Solvent vapor concentrations following spills in laboratory chemical hoods

Abstract

Chemical hoods are universally recognized as an important engineering control for protecting laboratory workers from chemical exposures. However, recent discussions have renewed questions about possible fire and explosion hazards following spills of flammable liquids inside hoods, and the subsequent potential impacts on laboratory design. In response to similar concerns about systems planned for our institution, we simulated a series of spills with flammable solvents to evaluate the potential for generating explosive atmospheres in laboratory hoods. As part of these tests, we also evaluated the effect of different face velocities and volumetric flows on evaporation rates and flammable vapor concentrations. We found that under the normal range of laboratory room and hood operating conditions, the principal determinant of chemical concentration in exhaust air is vapor pressure, and that volumetric airflow has a significantly greater impact on peak vapor concentration than hood face velocity. Based upon these tests, laboratory-scale spills of common flammable liquids are unlikely to create explosive atmospheres in chemical hood exhaust systems.