Lab Safety: Fume Hood Images
Demonstration of Sash Height to Capture Efficiency
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| Hood capture efficiency with sash in full-open position. Note escape of visualization smoke from bottom of hood. |
Note improved capture efficiency with sash in partially-closed position. |
Face Velocity Testing
| The DILHR required face velocity is 100 feet per minute (0.5 m/sec). This velocity is capable of controlling most low-velocity cross drafts and turbulence created by normal working practices at the face of the hood. All hoods should have a sticker designating the maximum safe sash height. Keep the sash at the appropriate level to ensure optimal face velocity.
The smoke visualization test shows this hood is satisfactory. The face velocity at full sash height was 100 feet per minute. |
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ASHRAE 110 Fume Hood Performance Test
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Demonstration of ASHRAE 110 Fume Hood Performance Test.
In this sophisticated test, a tracer gas (sulfur hexaflouride, or SF6) is released at a known rate inside the hood. Samples are taken in the breathing zone of a mannequin standing at different positions in front of the hood. The DILHR mandated pass criteria is 100 parts per billion (ppb) tracer at the breathing zone of the mannequin. UWM experience and other studies indicate there is no good correlation between face velocity of auxiliary air supplied hoods and exposure at the breathing zone using this test protocol. As with conventional style hoods, keep the sash at the appropriate level as indicated by the ASHRAE 110 Method test label to ensure optimal hood performance. This test is performed on the auxiliary air-supplied hoods in the Chemistry Building, iodination hoods, and high-hazard hoods. General purpose hoods are tested using face-velocity and smoke visualization methods. The mannequin is placed 6 inches from the face of the hood. |
| Tracer gas escaping from the hood is measured using an infrared spectrophotometer for near-real time exposure assessment. |  |
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Tracer gas is diffused at 4 lpm using this manifold. Tests are performed for 10 minutes at 3 positions in the hood (left, right, and center). |
| Tracer gas in the mannequin's breathing zone indicates poor hood performance. The test is performed at full-open sash height. |  |
Behind Closed Doors-The Mechanical Systems
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Fume hood mechanical systems, such as this duct, motor/fan unit and stack are checked on a routine basis for proper functioning.
Any suspected malfunctions should be reported to Physical Plant Services for repair. |
Updated May 6, 2008 by SAK