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Health, safety and accident prevention - welding fume assessment

   

jk30a.jpgGuidelines are given on the principal health and safety considerations to ensure safe welding practices and prevent accidents. Health risks associated with fume and gases generated during welding are highlighted.

What is welding fume/gases?

Welding fume is a mixture of airborne fine particles. Toxic gases may also be generated during welding and cutting.

Fume

More than 90% of the fume arises from vaporisation of the consumable electrode, wire or rod as material is transferred across the arc or flame. The range of welding fume particle size is shown in relation to more familiar types of dust and fume. The respirable fraction of particles (especially less than 3µm) are potentially more harmful as they can penetrate to the innermost parts of the lung.

The range of welding fume particle size in relation to more familiar types of dust and fume
The range of welding fume particle size in relation to more familiar types of dust and fume

Gases

Gases encountered in welding may be:

  • Fuel gases which, on combustion, form carbon dioxide and, if the flame is reducing, carbon monoxide
  • Shielding gases such as argon, helium and carbon dioxide, either alone or in mixtures with oxygen or hydrogen
  • Carbon dioxide and monoxide produced by the action of heat on the welding flux or slag
  • Nitric oxide, nitrogen dioxide and ozone produced by the action of heat or ultraviolet radiation on the atmosphere surrounding the welding arc
  • Gases from the degradation of solvent vapours or surface contaminants on the metal.

The degree of risk to the welder's health from fume/gases will depend on:

  • composition
  • concentration
  • the length of time the welder is exposed

Health hazards from particulate fume

The potential hazards from breathing in fume are:

Irritation of the respiratory tract

Fine particles can cause dryness of the throat, tickling, coughing and if the concentration is particularly high, tightness of the chest and difficulty in breathing.

Metal fume fever

Breathing in metal oxides such as zinc and copper can lead to an acute flu-like illness called 'metal fume fever'. It occurs most commonly when welding galvanised steel; symptoms usually begin several hours after exposure with athirst, cough, headache sweat, pain in the limbs and fever. Complete recovery usually occurs within 1 to 2 days of removal from the exposure, without any lasting effects.

Longer term effects

The continued inhalation of welding fume over long periods of time can lead to the deposition of iron particles in the lung, giving rise to a benign condition called siderosis.

There is evidence that welders have a slightly greater risk of developing lung cancer than the general population. In certain welding situations, there is potential for the fume to contain certain forms of chromium and/or nickel compounds - substances which have been associated with lung cancer in processes other than welding. As yet, no direct link has been clearly established. Nevertheless, as a sensible precaution and to minimise the risk, special attention should be paid to controlling fumes which may contain them.

Additional hazards

A number of other specific substances known to be hazardous to health can be found in welding fume such as barium and fluorides which do not originate from the metal. If the metal contains a surface coating, there will also be a potential risk from any toxic substances generated by thermal degradation of the coating.

Health hazards from gases

The potential hazards from breathing in gases during welding are:

Irritation of the respiratory tract

Ozone can cause delayed irritation of the respiratory tract which may progress to bronchitis and occasionally pneumonia.

Nitrogen oxides can cause a dry irritating cough and chest tightness. Symptoms usually occur after a delay of 4 to 8 hours. In severe cases, death can occur from pulmonary oedema (fluid on the lungs) or pneumonia.

Asphyxiation

jk30c.gif

Special precautions are needed when welding in confined spaces where there is the risk of asphyxiation due to the build up of inert shielding gases.

Carbon monoxide, formed as a result of incomplete combustion of fuel gases, can also cause asphyxiation by replacing the oxygen in the blood.

Establishing safe levels of fume in the workplace

Much of the regulatory framework applied to welding and allied processes is directed towards protecting the health of workers by maintaining their exposure to fume and gases within defined limits known as exposure limits. In the UK these limits are known as Workplace Exposure Limits (WELs). They are for use with the Control of Substances Hazardous to Health Regulation and are published annually in EH/40 from the Health and Safety Executive.

WELs are concentrations of hazardous substances in the air, averaged over a specified period of time referred to as a time weighted average. Two time periods are used: long term (8 hours) and short term (15 minutes). Short term exposure limits (STELs) are set to prevent effects, such as eye irritation, which may occur following exposure for a few minutes.

Regulation 7(7) of COSHH states that 'without prejudice to the requirement to prevent exposure, control of exposure to a substance hazardous to health shall only be treated as adequate if:

  1. the principles of good practice for the control of exposure to substances hazardous to health set out in Schedule 2A are applied;
  2. any workplace exposure limit approved for that substance is not exceeded; and
  3. for a substance -
    1. which carries the risk phrase R45, R46 or R49, or for a substance or process which is listed in Schedule 1; or
    2. which carries the risk phrase R42 or R42/43, or which is listed in Section C of HSE publication Asthmagen? Critical assessments of the evidence for agents implicated in occupational asthma as updated from time to time, or any other substance which the risk assessment has shown to be a potential cause of occupational asthma, exposure is reduced to as low a level as is reasonably practicable.

The risk phrases R45, R46 and R49 refer to substances that may cause cancer or heritable genetic damage. The risk phrases R42 and R42/43 refer to substances that may cause sensitisation by inhalation or by sensitisation and skin contact.

The eight principles of good practice for control of exposure to substances hazardous to health, as reproduced from the COSHH Regulations 2002 (as amended). Approved Code of Practice and guidance, are shown below:-

  1. Design and operate processes and activities to minimise emission, release and spread of substances hazardous to health;
  2. Take into account all relevant routes of exposure - inhalation, skin absorption and ingestion - when developing control measures;
  3. Control exposure by measures that are proportionate to the health risk;
  4. Choose the most effective and reliable control options which minimise the escape and spread of substances hazardous to health;
  5. Where adequate control of exposure cannot be achieved by other means, provide, in combination with other control measures, suitable personal protective equipment;
  6. Check and review regularly all elements of control measures for their continuing effectiveness;
  7. Inform and train all employees on the hazards and risks from the substances with which they work and the use of control measures developed to minimise the risks;
  8. Ensure that the introduction of all control measures does not increase the overall risk of health and safety.

If employers apply the principles correctly, exposure should be below any relevant WEL. Control by personal protective equipment should only be used when other measures are not reasonably practicable.

The WELs of some of the substances found in welding fume are listed in Table 1; the absence of other substances from this list does not indicate that they are safe.

Workplace Exposure Limits

Substance8hr TWA15 min STEL
Beryllium & beryllium compounds (as Be) 0.002 mg/m 3  
Cadmium oxide fume (as Cd) 0.025 mg/m 3  
Chromium VI compounds (as Cr) 0.05 mg/m 3  
Cobalt & cobalt compounds (as Co) 0.1 mg/m 3  
Nickel (insoluble compounds) 0.5 mg/m 3  
Fluoride (as F) 2.5 mg/m 3  
Iron oxide, fume (as Fe) 5 mg/m 3 10 mg/m 3
Manganese, and its inorganic compounds 0.5 mg/m 3  
Ozone   0.2 ppm
Nitric Oxide 1 ppm  
Nitrogen dioxide 1 ppm  
Chromium III compounds (as Cr) 0.5 mg/m 3  
Barium compounds, soluble (as Ba) 0.5 mg/m 3  
Carbon monoxide 30 ppm 200 ppm
Copper fume 0.2 mg/m 3  

Expertise and resources

Welding fume exposure database

Welding fume

Publications and relevant standards

EH 40
EH 55
Workplace Exposure Limits, HSE Books.
The Control of Exposure to Fume from Welding, Brazing and Similar Processes, HSE Books, 1990.

For more information, please contact us.

This Job Knowledge article was originally published in Connect, September 1997. It has been updated so the web page no longer reflects exactly the printed version.

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