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Encyclopedia > Fume hood
A common modern fume hood.
A common modern fume hood.

A fume hood or fume cupboard is a large piece of scientific equipment common to chemistry laboratories designed to limit a person's exposure to hazardous fumes. Fume hoods were originally manufactured from timber, but now epoxy coated mild steel is the main construction material. Two main types of unit exist, ducted and recirculating. With the ducted type, old asbestos vent pipe has been superseded on health grounds, typically with PVC or polypropylene. The principle is the same for all units; air is drawn in from the front of the cabinet by a fan, and expelled either outside the building, or made safe through filtration and fed back into the room. Image File history File links Download high resolution version (1024x768, 111 KB)A fume hood. ... Image File history File links Download high resolution version (1024x768, 111 KB)A fume hood. ... For the scientific journal named Science, see Science (journal). ... Chemistry (from Greek χημεία khemeia[1] meaning alchemy) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms, such as molecules, crystals, and metals. ... Epoxy or polyepoxide is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. The first commercial attempts to prepare resins from epichlorohydrin occurred in 1927 in the United... Plain-carbon steel is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. ... A duct may refer to: An atmospheric duct. ... Fibrous asbestos on muscovite Asbestos Asbestos Asbestos (a misapplication of Latin: asbestos quicklime from Greek : a, not and sbestos, extinguishable) describes any of a group of minerals that can be fibrous, many of which are metamorphic and are hydrous magnesium silicates. ... Polyvinyl chloride Polyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ... Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap Polypropylene or polypropene (PP) is a thermoplastic polymer, used in a wide variety of applications, including food packaging, textiles, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. ... In chemistry, alchemy and water treatment, filtration is the process of using a filter to mechanically separate a mixture. ...

Contents

Construction and location

Fume hoods, fume cupboards are generally available in 5 different widths; 1000 mm, 1200 mm, 1500 mm, 1800 mm and 2000 mm. The depth varies between 700 mm and 900 mm, and the height between 1900 mm and 2400 mm. These can accommodate from one to three operators. They are generally set back against the walls and are often fitted with infills above, to cover up the extract ductwork. Because of their shape they are generally dim inside, so many have internal lights with gas-proof covers. The front is a movable sash, usually in glass, able to move up and down on a counterbalance mechanism. On educational versions, the sides of the unit are often also glass, so that several pupils can gather around a fume hood at once. Alarm control panels are common, see below. An alarm gives an audible or visual warning of a problem or condition. ...


Recirculating Fume Hoods ( Fume Cupboards )

Mainly for educational use, or where the design of a building does not permit the fitting of external ductwork, these units generally have a fan mounted on the top (soffit) of the hood, or beneath the worktop. Air is sucked through the front opening of the hood and through a filter, before passing through the fan and being fed back into the workplace.


Pre-Filtration

The first stage of filtration consists of a physical barrier, typically of open cell foam, which prevents large particles from passing through. A filter of this type is generally inexpensive, and would last for approximately six months, dependent on usage.


Main Filtration

After pre-filtration, the fumes are sucked through a layer of activated charcoal which absorbs the majority of chemicals that pass through it. Ammonia and carbon monoxide will, however, pass through most carbon filters. Additional specific filtration techniques can be added to combat chemicals that would otherwise be pumped back into the room. A main filter will generally last for approximately two years, dependent on usage. Activated carbon (also called activated charcoal) is the more general term which includes material mostly derived from charcoal. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... Carbon monoxide, with the chemical formula CO, is a colourless, odourless and tasteless gas. ...


Pros

  • Ductwork not required.
  • Heated air is not removed from the workplace.
  • Contaminated air is not pumped into the atmosphere.

Cons

  • Filters must be regularly maintained and replaced.
  • Greater risk of chemical exposure than with ducted equivalents.
  • The extract fan is near the operator, so noise may be an issue.

Ducted Fume Hoods ( Fume Cupboards )

Most fume hoods for industrial purposes are ducted. A large variety of ducted fume hoods exist. Air is removed from the workspace and dispersed into the atmosphere.


The fume hood is only one piece of the lab ventilation system. As the recirculation of lab air to the rest of the facility is not permitted, labs operate on single pass air, ie air that is heated or cooled, then used only once prior to discharge.


To reduce lab ventilation costs, variable air volume systems are employed, which reduce the volume of the air exhausted as the fume hood sash is closed. This product is ofte enhanced by the automatic sash positioning system, which closes the fume hood sash when the user leaves the fume hood face. The result is that the hoods are operating at the minimum exhaust volume all of the time that no one is actually working in front of them.


Since a six foot constant volume hood uses as much energy as three average homes in America, the reduction of minimization of exhaust volume is particularly benificial in reducing facility energy costs as well as minimizing the impact on the facility infrastructure. Particular attention must be paid to the discharge location, so as not to risk public safety, or to pull the exhaust air back into the building supply air system.


Pros

  • Fumes are completely eradicated from the workplace.
  • Low maintenance.
  • Quiet operation, due to the extract fan being some distance from the operator.

Cons

  • Unsightly ductwork.
  • Heated air is removed from the workplace.
  • Fumes are dispersed into the atmosphere, rather than being treated.

Specific Fume Hood Types

Low Flow / High Performance

In recent years, laboratory fume hood manufacturers such as LabCrafters (http://www.lab-crafters.com), Fisher-Hamilton (http://www.fisherhamilton.com), Labconco (http://www.labconco.com), and Esco (http://www.escoglobal.com) have developed and introduced energy-efficient low-flow / high-performance fume hoods, designed to maintain or improve operator protection while reducing expensive HVAC operating costs.


Perchloric Acid

These units feature a waterwash system in the ductwork. Because perchloric acid fumes settle, and form explosive crystals, it is vital that the ductwork is cleaned internally with a series of sprays. Perchloric acid has the formula HClO4 and is a colorless liquid soluble in water. ...


Waterwash

These fume hoods have an internal wash system that cleans the interior of the unit, to prevent a build-up of dangerous chemicals.


Scrubber

This type of fume hood absorbs the fumes through a chamber filled with plastic shapes, which are doused with water. The chemicals are washed into a sump, which is often filled with a neutralising liquid. The fumes are then dispersed of in the conventional manner. Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. ...


Use

To determine whether a chemical is likely to require a fume hood for safe usage, its MSDS should be consulted. If there is any doubt, a hood should be used. This page meets Wikipedias criteria for speedy deletion. ...


An operating and maintenance manual should be provided with a new fume hood, which will detail full usage instructions for a new user.


If you already know about the hood you are going to use, begin by making sure no one else is using it or has left things in it. If it's free collect what you need to be in the hood (reagents and/or the experimental apparatus if the products will give off noxious fumes). A reagent or reactant is any substance used in a chemical reaction. ...


If the light in the hood is too dim to see (It probably will be, even if there's enough light in the room you will be working in your own shadow) then turn on the internal light.


Stand (Or sit if there is a stool) where you will be likely to be when you are working, then lower the glass front as far as you can without making it impossible to get your arms under it and work around.


Control Panels

Most fume hoods are fitted with a mains-powered control panel. Typically, they perform one or more of the following functions: Type F Mains power plug & socket The term “mains” usually refers to the general purpose AC electrical power supply (as in “Ive connected the appliance to the mains”). The term is not usually used in the United States and Canada. ...

  • Warn of low air flow.
  • Warn of too large an opening at the front of the unit. Known as a "high sash" alarm, this is caused by the sliding glass at the front of the unit being raised higher than is considered safe, due to the resulting air velocity drop.
  • Provide a method of switching the extract fan on or off.
  • Provide a method of turning the internal light on or off.

Specific extra functions can be added, for example, a switch to turn a waterwash system on or off.


A warning

Even though a properly functioning fume hood provides adequate ventilation, users should not directly smell any chemicals even when using one. Doing this could cause severe damage to the trachea and lungs. A safer method is to wave the palm above the test tube or beaker to waft reduced amounts of the substance towards the user's nose although there is still a danger if toxic fumes are present. Windpipe redirects here. ... The heart and lungs (from an older edition of Grays Anatomy) The lung is an organ belonging to the respiratory system and interfacing to the circulatory system of air-breathing vertebrates. ... A test tube (Sometimes culture tube) is a kind of laboratory glassware, composed of a fingerlike length of glass tubing, open at the top, sometimes with a rounded lip at the top, and a rounded U shaped bottom. ... A beaker is a simple container for liquids, very commonly used in laboratories. ... This page meets Wikipedias criteria for speedy deletion. ... Human nose in profile A typical bulbous human nose Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration. ...


See also

UV light desinfects the sterile laminar flow cabinet when not in use Laminar flow cabinet or laminar flow closet is a carefully enclosed bench designed to prevent contamination of semiconductor wafers, biological samples, or any particle sensitive device. ...

External links

  • University of Louisville's Chemical Hood User's Guide
  • Information from the University of Bath in the UK
Wikimedia Commons has media related to:
Laboratory equipment
Agar plate | Aspirator | Bunsen burner | Calorimeter | Colony counter | Colorimeter | Centrifuge | Fume hood | Magnetic stirrer | Microscope | Microtiter plate | Plate reader | Spectrophotometer | Stir bar | Thermometer | Vortex mixer | Static mixer
Laboratory glassware
Beaker | Boiling tube | Büchner funnel | Burette | Conical measure | Crucible | Cuvette | Laboratory flasks (Erlenmeyer flask, Round-bottom flask, Florence flask, Volumetric flask, Büchner flask, Retort) | Gas syringe | Graduated cylinder | Pipette | Petri dish | Separating funnel | Soxhlet extractor | Test tube | Thistle tube | Watch glass

  Results from FactBites:
 
Chemical Fume Hood (2690 words)
Chemical fume hoods are the primary engineering control used in the laboratory to protect against the inhalation of hazardous vapors and gases.
A fume hood is a partially enclosed workspace that is exhausted, in most cases, to the outside of the building.
Fume hoods are not to be used as a waste disposal mechanism except for very small quantities of volatile materials.
Chemical Fume Hood Handbook (2327 words)
This fume hood, sometimes referred to as a makeup air fume hood, was developed as a variation on the bypass fume hood and reduces the amount of conditioned room air that is consumed.
Fume exhaust duct connections, commonly called snorkels, elephant trunks or flex ducts, are designed to be somewhat mobile allowing the user to place it over the area needing ventilation.
Hoods usually go into alarm mode either because the sash has been raised to a height at which the hood can no longer exhaust a sufficient amount of air, the building air exhaust system is not working properly, or there has been a power outage.
  More results at FactBites »

 
 

COMMENTARY     

KirklandClara28
20th July 2010
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