Laboratories
Fume hoods: what to plan before you buy
Published 6 min read
A fume cupboard protects the people in the lab from vapours, dust and aerosols. It only works if the right type is chosen, sited well and connected to services that can support it.
This guide covers the main types, how they are tested, and the questions to settle before you order.
How a ducted hood works
- 1Room air is drawn in through the sash opening
- 2The baffle spreads the airflow evenly across the work area
- 3Vapours are carried up into the exhaust duct
- 4The duct exhausts outside the building
The main types
| Type | How it works | Suits |
|---|---|---|
| Ducted | Draws air in at the front and exhausts it outside the building | Most hazardous chemistry, especially volatile or high-volume work |
| Recirculating (ductless) | Filters the air and returns it to the room | Where ductwork is impractical and the filter suits the specific contaminants |
| Variable air volume (VAV) | Reduces extract as the sash closes to save energy | Labs with many hoods and a controlled supply system |
| High-heat and acid-duty | Built for heat and aggressive acid loads | Perchloric acid and similar work, usually ducted with wash-down surfaces |
Typical values for guidance. Final specification is confirmed per project.
How hoods are tested
Ducted fume cupboards are tested under the EN 14175 series. Part 3 covers type testing of safety and performance, including face velocity and containment. Part 4 covers on-site testing, with commissioning checks on face velocity, extract volume flow, containment and alarms. VAV hoods add Part 6, high-heat and acid hoods Part 7, and recirculating filtration hoods are tested separately under EN 17242.
Face velocity, the speed of air through the opening, is a key figure. A typical value quoted for hazardous work is around 0.5 m/s, but the requirement comes from the standard and your local rules, so confirm it with your safety officer.
Plan these before you order
Exhaust and make-up air
A ducted hood needs building exhaust capacity and replacement air. Agree this with the services contractor early.
Siting
Away from doors, busy walkways and supply diffusers that disturb airflow at the opening.
Chemicals used
The work decides the type, the worktop and the liner. Strong acids and high heat need special-duty construction.
Services and finish
Taps, gas and power drops, a compatible worktop and the finishes around the hood.
Commissioning
Plan the on-site tests and who signs them off before handover.
Frequently asked questions
Ducted or recirculating?
Ducted is the usual choice for hazardous chemistry. Recirculating suits specific, filter-compatible uses where ducting is impractical. Match the choice to the chemicals and get supplier confirmation.
Do you supply the extraction fan and ducting?
Ducting and fans are normally part of the building services scope. We coordinate the interface and install the hood, service drops and surrounding finishes.
How often are hoods tested?
On commissioning and then routinely, as set by your safety rules and the standard. Keep the test records with the lab’s documentation.
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