Basic Hazards

Toxic

Flammable

Reactive

Corrosive

Compressed Gas

Flammable Liquids

Flammable liquids are among the most common of the hazardous materials found in laboratories. They are usually highly volatile (have high vapor pressures at room temperature) and their vapors, mixed with air at the appropriate ratio, can ignite and burn. Flammable solvents have the following properties which describe their hazard potential:
Flash Point
Flammability range
Auto Ignition Temperature

The flash point is the lowest temperature at which a liquid will generate enough vapor to form an ignitable mixture at its surface. Flammable solvents have flash points below 37.8oC (100oF) by definition and many common laboratory solvents (ether, acetone, toluene, acetaldehyde) have flash point well below that. As with all solvents, their vapor pressure increases with temperature and, therefore, as temperatures increase they become more hazardous.

The flammablity range of a flammable solvent represents the range of air/vapor mixtures that can ignite. The flammability range is delineated by the upper and lower flammablity limit. Outside this range of air/vapor mixtures, the mixture will not ignite.

The Auto ignition temperature is the temperature at which a substance will spontaneously combine with oxygen and burn without an external ignition or heat source. Solvents with low auto ignition temperatures have been known to ignite when placed in contact with hot surfaces such as hot plates.

For a fire to occur, three distinct conditions must exist simultaneously: (1) the concentration of the vapor must be between the upper and lower flammable limits of the substance (the right fuel/air mix); (2) an oxidizer, usually the oxygen in air, must be available; and (3) a source of ignition must be present. Removal of any of these three conditions will prevent the start of a fire.

Strategies for preventing ignition of flammable vapors include removing all sources of ignition or maintaining the concentration of flammable vapors below the lower flammability limit by using local exhaust ventilation (such as a hood) or general ventilation. The former strategy is more difficult because of the numerous ignition sources in laboratories. Ignition sources include: open flames, hot surfaces, electrical equipment, and static electricity.

Flammable liquids may form flammable mixtures in either open or closed containers or spaces (such as refrigerators), and will rupture its container if ignited while contained.

The concentrated vapors of flammable liquids are heavier than air and can travel away from a source a considerable distance (across laboratories, into hallways, down elevator shafts or stairways). If the vapors reach a source of ignition a flame can result that may flash back to the source of the vapor.

The danger of fire and explosion presented by flammable liquids can usually be eliminated or minimized by strict observance of safe handling, dispensing, and storing procedures.