Fume hoods are not just part of the furniture, but are important items of chemical safety equipment with a dynamic mechanical function. A fume hood is the apparatus on which we depend to protect us from exposure to toxic and hazardous chemical vapours, gases and fumes. They are much more than boxes on a duct. They require technical finesse to allow a gentle air flow to provide good fume containment.

Good fume containment depends on the quality of air flow through the fume chamber.

Good air flow begins in the laboratory, by eliminating cross draughts and differential pressure. The average fume hood face velocity, on which we depend for containment of fumes and our protection from harmful fume exposure, is relatively gentle.

Makeup air should enter the laboratory passively and without resistance, allowing the fume hood exhaust system to manage the air flow.

The entry profile of the fume hood should be designed to avoid sudden changes in direction of airflow, which cause turbulence.

A baffle is required across the rear of the fume chamber, to create a diffused and balanced air distribution across the entire work zone. The baffle should cover the entire back wall and part of the roof, and should have multiple openings to ensure complete air balance.

In vertical cross section, the airflow should fan out from the sash opening, up and back through the fume chamber. All air flow pathways should be linear, with as few eddies as possible.

It is not possible to have a single linear air flow with more than one air inlet. Bypass fume hoods typically have high turbulence behind the sash, because two separate air streams from the working opening and the bypass merge together in this zone. While baffles can to some extent control the shape of this turbulence, it is still a zone close to the operator where reverse flow is commonplace. A Variable air volume (VAV) control system allows the fume hood to have a single air inlet, with the air flow regulated in proportion to the size of opening. The mixing zone is eliminated, and air flow conditions inside the fume hood are much improved.

Fume hoods are more expensive that laboratory furniture. This is because they are important items of chemical safety equipment with a dynamic mechanical function. They are subjected to aggressive working conditions with corrosive fumes and liquid spills. Often their housekeeping is neglected. It is therefore important that fume hoods are made to be robust and durable

There are many fume hoods on the market which are mass produced from cheap materials. The materials themselves, and the methods of their assembly, are often unsuitable for an aggressive chemical environment. A good example is a painted metal cabinet resting on top of a bench. Capillary effects draw liquids from chemical spills, splashes, and condensate, into the lap join, with rapid onset of corrosion, which subsequently bursts through the paint finish. Once it starts to look degraded, operators are less likely to keep it clean and tidy, so it gets worse faster. This highlights the importance of making fume hoods with quality methods, and low maintenance synthetic materials.

Steady laminar airflow is at the root of laboratory fume hood safety. It is the means used to control chemical fumes gases and vapours. Therefore it is important to monitor airflow status continuously. Some systems monitor the exhaust fan or the duct, but It is best to measure the true velocity of air entering the fume chamber - face velocity.

There are other hazards present in fume hoods too, especially when electricity and flammable gases or liquids are in use. We need to limit the risk of ignition. Safety sequence control systems manage these risks by disabling ignition sources and energy supplies during start up and shut down phases, and automatically when alarm states occur.