Chemistry and Chemical Disasters. Pressure exerted by a saturated vapor above its liquid in a closed container. Important facts to remember: (1) Vapor pressure of a substance at 100ºF will always be higher than the vapor pressure of the substance at 60ºF. (2) Vapor pressures reported on MSDS/s in mmHg are usually very low pressures; 760 mmHg is equivalent to 14.7 psi. (3) The lower the boiling point of a substance, the higher its vapor pressure