Laboratory fume hoods are a type of ventilation system with the primary function is to exhaust chemical fumes, vapors, gasses, dust, mist, laboratory hoods, SS fume hood and aerosol. Fume hoods also serve as
physical barriers between reactions and the laboratory, offering a measure of protection against inhalation exposure, chemical spills, run-away reactions and fires.
A typical fume hood has a box like structure with a movable sash window. Experimental procedures are performed within the hood which is consistently and safely ventilated, usually by means of an extract blower and ductwork. Chemical fumes exhausted and diluted many times over in the atmosphere and has a negligible effect to human health. When environment concerns are of importance, an extract treatment system, often referred to as a scrubber is installed to remove most of the vapors from the exhaust air stream.
The hood functions by maintaining a relatively negative pressure in the interior of the hood to prevent any contaminant from escaping while drawing air in through the hood opening at a consistent rate. A suitable hood face velocity (the speed at which air is drawn into the hood) is of importance to the safe and effective operation of a fume hood. While excessive face velocities can often result in turbulence and reduce containment, insufficient velocities can also compromise hood performance.
In general, a hood’s face velocity is recommended to be between 0.3 m/s (60 fpm) and 0.5 m/s (120 fpm), however it is important to check with local safety regulations on the face velocity recommendation before using the fume hoods.
Bench Mounted Fume Hood
Conventional (Constant Volume):
This is a proven model operated on Constant Volume principle. In this model, majority air enters through the opening of sash. Exhaust volume remains constant. This is very popular and economical model used in general low hazard applications.
Constant Volume by Pass Air:
These types of lab Fume Hoods have the same design as conventional fume hoods but will have slots or louvers on the top front panel. Hence, the air bypasses through the slots as the sash is lowered down or closed. There is a sure intake of air either in closed or open sash position. This redistribution of air prevents high velocity streams inside the hood, which may cause turbulence and compromise chemical fume containment.
Walk-in Type Fume Hood
Walk-in type of Fume Hoods are designed to work with the taller assemblies like 20Ltr, 50Ltr etc. where scientist walks-in to perform bigger assembly applications. The sash in this model is operated horizontally.