Ducted Fume Hoods, or built-in fume hoods, are the most commonly used containment devices within a laboratory, and for this reason often considered as the first option when containing any lab scale operation.
Design Features & Performance Criteria for Ducted Fume Hoods
- The Fume Hood should perform to a recognised standard. In Europe this would be the BSEN14175 or ‘Safecheck’ Containment test and in the USA the ASHRAE 110-1995 test protocol would be the recognised test standard.
- Where vertical sliding sashes are used VAV (Variable Air Volume) control systems must be able to respond effectively to sash movements without adversely affecting overall room turbulence or pressure balance.
- All process piping valve handles should be exterior to hood (outside of sash).
- All power points should be located outside of the fume hood.
- Air flow performance indicators must be provided indicating the airflow condition at the face of the fume hood. The monitor should have an audible and visual alarm to indicate low airflow conditions.
- The average face velocity should be between 0.4 -0.5 m/sec (80 to100 fpm).
- Velocity profile should be uniform across the face of the hood: ±20% of the specified air velocity at all points of hood face when in use.
Positioning of Fume Hoods
Laboratory hoods should not be located:
- Near doorways as movement in and out of the area can affect performance.
- High traffic areas where personnel will be frequently passing the fume hood openings.
- At right angles to each other, as airflow will be affected causing ‘dead spots’ across the face of the hood.
- In remote corners of the laboratory as air turbulence may be a problem.
- Close to or directly under supply air vents unless supply air is dispersed effectively minimizing turbulence.
- Fume hoods should not face each other directly unless separated by a distance of at least 3 meters (10 Feet). Fume hoods positioned closer than this may end up fighting for air and so affect containment performance.