All you need to know about fume cupboard commissioning, containment and LEV testing
PURPOSE AND LIMITATIONS OF FUME CUPBOARDS
Fume cupboards are designed to prevent exposure to harmful chemicals. They are not designed for use with micro-organisms. Microbiological safety cabinets must be used for this purpose.
The containment or ability of the fume cupboard to prevent exposure of the operator to harmful substances depends on a number of factors. These include the following:
- The initial design and meeting of minimum standards (e.g. BS 7258 and BS 7989),
- Subsequent maintenance and testing of the installations,
- Siting of fume cupboards in relation to other extract equipment, pedestrian traffic and local air flows within the laboratory,
- The amount of storage of equipment and chemicals
The types of activities carried out within the fume cupboard and for recirculating fume cupboards:
- The selection of the correct type of filter,
- The timely replacement of filters using a safe method,
- Safe disposal of filter,
- The volume of chemical challenge presented at any one moment
Testing can be carried out for fume cupboards with ducted / centralised extract fans or self-contained recirculating systems, with appropriate filtration systems. The same testing criteria is also used for ventilated benches.
Fume Cupboard testing is carried out to BS 7258, either full or reduced accuracy pt 1 annex D (maintenance /14 monthly testing). British Standard BS 7989 (3) contains similar advice for recirculating fume cupboards. This includes:
- Review of hazardous substances/groups being used,
- If self contained review of appropriate filtration and standards; pre and HEPA filters, carbon filters, water / gas scrubber systems etc.
- A full report for each LEV system will be provided, including:
- Diagram of system and ducting.
- Face velocity readings, together with matrix and performance data
- Check of worktop seals
- Inspection of sash mechanism for corrosion and damage
- Inspection fans, motors, drives and bearings for vibration / overheating etc.
- Check correct fan belt tension, alignment and condition
- Inspection of spray/water wash/scrubber system in fume cupboard etc. if fitted
- Check condition and operation of controls and alarms
- Check function of sash stop
- Check fire damper and release mechanism
- Check fan impellers for wear and corrosion
- Check condition of flexible connections
- Check stability and condition of discharge stack
- Inspect condition of extract ducting and joints
- Check need for cleaning inside ductwork through access ports if fitted
- Recommendations and comments
DfEE Fume Cupboards; Bulletin 88
Operation in Schools, will be used for compliance / testing guidance in schools / colleges.
BS 7258 (1994) Parts 1-3 inclusive. The containment value of the fume cupboards as described in Part 4 of the British Standard shall have a mean value of <0.005ppm and a maximum value of <0.010ppm.
EN 14175 (2003) Part 3. The containment value of the fume cupboards as described in the Standard shall have a mean value of <0.005ppm for both the Inner and Outer Plane Containment Tests and a value of 0.028ppm for the Robustness of Containment Test. Tests carried out with an average face velocity of 0.4m/sec.
ANSI/ASHRAE 110 (2005). The containment value of the fume cupboards as described in the Standard shall have a mean value of <0.005ppm.
Definitions
Average Face Velocity means the inward airflow velocity measured in several specific locations across the plane of the fume cupboard sash opening. Air velocities measured in any single location should not vary by more than 20% from the mean. (Note for most work the average should be equal or greater than 0.5m/s (metres per second) at an opening of 500mm).
Compensating Fume Cupboards
These types of fume cupboards achieve more stable flow velocities at different sash openings by allowing air to enter from a bypass system as the sash is lowered or raised.
Containment This is a measure of how well the fume cupboard is able to prevent escape of any substance released inside the enclosure.
Fume cupboards should have a better containment then 105, which means that one particle may escape for every 100,000 released within the fume cupboard. Containment is affected by average face velocity, design of structure, external air currents and equipment inside the fume cupboard.
Hazardous Substance Have been classified by the CHIP Regulations (4) into the following types:
- Very Toxic Sensitising agent
- Toxic Carcinogenic
- Harmful Toxic to reproduction
- Corrosive Mutagenic
- Irritant
- Biological agents (micro-organisms, blood and body fluids etc) are also covered by this classification, however, these substances should not be used in a fume cupboard.
Make-up Air
This is the air supplied to the room to replace that removed by the fume cupboard. This must not rely on windows and doors having to be opened.
Safe Point
Sash position at which the average face velocity is equal or greater than 0.5m/s. this is normally used where average velocity is below 0.5m/s at a sash opening of 500mm.
Working Opening
Is the height up to which the sash may be raised whilst the experimental procedure is being carried out to ensure a velocity of no less than 0.5m/s. (For experiments involving low risk an average face velocity of 0.3m/s to 0.5m/s would be acceptable). The working height of the sash in vented fume cupboards should not normally be above 500 mm.
Please contact us if you require fume cupboard design, installation, commissioning, testing or maintenance services.