Breath of fresh air Bob Burns Dust and fumes compromise air purity in the workshop, so extraction is vital - especially with growing attention on Health and Safety issues from employers, employees and insurance companies. Air purity in the workshop is compromised by dust and fumes, so extraction is vital - especially with growing attention on Health and Safety issues in the workplace from employers, employees and insurance companies.

The fumes generated by welding, plasma cutting and mechanical grinding are a mixture of fine, airborne particles and toxic gases. For example, most welding fume arises from the wire or rod electrode as it is vaporised for transfer over to the work piece.

Some of the fume will consist of 'respirable' particles; particularly damaging to lungs, these are only a few microns in size, like the hazardous particles in coal and cement dust. The gases produced as a by-product of welding include ozone, nitric oxide, nitrogen dioxide and carbon monoxide.

The quantity and composition of welding fume depends on welding technique; wire diameter and composition; electrical current and voltage; and the rate of flow and composition of the welding gas. Also 'pyrolsis' products (including oils, hydrocarbons, lead and zinc) can be released, particularly when welding or cutting coated or oily surfaces.

Inhalation of welding and cutting fumes can have short and long term effects. Inhaling metal oxides, particularly zinc and copper (prevalent when welding galvanised steel) can result in metal fume fever; this has flu-like symptoms but no long-term effects - so long as the hazard is removed.

However, prolonged inhalation of fumes, dust and gases can cause irritations to the upper respiratory tract and chronic bronchitis - especially in smokers; there's actually a bronchpulmonary illness called 'welder's lung.'Also, there is a belief that those who weld special steels containing nickel and chromium are more exposed to the risk of lung cancer.

There's no hard evidence to support this, but Ni and Cr compounds have been associated with lung cancer when used in other industrial processes; so common sense dictates the prompt extraction of such fume.It's best to extract fume as close as possible to the source, while not obscuring the worker's view and presenting other risks.

Health and safety regulations require all welding and plasma cutting work stations to be equipped with local extraction systems that conform to community directives 626/94 (art 21 and 22); the system must have a speed-of-capture (at the point of emission) of not less than 0.5m/s.Fume extraction solutions include single intake stations, centralised systems, wall- and ceiling-mounted installations, and portable units.

Indeed, a fume extraction 'solution' could be something the size of a vacuum cleaner or form an integral part of the workshop.Within the system, a factor for consideration is filter type:* Mechanical: essentially a paper membrane, this is a low-cost means of extracting dust (but not gases) from the atmosphere - but if there is oil vapour in the air (say from machining elsewhere in the workshop) paper filters soon clog and become ineffective.

* Active carbon: more expensive than paper filters, but longer lasting and better at absorbing gases.* Electrostatic: typically the most expensive solution but the most effective.

Choice of fume extraction solution (including type, filters, pipes and hoods) will typically be governed by the location and size of the work pieces. Each supplier tends to have its own rules-of-thumb on specifying fume extraction systems, so it's worth contacting them for advice.

Also quantity and composition of welding fume will depend on factors including welding technique; wire diameter and composition; electrical current and voltage; so it's also worth contacting the welding and cutting equipment manufacturers, as they will be able to provide the best advice and best appreciate your working environment.Bob Burns is the managing director of Butters AMT.