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Frequently asked questions on Fume


Frequently Asked Questions

When do I need fume extraction?

The simple answer to this question is - when exposure to the fume and its component parts would, without the use of extraction, exceed the limits laid down by regulations. Although the regulations may have different names in different countries, they generally have similar requirements. These are, that welding fume generally, and the compounds that form its component parts, must not exceed certain concentrations in a worker's breathing zone when averaged over a reference period of time. These concentrations may again be known by different names, such as exposure limits or limit values, but the values are generally the same in different countries. To assess whether exposure is above the exposure limits, it is necessary to supply answers to the following questions.

To what level must the fume be controlled?

In many countries, exposure to welding fume must not exceed 5mg/m3 when averaged over an eight hour reference period, but with the proviso that none of the fume constituents exceed their own exposure limit. Thus, if fume contains substances with exposure limits less than 5mg/m3, e.g. nickel, chromium, cobalt, manganese etc. it is possible that the total fume will require control to levels significantly less than 5mg/m3 to maintain control of these more toxic elements. It is possible to calculate the concentration of welding fume, in mg/m3, at which any fume component will reach its occupational exposure limit using the formula:

100A / C mg/m3.

where A is the occupational exposure limit of the fume constituent and C is the concentration of A in the fume.

The lowest value solution to the above equation is the level to which the particulate fume must be controlled. Thus, fume of different compositions will require control to different levels and the requirements for extraction will vary accordingly, e.g. fume from stainless steel welding will require control to lower levels than fume from carbon steel welding.

Gases present in the fume will simply require control to their respective exposure limits.

What are the factors affecting exposure?

Factors which affect exposure and hence the possible requirement for extraction are:

  • The process - open arc processes, e.g. manual metal arc, metal inert and active gas welding, flux cored arc welding, cutting & gouging, produce the most fume.
  • The process parameters - increases in current, voltage and shielding gas oxidation potential usually generate more fume.
  • Welding position and location - welding positions which place the welder closer to the fume generally increase exposure. Welding in an open workshop would be expected, for the same activity, to result in lower exposures than working in a confined space.
  • Duration and frequency of exposure - higher duty cycles produce more fume and therefore increase exposure. Because exposure limits refer to average exposure for a reference time period, the duration of any period of exposure within the reference period affects the overall exposure.

How can a requirement for fume control be established and compliance with regulations verified?

A visual assessment of exposure to welding fume may be all that is needed to establish a requirement for extraction. If the control level for the particulate fume is low e.g. MMA welding of stainless steel or nickel alloys, then extraction will be required in almost all situations. Additional protection in the form of respiratory protection may be required in some cases. Only when the duration of exposure is very low, will extraction not be required.

When welding materials where the fume control levels are higher, and the extraction requirement consequently less, e.g. carbon steels, the situation is less clear but also less critical. Nevertheless, fume control will usually be required.

The assessment of exposure, and therefore the requirement for extraction, will often be a difficult decision. This is particularly the case with toxic gases where visual assessments are impossible and guidance or experience is required. Measurement may be necessary to establish whether extraction is required, or indeed, if extraction is already installed, whether additional control methods are necessary. In such cases, measurement should be performed according to nationally recognised standards e.g. EN ISO 10882 - 1 and 2 Health & Safety in welding & allied processes - sampling of airborne particles and gases in the operator's breathing zone. Part 1 Sampling of airborne particles. Part 2 Sampling of gases.

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