Absolute Carbon Filters Ltd. has published guidance to help ensure fume cupboards are kept safe and well-maintained.
A ductless (also known as recirculating) fume cupboard is an enclosure usually manufactured from stainless steel and acrylic or glass which uses an internal fan to move air through one or more carbon filter(s) to absorb chemical fumes and protect the wider environment as well as the user from harmful gases.
The number of carbon filters required in a fume cupboard depends on the size of the unit and the variations of chemicals in use. For complex work with multiple chemicals used in high quantities, a ducted fume cupboard which extracts air to the atmosphere at a safe location (usually the roof of the facility), would be advisable.
One of the most commonly asked questions is how to know when carbon filters need replacing. Fume cupboard specialist engineer, Chris Downey, of Crowthorne Group offers some advice:
There are three ways to test if a carbon filter needs to be changed:
1. A Carbon Breakthrough Test is a definitive way of telling if a carbon filter needs to be changed. An engineer will use 100mm of Isopropanol, poured into a beaker and placed on a heating panel within the work area of the fume cupboard. As the chemical is ‘burnt off’ within the cabinet, the GASTEC Gas Detector Tube System is used above the filter to test exhausted air for fumes. Exhausted air is pulled through a GASTEC tube using their specially designed pump. If escaping fumes are detected the inside of the tube changes colour indicating the filter is no longer adequately absorbing fumes and so is due to be changed.
Find out more about how the GASTEC system works here:
2. Indicator or Sniffer Test offers a strong indication as to whether the carbon filter needs to be changed. Alcohol is sprayed into the work area of the fume cupboard and a sniffer machine is used to detect any alcohol being expelled via the carbon filter into the environment. Alcohol is absorbed by any type of carbon filter (except Mercury filters), so is the chemical of choice when testing carbon filters in ductless fume cupboards.
3. If customers want to test if a carbon filter needs changing for themselves, they can use a simple airflow test by holding an anemometer against the front aperture of the cabinet. The anemometer reading should be close to the reading of the last service or exactly as shown on the display on the cabinet. A reduced airflow reading would indicate that the filter is becoming saturated and so air is passing more slowly into the fume cupboard and through the filter. If this happens, an engineer should be called out to validate the airflow test with the Carbon Breakthrough Test or Sniffer Test and replace the pre-filter and/or carbon filter as necessary.
Another question commonly received at Absolute Carbon Filters is ‘When should I call an engineer?’ There are four main, equally important, reasons.
1. A fume cupboard should not go 12 months without a service visit.
2. If there is the smell of chemicals in the laboratory! This is a simple indicator that there is something wrong and an engineer should be called.
3. If the fume cupboard is sounding an alarm or otherwise indicating a warning, this would indicate there is an issue with the internal workings or airflow. An engineer will be able to diagnose the issue and advise a solution if a fix cannot be made during the initial visit.
4. If there is an obvious physical fault such as broken sash, hole in the filter etc., an engineer should be called.
Absolute Carbon Filters Ltd.’s service partner, Crowthorne Group (www.chts.co.uk), can discuss any queries regarding the operation of your fume cupboard and book an engineer visit as necessary.
By far the most common question received by the company is ‘How long will my filter last?’. The longevity of filters will depend on the frequency of use and the test process carried out. It is advised that carbon filters are changed at least every two years as an absolute minimum.
Find the answers to these questions and more at: https://absolutecarbonfilters.co.uk/faq