Fume hood

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.

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: In this Fume hood the air is treated and recirculated instead of venting it directly to atmosphere. Fan is mounted on the top of the hood, or below the worktop. Air is drawn through the front opening of the hood and goes through the filter, before passing through the fan and it is recirculated back to the workplace. For a ductless fume hood, filter medium is essential to remove hazardous and noxious substances.Advantage of ductless fume hood, they are mobile, energy saving and easy to install.

Technical specifications

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 hood can be adjusted to the point where capture of contaminants is maximized. Each hood is marked with the optimum sash configuration. The sash should be held in this position when working in the hood and closed completely when 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 the creation of turbulent eddies that can carry vapors out of the hood. The space below the bottom airfoil provides a source 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 area under 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 the airflow 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 evenly across the hood face. Materials such as paper towels drawn into the plenum can create turbulence in this part of the 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 is measured across this plane.