Vapor pressure and solvent vapor hazards

This paper discusses applications of vapor pressure to industrial hygiene. Vapor pressure is the quantitative term characterizing solvent volatility; it is also equivalent to the concentration of solvent vapor at the liquid surface. The ratio between this concentration at the source and the acceptable concentration at the breathing zone is an intrinsic property of each chemical but varies over 6 orders-of-magnitude among common organic chemicals. The name Vapor Hazard Ratio (VHR) is introduced quantifying this ratio; and its logarithm is termed the Vapor Hazard Index (VHI). Thus, while vapor pressure is directly relatable to the economic effects of solvent evaporation and to airborne concentrations, the VHI has the added component of occupational toxicity. To be used safely and/or acceptably within the workplace, vapors must be diluted from concentrations at the source by a ratio equal to or greater than the Vapor Hazard Ratio, either by general or local exhaust ventilation. It is argued that the VHI can be used currently to predict the relative hazards of vapor concentrations of proposed substitute solvents to be used in similar settings and in hazard communication programs, and in the future with vapor dilution profiles to anticipate achieving quantitative compliance levels with new processes, work practices or ventilation controls. A review of the pertinent vapor pressure literature is also provided.