Backdraft

Back-Draft exhaust hoods and systems can be an essential component of a Local Exhaust and Ventilation system.

Key Design Criteria: 

Capture velocity: When designed with capture velocity in mind, Back-Draft hoods are an excellent 'No-Fuss' way of removing respirable hazards and improving air quality in your facility. All aerosols have a speed at which they can be drawn into a hood. You must be able to capture it if you are going to control it.

Face Velocity: Understanding the appropriate face velocity is not only essential for the proper capture of airborne pollutants, but it will also determine the noise generated at the hood. It is common to see poorly designed LEV systems with unacceptable noise levels.

Transport Velocity: Evaluating your hood's transport velocity will help you understand whether you will have the contaminant fall out of the airstream and stay in your hood. This could lead to a falling hazard or, perhaps worse, a fire hazard.

Conclusion:

If you take the time and follow these and other relevant design criteria & recommendations such as ASHRAE, SMACNA, ACGIH, you will be well on your way to a successful ventilation solution.