Environmental Health and Safety

MSDS Glossary

The gaseous form of a solid or liquid substance as it evaporates.
Vapor Density
The weight of a vapor or gas compared to the weight of an equal volume of air is an expression of the density of the vapor or gas. Materials lighter than air have vapor densities less than 1.0. Some examples are acetylene, methane, hydrogen. Materials heavier than air, such as propane, hydrogen sulfide, ethane, butane, chlorine, and sulfur dioxide, have vapor densities greater than 1.0. All vapors and gases will mix with air, but the lighter materials will tend to rise and dissipate unless confined. Heavier vapors and gases are likely to concentrate in low places-along or under floors, in sumps, sewers, and manholes, in trenches and ditches where they may create fire or health hazards.
Vapor Pressure
The pressure exerted by a saturated vapor above its own liquid in a closed container. Vapor pressures reported on MSDS are in milliliters of mercury (mmHg) at 68°F (20°C), unless stated overwise. Some important facts to remember are that vapor pressure increases with temperature, and the lower the boiling point of a chemical, the higher its vapor pressure.

Examples of vapor pressures at 20°C in mm Hg:

Acetone 184
Mercury 0.002
Methylene Chloride 350
Phenol 0.36
See General Exhaust, Local Exhaust, and Mechanical Exhaust.
Substance used as sorbent for spill control and cleanup.
The tendency of a fluid to resist internal flow without regard to its density.
A measure of how quickly a substance forms a vapor at ordinary temperatures. Chemicals with higher vapor pressures and lower boiling points will have higher volatilities and will evaporate quicker.

Return to top