Plasma cutting mild steel, stainless steel, and other metals creates fumes, gases and fine particulate dust that, when left uncontrolled, are harmful to operators, machines, and electronics.
Why Are Plasma Fumes, Dusts & Gases Dangerous?
A number of health risks are caused by the dust, fumes and gas generated by plasma cutters. The nature of fume depends upon the metal being cut and upon any coatings. Cutting of stainless steel is potentially the most hazardous as the fumes will contain chromium and nickel. Copper and its alloys are also commonly cut and can also produce a significant fume hazard. The risks from fumes should be assessed in accordance with HSE Guidance.
Oxides of nitrogen are formed during plasma cutting and could accumulate in areas of poor ventilation. These are likely to be most significant during plasma cutting where air or nitrogen is used as the plasma gas. Ozone is most likely to be formed during cutting of aluminium or stainless steel.
Where inert gases are used they may accumulate in confined spaces causing an asphyxiation risk. This is most likely to occur when the gas is significantly heavier than air, eg argon/nitrogen mixtures.
In poorly ventilated areas, flammable gases may also produce a fire risk.
Gases, particularly oxides of nitrogen, are a more significant hazard at hand-held cutting than at mechanised cutting as the operator is in close proximity to the torch.
Controlling Plasma Cutting Fumes with LEV
In workspaces where plasma cutting occurs and there is an identified risk, a Local Exaust Ventilation (LEV) system should be put in place.
Plasma cutting can be mechanised or operated manually, LEV requirements will depend on the specific type of plasma cutting being carried out:
Handheld Plasma Cutting
Handheld plasma cutters, consisting of a torch and power source, are manually operated and typically used in fabrication and vehicle repair. LEV should be installed to prevent inhalation of the dust and fumes generated during operation. Plasma cutter LEV systems require higher air volumes for controlling fumes than welding and the dust loading of plasma is much higher, because of this, systems similar to those used to control welding fumes can be inappropriate. The LEV should be position as close as possible to the source of the contaminants and will require constant adjustment during long cuts.
Mechanised Plasma Cutters
The powerful arc of plasma cutting results in most fumes being emitted below the plate being cut. As a result, down draft high volume local exhaust is necessary for effective control if dry cutting is carried out.
At mechanised cutting, local exhaust ventilation (LEV) can be built into the table supporting the cutting grid or bed. A capture velocity of at least 0.75 metres/sec measured at the position where the fume is produced will be required to ensure adequate control.
As mechanised cutting beds are often large, this could result in very high volumes of air being extracted. Designs are available which utilise a series of chambers built into the table. The position of the cutting torch actuates dampers which creates air flow only in the chambers in the vicinity of the torch. An alternative design connects the chambers to the exhaust duct via a section of duct which moves in sequence with the torch along a fixed duct with a slotted rubber cover. Systems of this type will require increased maintenance in order to ensure effective operation.
Detailed design and operation of down draft exhaust tables need to take account of the potential for damage by spatter and offcuts.
Underwater Plasma Cutting
Cutting underwater is a particularly effective control measure. This is capable of reducing noise levels to below 80dB(A); of reducing fumes levels to 10% or less of the dry equivalent; and of some reduction in levels of oxides of nitrogen. These levels of reduction can normally be achieved by cutting under 50mm of water. Further but less significant reductions can be achieved by additional submersion. However, even these levels of control may leave some residual risk from gases which should then be controlled by local exhaust ventilation around the torch.
Other advantages of underwater plasma cutting are a reduction in ultraviolet radiation and a reduction of thermal distortion particularly of thinner plate.
What Can RCS Do For You
RCS's engineers will endeavour to provide you with the most effective and cost-efficient solution for plasma cutting fume extraction, fully COSSH compliant, following current HSE guidelines and your own individual requirements. Call us on +44(0)1563 546807 or click here to contact us for more information.