammable liquids or waste solvents in small quantities. An ordinary five-gallon container does not provide adequate protection in cases of fire. Refrigerators and cooling equipment used for storing flammable liquids should be explosion-safe (see Section 10).