Laboratory fume hoods are designed to shield laboratory users from vulnerable to hazardous materials. Fume hoods provide a secure, enclosed work area for chemical usage and allow acute ventilation for the user and laboratory. Fume hoods should be used when working with or potentially producing a substance that integrates a threshold limit value (TLV) of less than 50 ppm. Fume hoods are typically the most effective method of protection when working with flammables, corrosives, water reactive chemicals, and pyrophoric materials.

Using the concepts of fluid dynamics, Drizgas Tech engineers have designed the Laboratory fume hood to produce horizontal airflow, which reduces the tendencies for turbulence. The innovative and aerodynamic designs of the sash handle, air foil, upper dilution air supply and rear downflow baffle work in concert to produce horizontal airflow patterns that significantly reduce chemical contaminants concentrations throughout the working area.

A laboratory chemical fume hood is a partially enclosed workspace that is exhausted to the outside of the building. When used properly, hazardous gases and vapors generated inside the hood are captured before they enter the breathing zone. This serves to minimize your exposure to airborne contaminants.

Components of fume hood

Hood body	The visible part of the chemical hood that serves to contain hazardous gases and vapors.
Sash	The sliding door of the hood. By using the sash to adjust the front opening, airflow across the hoodcan be adjusted to the point where capture of contaminants is maximized. Each hood is marked with the optimumsash configuration. The sash should be held in this position when working in the hood and closed completelywhen the hood is not in use.
Air foil	It is located along the bottom and side edges the airfoil streamlines airflow into the hood, preventing thecreation of turbulent eddies that can carry vapors out of the hood. The space below the bottom airfoil provides asource of room air for the hood to exhaust when the sash is fully closed. Removing the airfoil can cause turbulence and loss of containment.
Work bench	Generally a laboratory bench top, but also the floor of a floor-mounted hood, this is the areaunder the hood where apparatus is placed for use.
Baffles	Moveable partitions used to create slotted openings along the back of the hood body. Baffles keep theairflow uniform across the hood opening, thus eliminating dead spots and optimizing capture efficiency.
Exhaust plenum	An important engineering feature, the exhaust plenum helps to distribute airflow evenlyacross the hood face. Materials such as paper towels drawn into the plenum can create turbulence in this part ofthe hood, resulting in areas of poor airflow and uneven performance.
Face	The imaginary plane running between the bottom of the sash to the work surface. Hood face velocity ismeasured across this plane.

 

 

DESIGN STYLES OF CHEMICAL HOODS

There are many types of hoods, each with its own design and function. The main type of fume hoods classified based on its function are:

 

Constant Air Volume (CAV) Hoods: With constant volume hoods the volume of airflow into the hood remainsconstant. As the sash is closed the velocity of the airflow entering the hood increases. Properpositioning of the sash is vital to maintaining the optimum face velocity, 80 or 120 feet per minute. Raising thesash too high lowers face velocity, allowing contaminants to escape from the hood. Setting the sash too low willresult in very high face velocities. Face velocities in excess of 120 feet per minute can cause excessive turbulenceand loss of containment.

 

Variable Air Volume (VAV) Hoods: To overcome the drawback of constant air volume fume hood, Drizgas Tech has developed a new version of fume hood based on its function, Variable air volume hoods. The variable air volume hoods are the most sophisticated of the hoodtypes, requiring technically proficient design, installation and maintenance. The primary characteristic of VAVhoods is their ability to maintain a constant face velocity as sash height changes. As the sash is moved the exhaustvolume is adjusted so that the average face velocity is maintained within acceptable parameters. It is bestto use this type of hood with the sash in the half-open position, as this provides more even airflow, and a degreeof face protection in case of an unexpected spill, fire or explosion in the hood. When not in use the sash shouldbe closed to save energy.

 

Different type of fume hoods classified based on application

• General purpose fume hood
• Perchloric acid fume hood
• Walk-in fume hood
• Portable fume hood
• Radio isotope fume hood
• Bench top fume hood
• Double sided fume hood
• Venturi fume hood
• Canopy fume hood
• Inbuilt fume hood scrubber