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Fume Cupboards for Science: Re - circulatory versus extracted to atmosphere

Fume Cupboards for Science: Re - circulatory versus extracted to atmosphere

Sponsored post by S+B UK Ltd

There are two main types of fume cupboard used in the high school environment. The first type is the re-circulatory one (re-circ type) which uses an integral fan and filter system to neutralise chemical fume prior to re-circulating the air back into the science lab. The second type is a traditional fixed fume cupboard (vented to atmosphere type) which uses a duct and fan fume extraction system to draw air from the room, through the fume cupboard, through the system and then discharge to atmosphere outside the building.

The re-circ type

These units are mobile and allow schools with limited budgets to make fuller use of an expensive item through the ability to share a fume cupboard between two or more labs.

This type of fume cupboard can be housed out of the way when not in use and then connected to services located on a teacher’s workstation to allow students to gather around and view a demonstration.

Re-Circ Fume Cupboard
Re-Circ Fume Cupboard

 

Vented to atmosphere type

These are fixed units installed in the most suitable position within the laboratory. Where there is a requirement for a fume cupboard to be used in more than one area, additional fixed units are required.

 

Vented to atmosphere fume cupboard

 

Cost considerations

Re-Circ Vented
  • Initial purchase price
  • Running cost: filter testing, replacement, power consumption for the fan.
  • Initial purchase price: significantly more (double or more) due to the requirement for a fume extraction system.
  • Additional repeated power consumption and replacement air costs for discharging heated/conditioned air to atmosphere

 

Full life cycle and not just initial cost should be considered to determine the true full cost of each option. A well designed and properly maintained fume cupboard should be expected to provide good service for 25 years.

Making a full life cycle cost estimate which compares the two types is not easy and is dependent on usage which will differ from one school to another. When all initial, likely fuel consumption, testing, filter replacement, and maintenance costs are factored into an estimated typical usage, it would seem probable that the re-circ has a significantly lower full life cycle cost by a factor of at least 1 to 2.5 or 3.

Filter testing and replacement for Re-circ type

A re-circ unit will need filter replacement periodically depending on extent of use. The Consortium of Local Education Authority Provision of Science Services (CLEAPSS) and The Association for Science Education (The ASE), which are the two principal independent English schools’ advisory bodies for science, both recommend filter replacement every 4 years for light use units, every 3 years for heavier use teaching labs and every 2 years for chemistry prep rooms. 

Many suppliers will state that a good filter will perform satisfactorily for up to five years although CLEAPSS and The ASE both recommend a filter seal and filter saturation test be carried out as detailed in CLEAPSS Document G9 once every 14 months. These can be carried out by suitably trained school staff as is often the case with mandatory COSHH testing.

Whilst school staffs are mostly comfortable with COSHH testing, there is a tendency to employ a third party to carry out and certify the more complex filter seal and saturation tests.

Fume cupboard filter testing

 

Fume Extraction Systems for Vented type

A fume extraction system involves the purchase of ductwork, a fan and a motor. The fan should be sited on the outside of the building and this may necessitate some builders work to create an orifice in the roof and a weather sealed platform to mount the fan/motor assembly. 

The fume extraction discharge point should terminate above the roof levels of nearby and adjacent buildings (the recommendation is 3m above) in order to prevent fume re-entering the school or into other buildings. The installation process may require a scaffold assembly and it would be necessary to run and connect an electrical supply system from the on/off control in the lab via an electrical distribution board and into the fan on the roof. 

The ductwork should be of a chemically resistant type such as UPVC but it should be noted that this material may not be suited to very hot climates. The alternative would be steel ductwork which can be subject to chemical erosion. The cost of a full discharge to atmosphere extraction system will often be at least the same as the fume cupboard and has the potential for being very considerably more.

Fume Extraction Systems

 

Fuel Consumption, Running Costs and Environmental Considerations

Re-circ Vented
  • Minimal power required to drive the fan. Heated and or conditioned air is recycled back into the room, thus eliminating air replacement costs

  • Uses an activated carbon filter to neutralise chemical fume and re cycles the air, thus minimising environmental impact.

  • The air which is discharged to atmosphere will usually be heated or conditioned at a cost,this has to be replaced at additional cost which is not insignificant. This air replacement cost will be repeated many times over in the lifetime of a fume cupboard
  • Discharges untreated chemical fumes to atmosphere.
  • There are no filter testing or replacement costs required for vented to atmosphere type but COSHH testing and general maintenance is still required
  • Ductwork and fans will need periodic maintenance work and may even need full replacement in the lifetime of a fume cupboard due to weather conditions or damage caused by birds
     

 

Fuel Consumption, Running Costs and Environmental Considerations

 

Limitations of use

Re-circ Vented
  • There is no such thing as a universal filter which can deal effectively with every chemical. Filters are developed for school use which satisfy most requirements, but which do have some restrictions of use
  • Document G9 provides an excellent list of what can and can’t be used in re-circ fume cupboards as well as information on testing protocols, maintenance and operator behaviour.
  • Extracting all fumes through a ductwork system and discharging to atmosphere means there are fewer restrictions of use than is the case with re-circ type units.
  • Building type, location and proximity with other buildings will mean that running external ductwork and fans is prohibited in some circumstances.

 

Operator safety

Re-circ Vented
  • Filters do need testing and replacement periodically to minimise potential for hazardous fumes to re circulate around the school lab.
  • Removing fumes entirely from the room eliminates the problems associated with a failure to replace filters when needed
  • Fewer restrictions of use and discharging fumes to atmosphere make operator exposure to fumes less likely.

 

Flexibility, full costs and environmental issues are all important considerations, but it should be remembered that the primary function of a fume cupboard is to optimise protection for students, teachers and lab technicians from exposure to harmful and irritating fumes.

 A fume cupboard is first and foremost a piece of safety equipment. It is very important to remember that a fume cupboard of any type is not a total containment cabinet and should never be treated as such. All fume cupboards however well designed can and will leak fumes in certain conditions for example where there are excessive cross drafts, badly sited air input grills, heavy traffic passing the unit and operator indiscipline. For this reason, there tends to be a higher prevalence of chemical smells in school science laboratories where there are multiple fume cupboards in one area being used on a regular basis.

Conclusion

There is a case for both types of fume cupboards. A fume cupboard of any type is better than no fume cupboard at all. There is developing trend to balance the considerations and use what is most appropriate in the given circumstances. That can mean using a combination of both types i.e. using vented to atmosphere where needed and where possible for areas like prep rooms and heavily used 6th Form Chemistry Labs and sharing re-circ type in smaller numbers for lighter use general laboratories. 

Choosing a type and supplier

A professional specialist manufacturer should always be able to give best advice. Those that are comfortable offering both options are most likely to recommend the best option in the given circumstances. 

Always check out references, check for independent verification of compliance with relevant standards, check out full extent of supply (to avoid skewed presentation and advice) try to visit completed installations as a minimum and wherever possible and better still, visit prospective suppliers manufacturing facilities. This process can be very revealing and worthwhile in assisting an important capital expenditure decision for a 25-year investment, which has significant health and safety implications.
 

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Mike Serridge is Managing Director at S+B UK, one of the UK’s longest established and leading specialists in the design, manufacture and installation of laboratory furniture, fume cupboards and associated services. S+B have been awarded The Queens Award for Enterprise, International Trade. This was awarded for the extensive advice, consultancy, design, manufacture and installation of laboratory furniture and fume cupboards for International Schools worldwide. This award is the UK’s highest accolade for business success with winners selected by the Prime Minister’s office and approved by Her Majesty the Queen. If you would like more information on fume cupboards and other furniture systems provided by S+B please visit www.splusb.co.uk or contact Mike at mike_serridge@splusb.co.uk. Alternatively, check out their Twitter, Facebook and Youtube pages.

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