If the hood fails to meet all of the requisite criteria a label will be affixed to the hood sash indicating that the hood failed, and that it should not be used to provide control of airborne contaminants until it is repaired. A memo will be sent to the Department notifying them that the hood failed, and they are responsible for having it repaired. The hood face is divided into three horizontal rows, one approximately 6 inches from the top, one approximately 6 inches from the bottom, and one approximately in the middle of the sash. Each row is divided into at least six equidistant test locations starting approximately 6 inches from the edges of the hood face. Test locations cannot be separated by more than 12 inches.
Velocity is measured at each of the test locations.
The probe is held at a test location until the reading is stabilized, and then the reading is taken, Individual velocity values are recorded and an average value is determined. A copy of the form is included at the end of this Standard. The average face velocity must be between 80 and 125 feet per minute. C. Flow Visualization 1. The smoke source is moved around the perimeter of the sash opening and around any equipment in the hood, while the flow patterns are observed.