Describes how a face velocity monitor was used in a study to indicate average fume hood face velocity on a continuous basis. The monitor consists of a thermal-type sensor mounted on the side wall of the hood and a display unit mounted on the front of the hood. Describes a systematic investigation of the distribution of fume hood face velocity and the factors that influence the accuracy of the face velocity monitor. The study included a four foot bypass hood, a four foot nonbypass hood, a six foot bypass hood and an eight foot combination sash hood. All are commercially available models. Results showed that the centre velocity, the velocity at the centre of the sash opening, adequately represents the average face velocity. Also, with a properly chosen location for the sensor, the air velocity measure by a side wall sensor correlated well with the average face velocity for various sash openings. All face velocities were measured by a thermal-type portable air velocity meter.

KEYWORDS: Sensors, fume cupboards, monitoring, accuracy, air flow.