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FUME CUPBOARDS

Fume Cupboards fumecupboard

Fume cupboards are designed to prevent exposure to harmful chemicals but the ability of a fume cupboard to prevent exposure depends on a number of factors.

These include:

  • Choosing the most appropriate type of fume cupboard
  • Correct siting of a fume cupboard in relation to other air handling systems, walkways, doors and other air flows within a room
  • Correct use of the equipment
  • Regular maintenance and testing

 

Fume cupboards generally fall into two categories – ducted and re-circulating:

Ducted fume cupboards are the most commonly found type and suitable for most work with chemicals, including radioactive materials (subject to risk assessment). Ducted fume cupboards have an exhaust ducted to the outside atmosphere, usually via a stack / chimney with a height above roof level designed to ensure full dispersion of contaminated air away from areas where people might be affected.

Re-circulating fume cupboards are less common but can be used for lower risk laboratory work – i.e. if working with non-toxic, non-corrosive or non-flammable substances, or if working with very small quantities of hazardous substances. Unlike ducted fume cupboards, re-circulating models pass air through a filter housing before venting it back into the room. The filter plays a crucial role and therefore special considerations must be made:

  • Selecting the correct type of filter
  • Timely replacement and disposal of filters using a safe method – make sure you know the life span of the filter and ensure an expiry date is indicated
  • Limiting the volume of chemicals used at any one moment.

Fume cupboards are not suitable for use in the following scenarios:

  • Working with micro-organisms or other biological agents (microbiological safety cabinets must be used)
  • Handling nanoparticles / nanotubes
  • Using large quantities of incompatible materials which could mix in extract ducting
  • Handling radioactive substances -if the fume cupboard is recirculating
  • Regular handling of toxic and/or flammable solvents in large quantities
  • Using hydrofluoric, perchloric or hot concentrated mineral acids – in these cases, a more specialised type of fume cupboard may be required
  • If a laboratory is not ventilated by other means

In all cases, a risk assessment should be completed to determine if the type of LEV is suitable for the substances in use.

Face velocity
The optimal average face velocity (extraction rate) for LEV varies depending on the type of fume cupboardand the substances in use. Below is an indication of potimum velocities with a 50cm sah opening:

  • 0.35 m/s for low velocity fume cupboards and work not involving very toxic substances (unless in minute quantities)
  • 0.625 m/s for normal velocity (older model) fume cupboards
  • 0.75 m/s for work involving radioactive substances, regardless of fume cupboard model

Note that the face velocity should be no more than 1 m/s at the working opening; otherwise loss of containment is likely to result due to turbulence.”

Siting of fume cupboards within a laboratory

 

 

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