Fume and Gases

Welding Fume and Gases

Welding fume is an unavoidable by-product of MMA welding. The welder should be aware of what fume is likely to be generated while welding is taking place and the potential hazards associated with exposure to that fume.

Fume consists of particulate fume (the part you can see) and gaseous fume (the invisible part occasionally smelled).

Particulate Fume

Particulate fume is commonly formed from vaporisation of the welding consumable. The composition of particulate fume produced by MMA welding depends on the composition of the consumable, the type of coating on the electrode and, to a lesser extent, on the composition of the material(s) being welded.

The following statements give a general indication of what the constituents of the particulate fume are likely to be.

Fume from MMA-welding aluminium is mostly aluminium oxide, chlorides and fluorides. The MMA process is seldom used for welding aluminium, but the coatings used are particularly active and can produce toxic fume.

Fume from MMA-welding steel is mostly iron oxide with a small amount of manganese oxide and other alloying elements. Basic coated electrodes will also produce fluorides in the fume.

Fume from MMA-welding stainless steel contains chromium, the majority being hexavalent chromium, and nickel, as well as iron and manganese. Basic coated electrodes will also produce fluorides in the fume.

Fume from MMA-welding copper alloys contains copper oxide, fluorides plus other elements depending on the specific alloy being welded.

Fume from MMA-welding nickel alloys contains nickel, fluorides and other elements depending on the specific alloy being welded.

When MMA-welding materials containing zinc, such as galvanised iron and steel, the fume may bring on an attack of metal-fume fever.

The amount of particulate fume produced depends on the electrode diameter, coating type and welding current. Generally, the higher the current for a particular diameter of electrode, the greater the amount of fume generated. Cellulosic and basic coated electrodes also tend to generate more particulate fume than rutile types.

Gaseous Fume

With MMA welding, there is very little gaseous fume produced under normal circumstances. Cellulosic electrodes do produce carbon dioxide but with good general ventilation, this is not likely to present a significant hazard.

Exposure to Fume

Whilst all components of welding fume may present a risk to health in high-enough concentrations, some present a greater hazard than others. The potential effect of exposure to welding fume depends upon:

The composition of the fume
The volume of fume produced
The length of time the welder is exposed to the fume
Any medical conditions the welder may have such, as being asthmatic

Commonly-encountered pollutants in MMA welding, thought to carry the highest risk factors, include chromium in its hexavalent form, nickel and fluorides. In order to keep exposure to an acceptable level, the following guidelines should be observed:

The welder can minimise exposure by ensuring that his head position is away from the rising plume.

By using a suitable-sized electrode, the correct arc length and setting a welding current within the manufacturer’s recommended range, the welder can prevent excessive particulate fume being generated. Correct use of fume-extraction equipment significantly reduces fume exposure.

The use of respiratory protection is recommended when dealing with hexavalent chromium.

Welding can give rise to electric shock, excessive noise, eye and skin burns due to the arc rays, and other health hazards if fumes and gases are inhaled.

Over-exposure to the fumes and gases can give rise to dry nose, throat and eyes. Respiratory irritation and in some cases, longer-term health effects such as lung deposits can be caused.

Read all the manufacturer’s instructions to achieve the correct welding conditions and ask your employer for the relevant materials Safety Data Sheets (SDS).

For eye protection and body protection, always wear a welding visor with the correct filter lens, and suitable welding gloves and clothing to prevent injury from burns, radiation, sparks, molten metal and electric shock. See pages 264–301

Wear ear protection when required.

Adequate ventilation to prevent an accumulation of fumes and gases should be used. Where fume levels cannot be controlled below the recognised exposure limits, use local exhaust to reduce fumes and gases; in confined spaces without adequate ventilation, an air-fed breathing system should be used; outdoors, a respirator may be required.

Precautions for working in confined spaces should be observed: