For this reason, the term equilibrium vapor pressure is sometimes used. Vapor pressure and boiling point have an intimate relationship. The boiling point is the temperature at which the vapor pressure of the liquid equals the external pressure. For example, because the air pressure is lower in a city far above sea level such as Denver, the boiling point of water is lower than in a sea level city such as New York. The most common unit for vapor pressure is the torr .
Most materials have very low vapor pressures.
For example, water has a vapor pressure of approximately 15 torr at room temperature. In general, the higher the vapor pressure of a material at a given temperature, the lower the boiling point. MSDS Relevance Depending on its vapor pressure, a volatile substance can easily form a significant concentration of vapor, especially in an enclosed space. If that vapor is flammable , a fire or explosion could result. This vapor pressure does not need to be large.