Rank: New forum user 
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I'm being asked to test fume cupboards with apparatus still in them; I am told that it is too disruptive to remove all the contents for testing.
Whilst in most cases we are able to confirm an average face velocity above the 0.5m/s design velocity (using 3 readings at each of approx 12 positions across the face). The positiontional readings can vary between 0.32m/s and 0.9m/s depending where apparatus in the cupboard are relative to the test position. My understanding is that minimum velocity should be greater than 80% of design velocity ie 0.4m/s but I can't see how this can be accurately measured with cupboards full.
Does anyone else have this issue? If so what criteria have you used to confirm that fume cupboard is performing adequately?
Thank you for any advice or pointers you are able to give.
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Rank: Forum user
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No great guidance to offer, other than a knowledge of aerodynamics.
Obviously any obstructions in a flow stream will cause turbulence and back flow within the flow fluid.
So I would agree, I don't see how you can get reliable results, as you have described with obstructions in the fume cupboad.
Within pipe lines etc, where flow meters are installed - the sensor is ideally installed (depends on type etc 5-10 pipe diameters downstream/away from pipe bends, valves etc - so that the fluid flow is settled and has little turbulence.
I would insist the fume cupboards are cleared out before testing, but at the end of the day if the operators ae going to use the fume cupboard and obsruct the air flow because of equipment in the fume cupboard, it does suggest at the very least poor practice.
What is the fume that is being extracted / hazardous material - how hazardous is it? Toxic, flammable, iritant etc?
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Rank: Super forum user 
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Two things occur to me as a layman in this matter:
1. What standard are you using to measure the test against and what does it have to say about obstructions in the cupboard?
2. The stuff in the cupboard is real-life usage, so the flows that you are measuring represent the reality of the extraction system's ability to remove hazardous substances.
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Rank: Super forum user
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As per BS EN 14175-4:2004, clause 5.4 is about Face velocity test for onsite testing of Fume-Cupboards
5.4.3 Test procedure and test results
The fume cupboard shall work with the intended working conditions. No other equipment than the test equipment shall be present inside the fume cupboard. The measurements and the calculation of the test results shall be performed at the type test opening(s) and at the actual air volume flow rate in accordance with EN 14175-3:2003, 5.2.3 and 5.2.4.
If the air volume flow rate is other than that established in the type test, it shall be noted.
NOTE Such a deviation can affect the face velocity pattern.
If they do not want to remove the equipment, then you can only report what readings you get!
Last, but not least, the client should be concerned that the nature of the equipmemt layout is affecting flow rate to this extent and it will be thier decision on how to manage it.
If the type test data is average of 0.5 and your actual is substaintially below, you may have to issue a fail teat report!
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Rank: Forum user
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Rank: Forum user 
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The ops that use the fume cupboards in our labs do a weekly check with a vane anemometer, while the fume cupboards are equipped. The gist is the managers want to know that the flow rates are sufficient while operational.
We also have the company that installed them come and check them/service them on a routine basis (either every year or couple of years). I believe they prefer to do flow rate checks/balancing with the fume cupboards empty
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Rank: Super forum user
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J Scott wrote:I'm being asked to test fume cupboards with apparatus still in them As Andrew suggests above, it's logical for you to do the tests with the equipment in place; if the results are good then you know the equipment operators will be protected. And also, as Andrews notes, if you have a contract for regular maintenance, the cupboard manufacturers will want to know the extraction meets their specification - their specification will be for an empty cupboard. So the cupboards need testing under both conditions.
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Rank: Super forum user
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But its equally obvious, if the fume cupboards are so full of equipment, that the air flow and extraction could well be affected.
Maybe the fume cupboards are not big enough or consideration needs to be given as why so much equipment is kept in the fume cupboards in the first place.
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Rank: Forum user
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You might also want to try smoke tests - they can be used pretty well anywhere where you want to check air flows, such as asbestos containments or similar.
They can highlight any turbulence or non-laminar air flows and as Ian suggested, you might need to re-arrange the contents of your fume cupboards.
They can end up being a dumping ground for anything that can't be stored someplace else... Like jars of mercury...
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