Helping to clear the air

2nd June 1995 at 01:00
There is nothing like a broken fume cupboard to bring a science lesson to an awkward halt. When this happened to me a few years back the sick cupboard was visited by technician, school keeper, safety officer, Uncle Tom asbestos and all. Every quotation, whether for the repair or stripping out the nasty asbestos or for removing the whole thing made everyone fume.

The portable fume cupboard, or recirculatory fume cupboard, looks like a solution straight out of a box. It is a cabinet where noxious fumes pass over a charcoal-based filter instead of being spewed through a duct out of the building.

More than this, many designs will have all-round acrylic glazing which allows you to, say, work from one side while a class can watch from all angles. You can quickly see what has been wrong with the traditional up-against-the-wall fume cupboard the thing is rarely designed as a place to demonstrate chemicals in action, it's clearly more a place we scientists quietly go to do something rather smelly on our own.

Schools have been known to abandon and seal off their sick fume cupboards and get a more mobile one instead. Portables are now even a serious consideration for new science buildings and laboratory conversions where the cost of running a duct right up through a building will add to the bill of around Pounds 6,000 for the ducted cupboard alone.

On the other hand, portable fume cupboards weigh in at a little over Pounds 2,000, a cost which can be shared by all the laboratories on a floor. You can move them to each room and various extras allow you to connect services such as gas, water and drains though with varying amounts of ease.

But the filters are a continuing and uncertain cost. Their layers of charcoal offer a surface of around 10 square kilometres and adsorb solvent vapours, while other layers such as one of solid caustic soda handle acid fumes.

These will in time become become useless in anything between nought and a few years. There is also a pre-filter, which you change more regularly and sacrifice to prolong the main filter's life. Clearly you need to budget for this, or even squeeze spare filters, each costing over Pounds 200, into the initial order.

Reports from the science consumer organisations CLEAPPS and SSERC (see panel) point to a bigger downside: they say that these filters merely attenuate the fumes. So claims made by manufacturers of "zero emissions" need un-rounding back to a more realistic 0.01 per cent but that is on a good day. What is more, if you were doing advanced work, say producing acidic chlorine fumes, you could easily neutralise the caustic soda part of the filter very quickly. The case for regular monitoring, a burden sometimes taken on by the local authority, cannot be disputed.

However, if you are in the market for a cupboard, it's worth checking equipment bulletins. One of these pointed the finger at models that blow their fumes at the pupils or where a bunsen burned the filter or cracked the glazing when the fan wasn't running. While the cupboards are an option that win on many counts, get third-party advice before buying one off the page.

School subscribers may contact CLEAPPS, The School Science Service, Tel: 01895 251496

Schools in Scotland can contact SSERC, The Scotttish Schools Equipment Research Centre, 24 Bernard Terrace, Edinburgh EH8 9NX. Tel: 0131 668 4421 Philip Harris, Lynn Lane, Shenstone, Lichfield, Staffs WS14 0EE. Tel: 01543 480077

Griffin and George, Bishop Meadow Road, Loughborough, Leicestershire LE11 0RG. Tel: 01509 231166

Astec Environmental Systems, 30-31 Lynx Crescent, Weston Super Mare, Avon, BS24 9BP. Tel: 01934 418685

Bigneat Ltd (Erlab), Solent Road, Havant, Hants, PQ9 1JH. Tel: 01705 492286

McQuilkin BDH Co, 21 Polmadie Road, Glasgow G5 0BB. Tel: 0141 429 7777

Safelab Systems Ltd, 2 Vines Industrial Estate, Nailsea, Bristol, BS19 1BW. Tel: 01275 855131

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