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Welding

Published: 01st Jan 2005 in Health and Safety International

To the inexperienced health and safety practitioner, welding operations can at first appear confusing, with the terms MIG, TIG and MMA frequently used around the workshop.

It is important that the fundamental principles of welding be grasped before the health effects of the operations can be assessed and quantified and workplace controls implemented.

The adverse health effects generated as a result of exposure to welding operations can vary greatly from the inhalation of dust and fumes, poisoning through accidental ingestion, noise, and exposure to UV light. The health effects associated with one type of welding activity can vary from the health effects associated with the next. Therefore it is important to understand the different types of welding processes used within today’s workplaces.

There are many types of welding, each presenting slightly different risks to the health of the welder. Approximately 95% of all welding operations fall into one of five categories:

• Gas Welding • Electric Arc Welding • Inert Gas Arc Welding • Resistance Welding • Soldering and Brazing

Gas welding

Gas welding, also commonly referred to as oxyacetylene welding, involves the combustion of oxygen and acetylene which produces a relatively hot flame (at a temperature of approximately 3000ºC). A rod of filler metal is used which is melted in the flame, and the molten metal flows into the joint being welded. Cast iron, mild steel, some stainless steels, aluminium, copper, tin, bronze and cupronickel can all be welded in this manner. The process can generate large amounts of metal fume, carbon dioxide, nitrogen oxides and carbon monoxide but does not involve significant amounts of UV (Ultra Violet) light so the generation of ozone is not considered significant.

Electric arc welding

Manual Metal Arc welding (MMA) or "stick" welding is the most commonly used type of electric arc welding. Other less common types of welding within this category include submerged arc and coated metal arc welding.

MMA operations involve using a consumable welding rod (also known as an electrode) which is coated with a flux. The five most common types of flux for this welding process are: Rutile (titanium dioxide), Basic (calcium carbonate and fluoride), Cellulosic (cellulose), iron powder and surfacing and non-ferrous alloy fluxes.

Upon heating, the rod decomposes and releases shielding gases for the arc. The work piece and the rod melt to form a pool of molten metal. The flux on the rod then decomposes to form gases and slag (a non metallic coating) which solidifies and is chipped off the weld upon completion of the task.

The composition and quantities of fume released during MMA welding will depend upon consumables, polarity and voltage. However it is worth considering that this type of welding is notorious for producing large amounts of fume, the composition of which will vary depending upon the rod used during the weld.

Inert arc gas welding

In this type of welding operation, a welding torch supplies a stream of inert gas (i.e. argon or helium) to the weld area. The use of an inert gas during the process generates the term MIG welding (Metal Inert Gas). This process also uses a continuous wire consumable (usually in a spool) which acts as a metal filler and assists in forming the arc.

TIG (Tungsten Inert Gas) welding is another variation of this type of category. Here the process uses a non consumable tungsten electrode and the work piece is protected by the stream of inert gas. The filler metal is introduced into the weld pool and, as there is no transfer of metal through the shielding arc, there is significantly less fume generated by this process when compared to MIG welding. These processes emit significant amounts of UV light which can lead to the formation of ozone.

Resistance welding

Resistance spot welding is the joining of two similar or dissimilar metals by passing current through the materials and interface. The heat that results from the resistance in the current path creates the weld. The use of this process allows for localised heating and bonding of metals. Although the temperatures at the weld interface are high, the short duration of the weld results in minimal dissipation of heat into surrounding materials.

The general rule of resistance welding requires that the materials must be metals. While resistance welding technology can be used to heat and bond other materials, the process of welding itself can only occur between two metals. The material must also be shaped and arranged so that the welding electrodes can apply mechanical pressure to the joint while the current pulse is applied. This ensures that the current flow during the weld follows a pre-determined path.

Soldering and brazing

Soldering operations take place at temperatures less than 427ºC and brazing operations take place at temperatures in excess of 427ºC. The pieces to be joined are heated and a filler metal (or alloy with a flux) is fed into the joining area. Soldering uses "solders" which typically contain lead or tin, or other alloys with a low melting point. Brazing alloys historically contained cadmium (which was referred to as silver solder) but are now usually cadmium free.

Soft soldering is commonly used within the electronics industry to attach components to printed circuit boards. This activity involves using a soft wire containing a flux which comprises of tin and lead (usually 40:60). The wire is usually rosin based (rosin cored solder) and is heated using an electric soldering iron.

Due to the low temperature, little metal fume is generated. However, a fume containing the decomposition of the flux material is generated which contains colophony – a well known respiratory sensitiser.

Health effects

As discussed previously, fumes produced during welding operations will vary depending upon the materials used within the welding processes, the composition of which will be carrying a mixture of airborne gases and particles which if inhaled or accidentally ingested could give rise to a significant health risk. The level of this risk will be dependant upon the composition of the fume, the concentration of the fume and the duration of the exposure.

The primary health effects associated with welding fumes are:

  • Irritation of the respiratory system – caused by gases or particles entering the throat and chest, causing coughing, tightness of the chest and breathing difficulties
  • Metal Fume Fever – inhaling metal fumes and particulates such as zinc, cadmium copper, etc can lead to flu-like symptoms, a condition known as metal fume fever. The symptoms can appear up to 12 hours after exposure and usually disappear within 24 hours of exposure. The long term and more serious implications of metal fume fever (with the exception of cadmium) are considered rare. The most common cause of metal fume fever is thought to be the welding or flame cutting of galvanised steel
  • Systemic poisoning – this can be caused by inhaling or accidentally ingesting substances which are contained within the welding fume. Such hazardous materials can include fluorides, hexavalent chromium, lead, barium and cadmium. It should be noted that not all of these substances are present within the welding fume, their presence depends upon the welding process and the materials beings welded
  • Long term, chronic effects – inhaling significant levels of welding fume are thought to lead to benign X-ray changes (often referred to as siderosis). In addition it is speculated that welders may have an increased risk of developing respiratory cancer as certain constituents of the welding fume can be carcinogenic

Further hazards

Apart from the primary hazard of inhaling welding fume, other hazards are also present in many welding operations, these can include:

Radiation

The arc can generate three types of radiation; ultra-violet, visible and infra red (heat) radiation which can be injurious in the following ways:

Ultra-violet (UV): can cause damage to skin and eyes (inflammation of the cornea and cataracts)

Visible light: dazzles eyes and impairs vision

Infra-red: damages skin and eyes

Radiation may be direct from the weld area itself or reflected from shiny or other reflective surfaces. Due to the presence of UV light in many welding operations, ozone can be generated. When combined with the high temperatures involved in many welding operations, nitrogen oxides (NOx) may be generated.

Fire and explosion

Fire is an inherent hazard associated with gas welding processes. Additionally, both flames and arcs in welding and cutting may also create a fire hazard. When fighting a fire, the appropriate fire extinguisher for the type of material must be used. Class C fires, for example those involving flammable gases such as acetylene, are best extinguished by cutting off the gas supply. Water and foam extinguishers should not be used on fires near to live electrical equipment.

There is also a danger of explosion when welding a container which previously contained explosive or flammable substances; explosive material can be trapped in grooves, seams, riveted joints or behind scale.

Noise

As a general guideline, wherever it is difficult to carry on a conversation, it is likely the noise level is unacceptable. The current Noise at Work Regulations 1989 require that when the noise reaches 85dB(A), employers should offer hearing protection to their employees. As continuous exposure for 8 hours or more to a noise level at or above 90dB(A) is injurious, hearing protection is mandatory when this level is reached. Higher levels can be tolerated for short periods but impulsive or peak noise in excess of 140 dB should not be exceeded.

As damaging noise levels can be generated from some welding processes and allied activities, welders will usually require hearing protection. For example, hand grinding may emit noise levels in the order of 108dB(A).

It should also be noted that the action levels currently defined within the current Noise at Work Regulations are to change in late 2005 / early 2006. The Control of Noise at Work Regulations 2005 will require advisory hearing protection at 80dB(A), mandatory at 85dB(A), and a 1st peak noise action level of 135dB(C). Another major change will be the introduction of a Maximum Permissible limit of 87dB(A) and 140dB(C) peak. This will prohibit anyone being subjected to a daily noise level greater than 87dB(A).

Other considerations

Degreasing solvents and coatings on the base materials can also decompose. For example, halocarbons can break down to release carbonyl chloride, hydrogen chloride and dichloroacetyl chloride. Exposure to carbonyl chloride is common and is associated with headaches and nausea.

Coatings such as PV butyral resins and polyurethane can break down to give carbon monoxide, aldehydes and acrolein.

Lethal concentrations of Nitrogen Dioxide (NO2) can also be produced during welding operations, the effects of which may not be immediate. The nitrogen dioxide produces nitric acid in the alveoli which can lead to oedema (excess fluid in the lungs).

Controlling exposure

A "suitable and sufficient" assessment of risk should be undertaken for any welding operation under the Management of Health and Safety at Work Regulations 1999 and the Control of Substances Hazardous to Health (COSHH) Regulations 2002 (as amended).

Aspects to be considered when completing the risk assessment include the welding fume generated, the risk to health arising from exposure to the fume and other risks associated with the welding process, i.e. noise, manual handling, etc.

Most gas and arc welding processes are known to create large levels of welding fume. However, the exposure of the welder and others working within the area can vary, although it is anticipated that unless adequate control measures are introduced within the workplace, the welder will be exposed to high levels of welding fume.

Exposure to welding fume can be reduced by using a combination of controls, including: elimination, substitution, control of the workplace, engineering techniques, and administrational procedures and lastly the use of personal protective equipment (PPE). Under the COSHH Regulations, a hierarchy of control measures should be adopted. This means that the use of PPE should be considered as the "last resort" and all other potential controls are not practicable.

If the welding procedure cannot be eliminated or substituted, operator work practices can be altered to reduce the welders’ exposure to fumes. This can include ensuring that welding operations where reasonably practicable are not carried out in confined spaces, or areas which are poorly ventilated. elders should adopt a working position which avoids placing their heads and upper bodies within the plume of fume generated from the welding activity. This can be achieved by either moving the work piece or adopting another position so that the welder does not form a type of enclosure with his body around the weld.

Natural ventilation (i.e. through windows and doors), mechanical ventilation (i.e. through the use of fans) and / or engineering controls (such as LEV systems) can be used to remove the fume generated from the welding operations away from the welder. To ensure that fumes generated from welding operations are effectively removed from the workplace, careful consideration should be given from the onset, preferably at the design stage of the workplace.

Where it is considered that the use of LEV systems should assist in the exposure to welding fumes, careful selection of the extraction system should be undertaken. For small scale welding operations which take place on a workbench or are held within a jig a bench top booth which is extracted from the rear or top of the booth, or an under-bench extraction system could be considered suitable.

The welding of larger work pieces which are movable could be served by a large walk-in booth with the extraction at the rear of the booth. Care should be taken to ensure that the welder is not obstructing the extraction; an ideal operator position is side on to the air flow.

When welding large immovable work pieces a point extraction system with flexible ductwork may be considered ideal for this type of work.

Effective use of LEV systems

All welders should be suitably trained with regard to the proper use of the extraction system and checks should be undertaken regularly to ensure that the systems are being used as instructed. The point of extraction (i.e. the hoods) should be positioned close to the weld, in particular no more than 1 hood / duct diameter away from the weld as this will compromise the effectiveness of the extraction. The hoods should also be positioned above the weld as this is where the plume of fume will disperse to.

Work pieces within an extraction booth should be located inside the booth.

All extraction systems should be subjected to a thorough examination and test at least once every 14 months (under the Regulation 9 of COSHH), and should be checked regularly to ensure that the system is providing an adequate air flow.

Respiratory Protective Equipment (RPE)

As mentioned above, the use of RPE is the least preferred means of control as it is the final barrier between the fume and the welder. Ideally RPE should only be used in conjunction with other control measures and careful consideration of the selection of RPE should be undertaken. The selector of RPE should take into account:

  • The composition of the fume - the RPE required may have to protect against both gases and particulates – therefore a combination of filters may have to be selected
  • "One size fits all" for many of the facepieces available to buy. The selector should take into account that people come in varying shapes and sizes, and it is important that an adequate seal is obtained between the user and the facepiece. Under the COSHH Regulations, a face fit test should be carried out to determine whether a proposed type of RPE is suitable for all individuals who are to use this as a form of protection
  • Information should also be disseminated upon the correct use, storage and maintenance of RPE

Health surveillance

The welding of stainless steel can generate the potential for both nickel and chromium VI to be present within the welding fume, and the fume of many welding operations may contain nickel. Both of these substances possess the properties which can cause occupational asthma, and nickel is also a skin sensitiser. Health surveillance may therefore be required unless the COSHH assessment deems that exposure to the welding fume is unlikely to result in occupational asthma or dermatitis. The nature of TIG welding means that little nickel or chromium VI should be present within the fume, therefore actual surveillance may not be deemed necessary. Instead a record should be kept detailing that TIG welding has been undertaken. MMA welding however can create a large amount of fume and in these circumstances may require more detailed health surveillance to take place.

Other health and safety considerations

  1. Reducing the risk of exposure to UV, infrared and visible radiation
    • Protect face and eyes using a suitable welding shield equipped with eye protection filter
    • Protect the body by wearing suitable clothing
    • Protect persons in the vicinity of the arc by means of non-reflective curtains or screens
  2. Reducing the risk of fire and explosion

    Fire

    • Remove flammable material from the welding area
    • Cover remaining flammable material with fire resistant material
    • Before welding, check that the appropriate fire fighting equipment is at hand
    • After welding, observe surrounding area of the work for an adequate period of time (suggest about one hour)

    Explosion

    • Remove explosive material by steaming or boiling out before welding. If the explosive material cannot be completely removed, fill the container with water, an inert gas or pass steam through it
  3. Welding in confined spaces

    Care should be taken to avoid a build up of toxic fumes or gases within the Confined Space. In gas-shielded welding operations, there may be a danger from asphyxiating because of oxygen deficiency. A suitably qualified person should assess the risk, determine the steps required to make the job safe and recommend precautions to be taken during the welding operation itself.

    • Ensure adequate ventilation and, if necessary, use personal protection
    • Ensure that any used vessel does not contain flammable, poisonous or explosive material
    • Ensure gas cylinders are not taken into the enclosed space
    • Check equipment for gas leaks
    • Ensure trained personnel are in attendance to deal with any emergency
    • Check by rehearsal that the worker can be rescued, should an emergency arise
    • At the end of work periods, shut off all gas supply valves and withdraw hoses and equipment
  4. Designation of hazardous areas

    It may be necessary to restrict entry to the work area to authorised persons wearing suitable protection. Warning signs may be necessary for the following hazards:

    • For welding and cutting processes, where the arc is exposed, the warning for eye protection should refer to the hazard of arc radiation
    • ‘Ear Protection Areas’ should be defined where the action levels of the Noise at Work Regulations are breeched

Published: 01st Jan 2005 in Health and Safety International

Author


Catherine Hare


an occupational hygienist with Sypol Ltd, a leading
health, safety & environmental consultancy


Catherine Hare

Website:
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