The Case for Downdraught
For safe application within the spirit of the COSHH Regulations, down draught technology is the ideal way forward where dust and fume extraction is a key concern.
This, in simple terms, is because alternative technologies predominantly pull gasses and debris upwards – dragging them past the operator’s face and, in doing so, further contaminating the breathing zone, or are difficult to use whilst maintaining productivity.
It is a sad indictment, but the extraction marketplace has traditionally been dominated by conventional design approaches and procedures, which, in some cases work but often fail to provide true financial or in-
Yet, even when long established criteria for hood or arm velocities are deployed in the designs of these systems, it is often not known whether they will or will not work on the specific task until they are commissioned. By this time, of course, the client or has committed to a hefty investment -
It makes no sense, then, to hope that the pollutant can be picked up a practical distance away from its source to allow continued working, say 400mm from a slot or 600 – 800mm from a hood, when in the vast majority of cases gravity will have gained control long before. *
Even welding fume loses its buoyancy extremely quickly when mixed with ambient air -
So, it is much better to “go with the flow” and entrain pollutants as nature intended: downwards! In predictability terms, many extraction projects are delivered by experienced engineers using textbook recommended methods that simply fail to properly function on the specific issue or, worse still, have been designed for a quite different application. Typically such projects include the installation of an arm or other dust extraction initiative where the face velocity is, for instance, too low to capture the dust and “in-
Properly developed down draught bench systems are predictable. They can be demonstrated on site, or in the showroom on the actual process and velocities and therefore volumes can be adjusted easily and quickly to match the customer’s particular task. While, in extraction systems, it is often considered that there is no such thing as too much air, it is equally often the case that too much air can be deleterious to the process and indeed shorten the filter life and push up operating costs; so the ability to match air need to actual delivery is significant. Importantly, a downdraught bench can in the vast majority of cases be substituted readily for the existing work bench – whether or not operative seating is required (with our AirBench solution, AirBench Ltd has both variants readily available).
As soon as an AirBench downdraught bench is switched on it works! Operatives have no need to interfere with it, as it will require no adjustment. Indeed, it will not even be easily offended by acts of minor sabotage; for instance where partially blanking a unit off almost always results in improved performance in the area of work, by increasing the Down Draught velocity.
Even in welding applications, such action fails to damage the gas shield as the velocities used for effective capture of welding fume are relatively low and many, many installations have proved that whilst this is a natural concern for welders it is not in fact well founded. On the other hand, high vacuum “on torch” or close proximity arms can be much more of a problem.
It is our opinion, then, that down draught technology is -
But this is not the case with series produced such as AirBench which overcome the objections of one off designs whilst supplementing, not defying, the laws of gravity – without putting Client, process or investment at risk.
its own diameter of the source of fume, and that a slot system will only work up to