Fume hood
A fume hood (or fumehood), also known as fume cupboard is a type of local ventilation device that is designed to limit exposure to hazardous or toxic fumes, vapors or dusts. Fume hoods are vital in the operation of most chemistry labs.
Design
Fume hoods consist of a cabinet like enclosing, where the back panel is an opaque solid material either straight or oblique, the bottom panel is also solid and flat, the two lateral sides can be either opaque solid material or sliding glass doors, while the top part contains the exhaust vent. The bottom panel is set at standing work height. Under the work stand, there is usually a cabinet where chemicals are kept. At the far end of the work stand, there are at least two water sinks. The lower half of the back panel contains water taps, or sometimes compressed air, inert gas, vacuum, etc. They are controlled by valves set outside the fume hood. The front panes is the most important part of the fume hood. It consists of a sash window, usually made of tempered or laminated glass. It can be moved up and down on a counterbalance mechanism.
Two main types of fume hoods exist: ducted, where the air is evacuated from the room and recirculating (ductless), where the air is evacuated, filtered and sent back in the lab.
Fume hoods are lined with various chemical resistant materials, such as fiberglass reinforced polyester (FRP), epoxy resins, phenolic resins, stainless steel.
Fume hoods in general should not have any inner corners or hard to reach places, as these places allow dust, dirt and easily condensable compounds/fluids to build-up and may not be cleaned properly.
For handling dangerous compounds such as perchloric acid, the fume hoods must have a special washing system, to prevent the build-up of explosive salts or compounds. Likewise, PTFE coating is used for fume hoods where work with hydrofluoric acid or fluorine interhalogens is being done.
Uses
Fume hoods are virtually indispensable in chemistry, as they provide an adequate environment where chemical reactions can be safely performed, as well as a good safety location for various hazardous processes or reagents.
Safety
Fume hoods prevent the build-up of explosive gasses, and can be used as a ventilation device for removing persistent smells from the lab.
Maintenance
Fume hoods are vital equipment in removing various gasses and particulates from the lab, and periodic maintenance is required. The air pump needs to be checked for any signs of corrosion. Likewise, the "roof" and the walls of the fume hood may be corroded if used for long periods of time.
If there is a water source, always check the tap and the sink, for any leaks.
Do not let any volatile compounds inside a fume hood unsupervised for any periods of time, especially if the ventilation is on.
If one works with potentially explosive vapors, such as hydrazoic acid, perchloric acid, certain peroxides, etc., special washing systems are required to remove the build-up of their explosive precipitates. Since these washing systems are vital, they must be periodically emptied and checked for any spills. Such fume hoods should NOT have any recesses, as such places are difficult to clean and the build-up of dangerous compounds in them may compromise the safety of the fume hood.
