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The Region's Only Industrial Health and Safety Magazine
The Region's Only Industrial Health and Safety Magazine
by David McKeown
Welding shops were traditionally noisy, dirty places (Figure 1). Smoke filled the air, which always had that tangy smell of ozone to it and you needed constantly to avert your eyes from blue flashes as arcs were ignited.
Periodically on a walk through any fabrication shop you would need to step carefully over trailing electrical and welding power leads, duck under protruding metalwork and dodge showers of sparks from grinding.
If your shop is reminiscent of this, read on; times and attitudes have changed. The modern workshop is a cleaner, safer place to work and is all the more efficient because of this.
There is a wide variety of welding methods available and the choice will depend on the application, the level of investment justifiable and the skill level of the workforce.
Arc welding techniques are still the most common, e.g. shielded metal arc (SMAW), gas metal arc (GMAW), submerged arc (SAW), gas tungsten arc (GTAW, Figure 2) or plasma. Arcs generate, to a greater or lesser degree, radiation spanning ultraviolet to infrared and metal evaporation that condenses to fume.
Gas welding is rarely used in production now, but oxy-fuel gas processes are still prevalent for cutting. These rely on melting and expelling metal from the plate so protection is required both to observe progress and to avoid being burned by flying metallic particles.
Resistance welding looks a relatively innocuous process as the molten metal is contained within sheets of solid material, but metal ejection can occur and injure an unwary operator.
There is increasing application of lasers in welding. These are necessarily high power and capable of inflicting serious injury at a significant distance if wrongly directed.
Welding introduces hazards but does not need to be dangerous. In the following sections, I look at each of the hazards associated with welding and its ancillary operations, comment on the level of risk for the various processes and materials and identify the precautions and any personal protective equipment (PPE) required for safe operation.
The majority of welding techniques rely on electrical power. This is usually transformed from three-phase mains (around 400V) to something appropriate for the process. Any breakdown in the insulation either before or after the welding set can expose the user to the risk of electrocution. PPE, e.g. gloves and rubber soled boots, can mitigate the damage but should not be considered a first line of defence. A schedule of regular inspection and maintenance should be in place to ensure that all wiring is to the required standard.
Arc welders work with an open circuit between the electrode and the work piece. There is therefore a risk that by mishandling – touching both the electrode and the work piece – a current path could be established through the welder’s body. Whilst the welding voltage (ca 20V) is not high, the open circuit voltage can be considerably higher (80 to100V). The risk of damaging, and possibly fatal, electrocution is real. Welders should be trained to recognise the danger and not let familiarity breed contempt. Instruct them to switch off power or place the live torch well away from the workbench before handling the work piece.
Another aspect to be considered is the return path of the current. Good, direct earth return from the work piece to the welding set is essential. It not only allows consistent parameters to be set to give optimum welding conditions for the product, but protects personnel. With an indeterminate return, the current path can track through any earthed metallic structure in the vicinity putting a wide variety of people at risk.
Welding of any material whether metallic or plastic will cause heating of the component. The article will remain hot for some time but this may not always be apparent. Severe skin burns are possible. No welded part should be handled without gloves for several minutes after completion.
There is also a significant danger of fire from sparks and ejected molten metal. Flammable material must not be stored close to a welding station. Whilst this seems an obvious requirement, it is sometimes problematic to enforce. For high quality TIG or plasma welding it is necessary to degrease the material just prior to welding. This is most usually achieved with cloth or paper soaked in a solvent. It is tempting for the operator to have a waste bin for discarding used wipes within the work area when cleaning is a repetitive requirement. The release of solvent fume within the waste bin creates a volume of highly inflammable vapour that is very prone to ignition from sparks or even hot filler stubs. Safety conscious employers should establish a degreasing station distant from the welding bay and a means of transfer of components without compromising cleanliness.
Operators should, of course, be made aware of the means of escape and the fire fighting precautions to be taken in the event of any fire.
The environment in which a welder works has a number of hazards that are not specific to the welding process itself. Manual handling of heavy awkward metal components is often required. Thinner, lighter metal sheet may have sharp edges. Slips, trips and falls may be more likely as welding often requires thick cables to be spread across the floor. Standard workshop safety and protection practice should be used to counter these problems. Welders need training in materials handling, both manual and with mechanical lifting assistance; protective gloves, helmets, overalls and boots must be worn; cabling on the floor should be minimised and clearly signed or marked as a trip hazard.
There are, in addition, hazards that are a direct result of the joining process itself. During welding, sparks and molten metal can be ejected. These are most common in arc welding but can also occur in resistance processes. In mechanised processes, guards should be used to contain the flying particles. This is not possible in manual welding so the PPE worn by the operator must be capable of protecting the body. All clothing should be fire resistant and use of leather aprons, jackets, chaps, etc is recommended.
Grinding is commonly used in preparing metal for welding and during cleaning and rectification of deposited metal. Wheel and angle grinders are favourite tools for their speed of removal of material. These, however, create a hazard, not only for the operator but for adjacent and passing personnel, as the ejected material may be thrown some distance. Obviously the operator needs adequate protection with clothing, gloves, full face shields (Figure 3) and sometimes a dust mask but the whole area also needs screening with curtains to protect others.
One of the more serious dangers is from the persistent use of vibrating hand tools: grinders, scaling hammers, pneumatic burrs, etc which can lead to long-term illness – hand-arm vibration syndrome, also known as ‘white finger’ or ‘dead hand’. Studies of the incidence of the condition have shown that action to prevent physical damage may be required when the operator has as little as 30 minutes per day use of a chipping hammer.
The most intense radiation occurs in laser welding. The beam is of sufficient power to vaporise metals it impinges upon. Clearly, if allowed to contact a human body, this beam would do severe harm. The most logical method of protection is to isolate the operator and other staff from the beam by containment of the equipment and remote operation from outside the compound.
Arcs emit radiation omni-directionally. All emit ultraviolet light to a greater or lesser extent; in GMAW welding of aluminium the emission is intense. The unprotected eye can be seriously harmed by ultraviolet light from any arc process. Arc eye or welders’ flash, an immensely uncomfortable irritation of the eye, may result from even short duration flash exposure to a welding arc. Arc eye is caused by inflammation from the action of UV radiation on the outer surface of the eyeball; long exposure could cause permanent damage.
Ultraviolet radiation also affects skin causing severe burning. Long-term exposure of the skin to UV can induce skin cancers though there is no evidence that welders are more prone than others to melanoma.
Visible light is also very strong in a welding arc. In principle this could adversely affect the retina of the eye but the human reaction is to close the eyes when submitted to intense visible light so in practice this is not an issue.
Infrared radiation is felt as heat. Welding arcs, particularly those at higher currents, will quickly burn exposed skin. The long-term effect of IR on the eye is to increase the opacity of the lens (i.e. to form cataracts) but, again, there is no evidence that welders are more prone to this than the general population. Radiation, both UV and IR, from arc welding is so pronounced that welders must use filtering to complete the task and this may ensure that they do not receive long-term exposure.
Submerged arc welding, where the arc between a continuous wire electrode and the work piece is completely covered by a bed of granulated flux which protects the arc zone, is one arc process that does not emit radiation to a harmful level. Considerable heat may be given off, but eye and skin protection can be similar to that for general workshop practice.
PPE to guard the skin against welding radiation is essential. Welders should ensure that their heads are protected by a hood. It is easy to forget that UV will penetrate even a good head of hair and cause burning of the scalp; many welders are, of course, without even that covering!
Eye protection is covered by ANSI/ASSE Z87.1-2003, Occupational and Educational Personal Eye and Face Protection Devices. The AWS Fact Sheet 31, Eye and Face Protection for Welding and Cutting Operations, is also informative.
A modern approach to filters for eye protection is to use auto-darkening lenses. Helmets with such lenses have a detector that darkens the lens to a specific grade within milliseconds of being stimulated by the presence of an arc. These are also covered by the 2003 version of ANSI Z87.1.
Work areas where welding is taking place should be screened from the surroundings by transparent tinted plastic curtains. These are defined in AWS F2.3M – 2001, Specification for the Use and Performance of Transparent Welding Curtains and Screens.
High currents in arc welding can give rise to magnetic fields larger than those experienced in other workplaces. Operators should avoid wrapping cables around themselves in order to prevent unnecessary exposure to magnetic fields, and also to avoid being pulled off balance.
Heart pacemakers may be affected by large electromagnetic fields, though the effect depends on the type of pacemaker and the medical condition it is controlling. An operator fitted with a pacemaker should discuss its use in magnetic fields with a doctor before returning to the welding workplace. It goes without saying that visitors should also be made aware of the presence of high electromagnetic radiation in the vicinity of welding to ensure their safety.
The exposure of welders’ lungs to fume is a topic deserving of a full article. It was covered in our sister publication, Health and Safety International, in July 2006 (‘Do you know your WEL?’), so the advice is not repeated here. Local and general fume extraction should be applied and individual air-fed helmets may be needed for some applications.
Another less publicised hazard is that of ingestion of toxic material. Some arc welding processes raise the temperature of materials to their boiling point. Conditions within and immediately surrounding the arc allow many chemical reactions to take place such that the fume generated may contain compounds not in the original materials. The coarsest of the particles formed condense to create deposits alongside the weld. These are usually removed by the welder to improve visual inspection of the bead. This is typically achieved with a wire brush, followed by wiping with the gloved hand. The gloves therefore become coated and, in removing them at breaks, so do the welder’s hands. If inadequate attention is given to hand washing before smoking or eating, the deposit can be ingested.
Most fluxes and metals give little cause for concern in this respect but lead, cadmium, beryllium and barium require consideration.
Soldering with lead-based solders was an issue as lead can transfer easily to the hands directly from solder. Many countries have now introduced lead-free solders with directives banning the use of lead-containing materials.
Cadmium is present in significant proportion in some silver solders. Whilst fume generation is low during soldering, there is a possibility of cadmium and cadmium oxide deposits forming beside the joint.
Beryllium is added to copper to give a strong hardening effect. Copperberyllium alloys are used for electrodes of resistance welding machines but occasionally attempts are made to weld them. Beryllium readily forms an oxide that will deposit beside the weld.
Some all-positional self shielded fluxcored wires use barium compounds to achieve good weld metal properties and positional welding capability. Deposits of barium oxide and carbonate can be formed alongside welds with these consumables.
These compounds are known toxins and in such cases, extra attention should be given to the possibility of ingestion. The responsibility is initially on the employer to understand the dangers and to minimise them. He must then inform and train the employees to take reasonable precautions with respect to personal hygiene and the frequent replacement of overalls and gloves.
Much of the gas used in welding and allied processes is supplied compressed in metal cylinders. Although several are inert or of low activity chemically, e.g. argon, helium, carbon dioxide, they pose a risk on two counts – their weight and the possibility of sudden escape of gas.
Gas cylinders are heavy, gross weights can exceed 80kg, and should be manually handled as little as possible and with great care. When sited in a store or on the shop floor, they must be held in a purpose-built stand, restrained within it by a chain. Clearly, a tall cylinder falling is a dangerous object that can inflict considerable bodily harm.
A further danger is the possibility of breaking the release valve from the neck of the cylinder yielding a sudden and violent release of gas. The force of this is sufficient to move the metal cylinder at a substantial rate. Reports claim that a full cylinder with a snapped valve can travel up to 500m and penetrate concrete block walls. Fortunately the likelihood of the valve being removed by force is small. If a cylinder topples in the workplace, it is better to let it do so than to risk personal injury by attempting to catch it. However, the severing of the release valve is not unknown; care should especially be taken if a cylinder fall could be more than a simple toppling over. Storage of cylinders on ramps and raised decks and transport by hoists and cranes with inadequate means of holding the cylinder should all be avoided.
A much greater danger exists with the use of inert gases in welding, e.g. argon, helium, nitrogen and carbon dioxide. Argon is denser than air and accumulates at the bottom of confined spaces. Welders working in confined spaces with inert gases have died of asphyxiation. Adequate forced ventilation must be provided in such spaces and the welder should be provided with breathing apparatus providing as appropriate for the task.
Some gases, notably acetylene and other fuel gases are highly flammable. When used for gas cutting or welding, the supply lines must be fitted with flashback arrestors to prevent an incorrectly set flame burning back along the line to the cylinder.
Acetylene cylinders represent a particular hazard in fire, even if the flame is not from within. Acetylene is not held as a compressed gas but is dissolved in acetone held in a porous base material. Hence it is known as Dissolved Acetylene (DA). When exposed to high temperature, DA will decompose exothermically to carbon and hydrogen. The creation of a mass of hydrogen gas and extra heat can cause an explosion. Thus when confronted with acetylene cylinders at the scene of a fire, standard Fire Service practice in some countries is to establish a 200m radius exclusion zone and to cool the cylinders for at least 24 hours.
Oxygen, whilst not flammable in its own right, greatly enhances fire as it actively supports combustion, so leakage of an oxygen cylinder caught in a fire is a serious development. Studies have shown that oxygen enrichment to only 24% (against normal air at 21%) greatly increases flame temperature and the ease with which items burn. Release of oxygen into confined space is most dangerous with the possibility of a welder’s clothing igniting with ease where there is any fire risk. Oxygen should not be used as one would use compressed air for cleaning down, operating pneumatic tools, etc.
Oxygen is highly reactive and materials that are stable in air can become ignition risks in oxygen. The UK Health and Safety Executive lists oil and grease, many synthetic rubbers and some metals as explosion risks if exposed to compressed oxygen. Great care must be taken that all equipment and additives used with oxygen are specifically approved for such contact.
All equipment used in gas processes, regulators, flashback arrestors, hoses, non-return valves and blowpipes, should be regularly inspected and maintained in accordance with manufacturers recommendations.
The key to setting up and maintaining a safe workshop is in planning and the initial stage of this is risk assessment. The employer has a responsibility to look after the health of his workforce, enforceable by law in many countries. Furthermore, there is a powerful economic advantage to getting things right at the outset rather than correcting disasters after they have happened.
Risk assessment requires only a logical approach to determining what hazards exist and what might go wrong. It is then relatively easy to decide on precautions to be taken to minimise the likelihood of the event occurring and to avoid the damage that it might do. PPE forms a significant part of the precautions, but workshop layout, scheduled equipment maintenance, staff training and insistence on good practice will all help move the welding shop from the dark ages into the modern, efficient environment that it can be today.
Help is available from www.twi.co.uk, where there are frequently asked questions and best practice guides and from TWI Training and Consultancy Services division, contact firstname.lastname@example.org.
Published: 10th May 2008 in Health and Safety Middle East
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