Part 11: Hazardous Substances

Hazards From Metals Used in Welding

Metal fumes generated during welding range in toxicity. Because fumes from different metals are combined in the welding plume, it is clear that avoidance of the plume is the best protection against inhalation.

Aluminium:Fume group A (least toxic). Exposure to aluminium fumes may produce some lung effects. There is no clear picture of the dose required (concentration x time) for these to occur.

Barium:Fume group C (highly toxic). Water or acid soluble barium compounds are extremely poisonous. Fumes containing barium may result in a lung condition called baritosis which is one of the benign pneumoconioses in which inhaled particulate matter lies in the lungs for years without producing symptoms. Baritosis produces abnormal physical signs including incapacity for work, interference with lung function, or liability to develop pulmonary or bronchial infections or other thoracic disease.

Beryllium:Fume group D (extremely toxic). Used mainly as an alloy with other metals, beryllium is deadly and extreme precautions must be taken. This metal must be welded in inert atmospheres, inside airtight enclosures, with the welder outside.

Cadmium:Fume group D (extremely toxic). Used in electroplating and as an alloy with metals, cadmium is also an ingredient in some paints. A single exposure to cadmium oxide fumes can cause fatal lung irritation.

Chromium:Fume group C (highly toxic). The oxidation of chromium alloys can produce chromium trioxide fumes, often referred to as chromic acid. These fumes may produce skin irritation as well as bronchitis and other problems.

Cobalt:Fume group C (highly toxic). Milling tungsten carbide tips (during saw sharpening) can cause airborne dust concentrations great enough to lead to 'hard metal' respiratory disease. Cobalt (a binder ingredient) is considered a crucial factor in producing this disease, though this may involve an interaction with the tungsten carbide itself.

Copper:Fume group B (toxic). Like zinc, Inhalation of copper fume may cause 'metal fume fever'.

Iron:Fume group A (least toxic). Prolonged, heavy exposure to fumes from welding iron articles can result in a condition called siderosis, with visible changes on an x-ray but no changes in lung function.

Lead:Fume group C (highly toxic). Poisoning generally results from inhalation of fumes, although the swallowing of dust is also a cause. Lead-based paints are a source of lead fumes, especially when old steel structures are cut or welded. Signs and symptoms of lead poisoning may include abdominal pains, constipation, headaches, weakness, muscular aches or cramps, loss of appetite, nausea, vomiting, weight loss, and anaemia. In severe cases, it can be fatal.

Magnesium:Fume group B (toxic). The oxide fumes from magnesium can produce metal fume fever, which is characterised by influenza-like symptoms.

Manganese:Fume group B (toxic). Manganism is a serious occupational disease but its link to welding is controversial.

Mercury:Mercury vapour can be produced by welding or cutting metals coated with protective materials containing mercury compounds, such as the antifouling paints used on ships' hulls. Nowadays, less toxic substitutes are used in place of mercury, but there will still be some vessels in service which are protected with mercury-containing antifouling compounds. Exposure to mercury vapour may result in abdominal pain, vomiting, diarrhoea, and other serious problems which, collectively, can result in death.

Nickel:Fume group C (highly toxic). Often used as an undercoating on chrome-plated parts, nickel and its compounds are generally considered to have low toxicity.

Silver:Fume group C (highly toxic).

Tin:Fume group A (least toxic).

Titanium:Fume group A (least toxic). Dust may irritate the respiratory tract in high concentrations.

Tungsten:Fume group B (toxic). Milling tungsten carbide tips (during saw sharpening) can cause airborne dust concentrations great enough to lead to 'hard metal' respiratory disease. Cobalt (a binder ingredient) is considered a crucial factor in producing this disease, though this may involve an interaction with the tungsten carbide itself.

Vanadium:Fume group C (highly toxic). Dust and vanadium pentoxide fumes may cause severe eye, throat and respiratory tract irritation and pain.

Zinc:Fume group B (toxic). Welding, brazing, or flame cutting of galvanised steel causes zinc oxide fumes. Inhalation of these may result in metal fume fever.

Fluorides

These and other toxic compounds of fluorine may be found in some welding and brazing fluxes, electrode coverings and submerged arc fluxes. Containers are labelled to warn of the presence of fluorides. The fumes will cause chills, fever, painful breathing, and coughs if inhaled. Over a long period, fluoride can build up in the bones, causing them to lose calcium and become brittle.

Hazards from Gases Generated by Welding Processes

The following gases are generated from welding processes and are particularly serious hazards that must be protected against.

Nitrogen dioxide:Formed in the welding arc directly from the air, nitrogen dioxide is very irritating to the eyes and mucous membranes of the lungs and throat. Exposure to concentrations between 200 ppm and 700 ppm (parts per million) can be fatal. Lower concentrations may produce only mild bronchial irritation, but will be followed several hours later by acute pulmonary oedema (fluid in the lungs).

Phosgene:This gas is produced when residues of chlorinated hydrocarbon degreasers, such as trichloroethylene and perchloroethylene, are left on metal being welded or flame-cut. The heat and the ultraviolet radiation cause the degreaser to decay into phosgene gas, which was used as a poisonous gas in the First World War. Freon gas, which is used in many refrigeration plants and as a propellant in aerosol cans, will also decompose to form phosgene when exposed to ultraviolet rays. Phosgene will produce skin inflammation. Inhalation of high concentrations will cause pulmonary oedema. Death may result through respiratory or heart failure.

Phosphine:When steel which has been coated with a phosphate rust-proofing is welded, phosphine gas is generated. High concentrations will irritate the eyes, nose and skin. Very high concentrations can result in severe damage to kidneys and other organs, and perhaps death.

Ozone:A gas produced by the ultraviolet radiation in the air in the vicinity of arc welding and cutting operations, ozone is very irritating to all mucous membranes. Excessive exposure produces pulmonary oedema. Other effects of exposure include headache, chest pain, and dryness of the respiratory tract.

Agents for Cleaning and Passivating Stainless Steel

These substances are both very dangerous and will require specialised methods of storage, use and disposal:

• nitric acid
• hydrofluoric acid.

Part 12: Metal Preparation

The methods used to prepare metals for welding pose a series of specific hazards, each of which requires control. See TN7 chapter 10 for further details.

Abrasive Blasting

This poses hazards to the eyes, lungs and hearing through noise, vibration and dust creation. Abrasive blasting needs to be carried out in a blasting cabinet with ventilation.

Mechanical Preparation

Power tools (grinders and nibblers) can pose hazards of eye injury, vibration injury and electric shock.

Use of Degreasing Chemicals

There may be exposure to the solvent vapour or to its decomposition products (phosgene). Solvent vapours may be flammable and explosive. Skin contact can result in occupational dermatitis. See the AS 1627 series.

Cleaning with Caustic or Acid Solutions

These can pose hazards of contact with the solution or its corrosive and/or irritant fumes. Hydrogen gas can be generated. Hydrofluoric acid poses extreme dangers and should be used only with specific precautions.

Contaminated Surfaces

When coatings on metals are heated it should be assumed that the decomposition products are toxic.

Part 13: Welding in Confined Spaces

TN7 chapter 20 deals with this topic and refers to AS 2865. A confined space is:

any space that is not intended as a regular workplace AND has restricted means of entry/exit AND has inadequate ventilation.

Key elements of safe welding in confined spaces include the following.

Access and Emergency Rescue

A trained, alert observer must be stationed outside the space.

Safe access is required and pre-planned emergency rescue (including a safety belt or lifeline) must be assured through the use of suitable emergency equipment.

Electric Shock

Risks of electric shock are increased when working in confined spaces. A range of measures are described in TN7, including having an observer outside the space with access to a cut-off switch and rescue equipment. Always site the welding equipment outside a confined space.

Ventilation

Ventilation for welders in confined spaces is of clear importance. Local exhaust ventilation will be needed. Don't enter a confined space unless you are sure the atmosphere is safe.

Atmosphere Testing

The atmosphere in a confined space may become rapidly depleted in oxygen content. Check with a monitoring device before entry. As welding proceeds, inert gases may rapidly displace oxygen - check the atmosphere with a continuous monitor located near the welder's breathing zone. Check for toxic or explosive atmospheres, if appropriate.

Arc Flash

Reflected arc flash in a confined space may affect bare skin (e.g. the back of the neck).

Fire Protection

A fire in a confined space will be more serious than a normal fire.

Heat Stress

Confined spaces may be hot because of solar load (if outside), or may become hot during the pre-heating of metals. Take precautions to prevent heat affecting the worker. Cool air is one option but may not provide sufficient protection against radiant heat from hot surfaces. Working in a confined space (especially if hot) can affect a welder, given the level of protective equipment required and it may be necessary to limit the welder's working time.

Permit to Work

Welding in a confined space may be subject to a permit to work. An example is available below.

Form is available as pdf [size: 42k] or rtf [size: 56k] or word [size: 42k] or gif [size: 37k]

Part 14: Hot Metals Sparks

Hot metal sparks are a constant hazard in many welding processes.

Essential safety measures are to ensure:

• good housekeeping
• training in the selection and use of fire-fighting equipment
• prevention of sparks entering clothing/boots through the use of flame-resistant personal protective equipment.

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