Personnel protective equipment is the least preferable option and is discussed in Section 5.0. Engineering methods include both local and general ventilation, and equipment and work area modifications. Ventilation is of special concern as its design and operation are often inadequate. 4.3 Ventilation Evaluation Local ventilation consists of systems designed to remove the toxicant or contaminant from the point of generation, such as a chemical fume hood. General ventilation serves an entire work area supplying and removing air through diffusers or vents strategically located throughout a room.
Many standards exist for proper design, maintenance, and operation of ventilation systems.
The Lab Standard recommends a face velocity of 100 feet per minute at a sash height of 22 inches for chemical fume hoods. Face velocity indicates the speed with which air moves into the hood interior. Hood interiors should be kept free of objects that may impede airflow. Disruption of airflow may reduce the hoods ability to protect personnel. Face velocity is measured with an instrument called an anemometer or thermal anemometer.