Guidance Document
Flammable and Combustible Liquids

[This is a brief and general summary. Read the full MSDS for more details before handling.]

Introduction: Flammable and combustible liquids present a serious fire hazard because they ignite
easily and burn rapidly. To fully understand this hazard for a specific material requires the knowledge of
such properties as volatility, boiling point, flash point, flammable and/or explosive limits, and
autoignition temperature. These properties are usually available from the material safety data sheet
(MSDS) or other reference material.

In the USA a flammable liquid is one with a flashpoint below 100°F (38°C). A combustible liquid is less
flammable, having a flashpoint between 100°F and 200°F (38 - 76°C). The flammable and combustible
categories are further subdivided based upon flashpoint and boiling point.

Category
Flashpoint
Boiling Point
Examples
Class IA flammable
ethyl ether,
below 73°F
below 100°F
liquids
pentane
equal to or
acetone,
Class IB flammable below 73°F
greater than
benzene,
liquids
100°F
hexane
Class IC flammable equal to or
isopropanol,
liquids
below 100°F
greater than 73°F
MIBK, xylene


Class II
equal to or
combustible
acetic acid,
greater than
below 140°F
liquids
cyclohexane
100°F

Class IIIA
equal to or
naphthalene,
combustible
greater than
below 200°F
phenol
liquids
140°F
Class IIIB
equal to or
ethylene
combustible
greater than
not specified
glycol,
liquids
200°F
glycerine

Flashpoint - The most common property used for classification of flammable and combustible liquids is
flashpoint. The flashpoint is the lowest temperature at which a liquid will give off sufficient vapor to
ignite when a source of ignition is applied. It is the vapor that burns, not the liquid itself.

Flammable/explosive limits - The vapors must be mixed with air in certain proportions in order to
burn. Each flammable or combustible liquid has its own upper and lower flammable/explosive
limits. Concentrations below the lower limit are too lean to burn. Concentrations above the upper limit
are too rich to burn.

Hazards: Fire and explosion are the primary hazards associated with flammable and combustible
liquids. Keep in mind that many of these materials have additional hazards, including toxicity and
carcinogenicity.

Sources of ignition: Flammable and combustible liquids can be ignited by heat, flame, hot object,
electric spark or static electricity. Oxygen by itself does not burn, but it will support or accelerate
combustion of flammable materials. Some materials that are nonflammable under normal conditions
may burn if oxygen is enriched.




Use and Storage Guidelines
1. The main objectives are to avoid accumulation of flammable vapors and to control sources of ignition.
2. Quantities should be limited to the amount necessary for the work in process. Return obsolete
materials to the Chemical Storage and Distribution Facility. Promptly submit all wastes for pickup by
EHS.
3. Whenever possible use flammable and combustible liquids in a fume hood.
4. Flammable and combustible liquids should be stored in a flammable liquid cabinet, an approved cabinet
designed and constructed to protect contents from external fires.
5. Store flammable and combustible liquids away from acids, bases and oxidizers.
6. No more than ten gallons of flammable and combustible liquids, combined, may be stored outside of a
flammable storage cabinet.
7. No container for five gallon capacity or greater may be stored outside of a flammable storage cabinet.
8. All stored containers must be closed and properly labeled.
9. Storage in refrigerator must only be done in an appliance that has been specifically designed and
constructed for flammable liquid storage. Standard household refrigerators must not be
used. Refrigerators must be labeled as to whether they are suitable for flammable liquid storage.
10. Control all ignition sources. The more obvious sources include open flame from Bunsen burner,
matches, smoking, etc. But be aware of less obvious sources including electrical equipment, static
electricity and gas-fired heating devices. Common laboratory equipment is often not intrinsically safe
(stirrers, Variacs, power strips, ovens, heat tape, hot plates, heat guns, etc.).
11. Do not heat flammable liquids with open flame. Use such alternates as steam bath, salt bath, oil bath,
or heating mantle.
12. The pouring of flammable liquids can generate static electricity. Static electricity is more likely to
develop in colder and drier atmospheres. Bonding or use of ground straps can prevent static electricity
buildup. Grounding does not work with non-metallic containers (e.g. plastic bottle or drum). Contact
must be made directly with the liquid.