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Preventing Chemical Accidents:  Understanding MSDS’s & Assessing Chemical Hazards

Factsheet #11 continued

Chemical Properties

Boiling

Point

The boiling point of a substance is the temperature at which the liquid boils or becomes a gas. The lower the boiling point, the quicker it evaporates and the easier it is to inhale. Chemicals with boiling points below 100ºC (or 212ºF) require special caution.

Vapor

Pressure

A high vapor pressure indicates that a liquid will evaporate easily. Chemicals which evaporate quickly are called volatile. This means that air concentrations can build up quickly, even though the substance is in liquid form. Liquids with high vapor pressures may be especially hazardous if you are working with them in a confined space or an enclosed area.

Vapor

Density

If the vapor density is less than one, it will tend to rise in air.  If the vapor density is greater than one, it will fall in air and concentrate in the bottom of tanks or confined spaces.

Appearance and Odor

This information may help identify a substance that spills or leaks in your work area. However, many chemicals are hazardous at levels lower than they can be smelled. Also, many chemicals, such as hydrogen sulfide and ammonia, cause “olfactory fatigue”, which means that workers rapidly lose their ability to smell the substance.

Specific

Gravity

If the specific gravity is greater than one, the substance will sink in water; if less than one, it will float on top of water.

Evaporation

Rate

This is the rate at which a substance evaporates compared to either ether, which evaporates quickly, or butyl acetate, which evaporates slowly. If the substance has an evaporation rate greater than one, it evaporates faster than the comparison substance.  For comparison to butyl acetate, fast evaporation is 3.0 and above, slow is 0.8 and below, medium is anything in between.

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