Fume, Dust, Vapour and Gases From Welding Process

• their chemical nature
• their particle size (in the case of dusts and fume)
• their solubility
• the quantity absorbed
• the duration and frequency of exposure
• the occupational environment
• the susceptibility of the individual.

Particle Size and Behaviour

Dusts and fume are suspensions of finely divided solid particles in the air. Their diameter determines how long they remain in the air and how far down the respiratory pathway they can reach. Particles above 100mm diameter fall very quickly and remain near the point of emission. They are unlikely to be inhaled. Particles in the range 30 to 100mm also fall out quickly but can be carried further by air currents. At the smaller diameter end of the range particles can be inhaled, but will be trapped by the filtering mechanism in the nose. They are unlikely to be absorbed unless they are soluble in water.

In the range 5 to 30mm, particles remain airborne for some time. On inhalation they will reach the bronchial part of the respiratory system. From there they will be cleared by the ciliary mechanism.

Areas of the respiratory tract reached by particles.

Particles below 5mm will be carried into the air sacs in the alveolar region. They are removed only slowly from this region. However, particles that are less than 1mm in diameter will frequently remain suspended in the air and be expelled with the exhaled air.

Humans are particularly at risk from the inhalation of substances, first because they cannot stop breathing and second because the quantity of air breathed in a day is very large. Thus even small concentrations of a substance in the atmosphere have the potential to affect the health of the individual. Gases and vapours are inhaled deep into the alveolar region. Their effect depends primarily on their chemical nature.

The welder may be exposed to a wide variety of dusts, fume and gases. Some welding and cutting operations generate large quantities of fume. The size range of the particulates produced spans all those referred to above and can be compared to other airborne particulates.

Sizes of particles.

In the welding environment, sources of substances that can be a respirable hazard include:

• Welding
  • the parent metal,
  • the filler and its flux,
  • shielding gases,
  • the action of the heat source on the environment,
  • surface contaminants;

Health Effects of Inhaled Substances

The manufacturers of welding consumables and the suppliers of gases are required to supply data sheets, giving details of the harmful effects, if any, that the products present. They also generally supply typical figures representing the approximate composition of the fume when used under typical conditions. It should be borne in mind that the data sheet for a substance or preparation may not foresee all the conditions in the workplace – it may not, for example, give the breakdown products that are likely to arise close to an arc. Even a totally innocuous substance, if inhaled in sufficient quantity, can interfere with the efficiency of the lungs. Many of the substances that are inhaled in a welding environment are irritants, that is, they produce local swelling and reddening of the surface of the part of the body exposed.

Some substances are toxic when inhaled, producing immediate or chronic effects. They may be absorbed into the blood stream and carried around the body to a target organ such as the liver or the kidneys. Chronic effects, for a few substances, can include cancer.

A few substances can produce sensitisation by inhalation or by skin contact. Substances that cause sensitisation by inhalation give rise to an allergic form of asthma.63,64 Cases of asthma associated with isocyanates, or with solder fluxes containing colophony, are relatively common. Cases of asthma associated with welding stainless steel are also reported. Skin contact with such substances can give rise to allergic dermatitis.

A number of metals give rise to an illness known as metal fume fever. This manifests itself as a flu-like illness which comes on some hours after exposure, with a fever, aches and pains. Sufferers usually make a full recovery if the cause was a metal such as zinc, but the outlook can be more serious if the cause was exposure to a toxic metal such as cadmium. In case of doubt, medical attention should be sought promptly.

Reference: Health and Safety in Welding and Allied Processes by Jane Blunt and Nigel C Balchin