Fume cupboards are designed to capture and remove hazardous substances generated from practical work carried out within them; toxic gases, fumes, vapours, aerosols or air-borne particulates eliminating any health risks due to exposure.
Fume cupboards function in two ways:
Ducted – where contaminants pass through ducting before being exhausted into the environment.
Recirculating filtered – this type filters contaminated air and recirculates the clean air. Ambient Air is drawn into the hood and mixes with gas, vapours or particulates emitted from the activity within the fume cupboard, it is then drawn through a pre-filter (particle capture) before passing through the Activated Carbon filter and out into the room.
Considerations of the Recirculating Filtered variety:
More cost-effective (lower running costs), easy to install, and relocate if required. Note that these are not suitable if a diverse range of chemicals are used as there is no universal filter but there are many filter types optimised for different applications. They are also not recommended for constant use as this would require excessive filter replacement. Filter life depends on the type, volume, temperature, and duration of chemical usage.
Filter maintenance
It is a Coshh requirement to monitor filters to ensure they are doing their job and haven’t reached saturation but also important to ensure you get the maximum usage from them. This can be done manually, using colorimetric chemical detector tubes and an air sampling pump to determine if chemical breakthrough is occurring, or with an automated Filter Saturation Alarm.
Employing an automated Filter Saturation Alarm that continually monitors for breakthrough is more reassuring as it will alarm immediately once the alarm limit is reached. The manual sampling technique is more laborious and may be implemented too late, i.e. after a break-through has occurred. Another advantage of continuous monitoring is that maximum usage/life is obtained from the carbon filters before replacement.
Airflow
A blower/fan is used to pull air through the hood from the room in which the fume cupboard is situated. Airflow is essential to convey hazardous chemicals/ particulates through the main filter and to prevent their escape through the sash opening out into the room. The minimum face velocity at the opening of the hood should be 0.5 m/s
How can OmniSensors and Transmitters help with your requirements?
OmniSensors and Transmitters is not a supplier of fume cupboards or control systems but we do supply a wide range of gas sensors to the manufacturers. Figaro metal oxide sensors commonly used to monitor filter saturation are the TGS 822 and the TGS 2620.
We also supply E+E Elektronik flow velocity probes and sensors which work on the hot film anemometer principle. The EE 576 is a polycarbonate probe with a voltage output, the EE 680 is a stainless steel probe with analogue or digital output and the EE 660 is a transmitter with analogue or digital outputs and optional display. If you are looking for a mass flow sensor please contact us for more information on the MEMS APSP PFLOW2001-series from Angst and Pfister
For further information on specific sensors or application please contact our friendly sales team
Omni Sensors and Transmitters Ltd.
Tel: 01926 614263
E-mail: sales@sensorsandtrasnmitters.com
Website: www.sensorsndtransmitters.com
