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ensure accuracy. Prudent Practices in the Laboratory: Handling
and Disposal of Chemicals molecules to escape from the liquid or
solid phase into the gaseous phase) is the most important
characteristic of a chemical to consider. The higher the vapor
pressure, the greater the potential concentration of the
chemical in the air. For example, acetone (with a vapor pressure
of 180 millimeters of mercury (mmHg) at 20 °C) could reach an
equilibrium concentration in air of 240,000 parts per million
(ppm), or 24%. (This value is approximated by dividing the vapor
pressure of the chemical by the atmospheric pressure—760
mmHg—and multiplying by 1,000,000 to convert to ppm.)
Fortunately, the ventilation present in most laboratories
prevents an equilibrium concentration from developing in the
breathing zone of the laboratory worker. Even very