Posted By Chris Packham
This is not quite as simple to answer as may at first appear. It will depend upon the actual design of the LEV, and in particular the capture system. There is an extremely good demonstration done by Mark Piney of HSE which shows how important the design of the capture system is. With an inadequate capture system, increasing air flow will have little or no effect on capture of fume or vapour.

I suggest you take a look at HS/G 37 which will explain this.

With solder fume I have found downdraft benches to be the most effect solution. They need little energy, do not obstruct the worker and effectively remove the contaminant. There is even a bench-top system marketed by Axminster Tools that a client installed with considerable success.

If you need more feel free to contact me direct.

Chris

Posted By Chris Packham
Steve

In essence the same considerations will apply to fumes from epoxy glues. One question that I always ask myself is: "Is the contaminant heavier than air?" If the answer is "yes" then my immediate response is to see if I can work with gravity, rather than against, i.e. draw down rather than up. In my experience this is almost always more effective and requires less energy.

Chris

Posted By Chris Packham
Barrie,

The tube attached to the tip of the soldering iron can work, but I have never been fully satisfied with these.

One problem is that the tube itself is of relatively small diameter and can easily become partially clogged by an accumulation of flux condensing on to the walls. This significantly reduces the system's effectiveness. The system also appears to be easily affected by ambient air currents and actual movement of the tip whilst soldering.

I had a client who found these an almost continuous source of irritation due to the need to clean out the tube and associated hose at frequent intervals. They switched to a downdraft bench and found this much more satisfactory. The downdraft bench was a simple system that was merely placed on to the workbench and attached to the extraction system. Virtually no maintenance was now required, quickly recouping the very limited investment required.

If this is of interest contact me direct and I can give you chapter and verse on where these can be obtained.

Chris

Posted By Paul Bibby
Hi Barrie,

Getting back to your original questions:

1. Anything from 1 to 2 m/s at the tip will be sufficient to move solder fumes. Problem is most LEV systems (Nederman systems for example) generate face velocities much higher than that, which can interfere with the soldering process (reduces tip temperatures). One recent study (http://www.hse.gov.uk/research/hsl_pdf/2005/hsl0519.pdf) found tip extraction systems generating face velocities of between 5 and 100+ m/s depending up on the cross-sectional area of the aperture. Much higher than necessary and almost guaranteed to annoy the solderer.

All properly designed metal fume LEV systems work on the principle of 'high velocity-low volume' and this requires the LEV aperture to be small and as close to the solder tip as possible. A significant issue, therefore, is the fact that these systems rely heavily on the operator using them properly. In my judgement this is a hit and miss affair and other complimentary steps should be taken to improve overall control.

Lead-free solders are not hazard free - many contain Silver, Antimony, Bismuth, Copper, Zinc, and Indium in various quantities - all are hazardous in fume form, some arguably more so than Lead. Antimony, for instance. MSD sheets do not tell the whole story but they do help move things forward. Check this one for instance http://www.kester.com/MS...%20Free%20Solder%20US%20(24Mar06).pdf

If you are using rosin/colophony free solders and can tolerate the higher melting points of lead free solder then I would recommend using these as a matter of course. You will still require a suitable LEV system that the operator is correctly trained and instructed to use but its proper use is less critical than with Lead solder. It is essential to monitor the operator to ensure he uses the LEV correctly. I assume the flux your guys use is rosin free too.

Once you have an LEV in place you are legally obligated to keep it maintained - this includes making sure it is working correctly i.e. maintaining the adequate velocity at the tip.

The best off the shelf systems I have recommended are produced by Nederman. They are not tip extraction systems, which are the best overall, but they are good for small volume work such as yours.

2. Epoxy resin vapours require 'high volume-low velocity' extraction and will not be removed by the Solder Tip LEV system. A face velocity of 0.5 m/s will be sufficient to remove the vapours. The critical issue is the design of the LEV.

As I don't have sufficent info on the quantities involved I will assume the worse - using a few litres or more of resin daily. My recommendations may be grander than is necessary but the principles remain the same for smaller quantities.

The adhesive work should be done at the very least in a partially enclosed system. The air should be drawn from the front of the bench towards the LEV duct at the rear of the bench. The design would partially enclose the bench at the sides, rear and above the bench. The operator would work by reaching into the enclosure to do the work but not putting his head in it, for obvious reasons. The open front of the enclosure forms the face of the LEV where the face velocity if measured. 0.5 m/s is sufficient to move the vapours away from the operative. Ideally, the contaminated air should be passed through a suitable filter (i.e. activated charcoal) before it is exhausted to atmosphere.

regards,
Paul