New developments in advanced welding
Occupational health and safety
F. J. BLUNT, University of Cambridge, UK
The welding industry is a major player in manufacturing. It encompasses the traditional arc and gas processes as well as advanced techniques such as laser welding, friction welding and electron beam welding. More innovative use of materials leads industry to a need to find techniques to join them and the more advanced welding processes will often fulfil that role. New materials can potentially bring new hazards into the workplace.
In 1998 a group of senior managers and experts from the welding community met at a ‘Vision Workshop’ to look ahead to where the industry might be in 2020. The report of the workshop proceedings contains two items of relevance to this chapter; first, one of the strategic goals in relation to the environment was to reduce energy use by 50 % by reducing pre - and post-heating operations and through the use of lower heat input welding processes. Second, the report speaks of a vision of a workplace with improved conditions for the workforce, dispelling the image of welding as ‘dark, dirty and dangerous’.1
This chapter looks first at legislative changes relating to health and safety in Europe. Readers outside Europe may also find this section informative, since the constraints set in Europe are based on the same research data that are available to all. There is continual pressure to reduce the incidence of disease related to substances hazardous to health. Of particular interest to welders is the effect of the various constituents of fume, since many welding processes, by their nature, will always produce fume. Planned future legislation aims to reduce risks to the workforce in the areas of vibration and noise. Recent legislation in Europe has clarified the control measures that are to be expected in workplaces that have the potential to contain explosive atmospheres.
The chapter will then summarise some of the scientific research that has recently been carried out. This includes some work on explosion risks in preheating. There is some work on the measurement of fume using an improved capture method. Ongoing research aims to improve our fundamental understanding in two areas - exposure to vibration and exposure to electric and magnetic fields. Some of the environmental issues that are currently of global significance are described and their present and likely future effects on the welding industry are reviewed. The chapter ends with some sources of further information and advice. The section includes sources of legislation, the enforcement agencies and some of the key government agencies, research bodies and national and international organisations. This chapter does not give a general overview of health and safety in welding. This role is fulfilled by the book Health and Safety in Welding and Allied Processes, 5th ed.,2 which contains both an overview of and specific guidance for the major welding processes, both for readers in the UK and readers in the USA.
10.2.1 Legislative drivers in Europe
For countries within the European Community a significant amount of the law concerning industrial matters emanates from Directives that are enacted by the European Parliament and Council. Some of these Directives seek to establish freedom of trade within Europe and are concerned with setting minimum agreed standards for manufactured goods. This allows products, including machinery, to be marketed freely within Europe. Other Directives directly concern health and safety at work. They do not automatically become law in the member states, but are implemented within each state using their own legislature, to a timetable that is set by the European Parliament. Directives tend to be goal-setting rather than prescriptive. Since it takes many years for a European Directive to be enacted within member states it allows those who are to be affected by it to contribute to the consultation process and influence any decisions that are to be made in implementing it.
Many of the constituents of fume are known to have adverse effects on health. The constituents can include a wide range of metallic and non-metallic elements, oxides and other compounds. There are overall exposure limits on welding fume and there are individual exposure limits on many of the constituents of welding fume. Recently the exposure limit for manganese and its inorganic compounds (which are present in fume from manganese - containing materials) has been under review in the UK and it has now been reduced3 from an occupational exposure standard of 1mg/m3 to a workplace exposure limit of 0.5 mg/m3.
Table 10.1 summarises the UK workplace exposure limits to those substances that a welder may encounter in the workplace.
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Table 10.1 Workplace exposure limits for substances commonly found in welding and allied processes (Source: Workplace Exposure Limits3)
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In the UK the Health and Safety Executive has set a target for the reduction of occupational asthma by 30% by 2010. Occupational asthma is a term that is specifically used to describe a condition where exposure to a substance at work produces a hypersensitive state in the worker’s airways, and it triggers a subsequent reaction in them. This is a form of allergic reaction and in the worst cases can lead to a person having to change their job altogether. There are significant numbers of cases of occupational asthma reported among welders.4 While welding fume is not among the top eight agents that cause occupational asthma in the UK, nevertheless Government statistics indicate that the welding trades have the fourth highest incidence of occupational asthma.
Stainless steel is implicated in many cases of occupational asthma in welders, and it would be prudent to ensure that the local exhaust ventilation used when welding stainless steel is in excellent working order. General ventilation would not be considered adequate in controlling exposure to an asthmagen. The employer should be aware of the possibility of workers becoming sensitised and have a health surveillance programme that can identify the early symptoms. Workers should be given information about the hazards and shown how to minimise the risk to themselves. They should be told about the early warning signs, which may include coughing, wheezing and chest tightness, a runny or stuffy nose and watery or prickly eyes.
10.2.3 Work in potentially explosive atmospheres
Guidance for hot work in potentially explosive atmospheres, such as repair of petrol tanks, has been in existence for a very long while. Legislation has also been in place to lay down minimum standards for the storage and use of highly flammable liquids and liquefied petroleum gas.
As a result of the implementation of the ATEX Directive5 legislation is now in place across Europe to protect workers from dangerous substances (explosive, oxidising, extremely flammable, highly flammable or flammable) and potentially explosive atmospheres. In the UK this has been implemented as the Dangerous Substances and Explosive Atmospheres Regulations 2002.6 These repeal the former legislation relating to highly flammable liquids and specifically require employers to carry out risk assessment and implement control measures for work with dangerous substances and in potentially explosive atmospheres.
A dedicated code of practice is planned for welding operations on containers that have previously contained materials that might cause explosion. The first priority is to consider whether it is feasible to do the work using a method that does not generate heat or sparks. If hot work does prove necessary it must be carefully planned. The draft code of practice formalises the requirement for work to be done under a permit-to-work, for adequate cleaning, inspection, monitoring and control.
When planning welding in a confined space, employers should specifically consider the possibility of leaks of oxygen and the practicality of odorising the oxygen if leaks are possible. They should consider the possibility of fires and explosions due to flashback, decomposition of acetylene, and high - pressure oxygen. They should plan for the safe storage of gas and how to avoid the spread of fire to other combustible materials.
Many of the requirements that are formalised by this legislation are already considered to be good practice in the welding industry and are described in various publications.7-12 However, one aspect of the new legislation that will need careful consideration by employers is the requirement to zone areas where gases or solids that can form explosive atmospheres could be released. The process of zoning leads to a specification of what electrical equipment will be allowed in the area. Formal zoning is a new requirement and it would be expected that at the very least the gas stores should be zoned, to define the area around them that should be free from sources of ignition.
It has been known since 1911 that persistent use of certain types of vibrating tools can eventually lead to permanent damage to the hands. Early indications of damage are a numbing and blanching of the fingers and this is the origin of the name ‘vibration white finger’. If damage continues it may result in irreversible changes in the nerves, muscles, bones and joints. Welders are potentially exposed to hand-arm vibration due to their use of tools such as hand grinders, chipping hammers and needle guns.
Vibration is measured in a similar manner to noise - indeed some noise meters can also measure vibration. It is believed that the following factors are important in characterising vibration exposure that may be harmful:
• magnitude, frequency of the vibration, the total daily exposure and the pattern of exposure and rest periods;
• cumulative exposure over the worker’s lifetime;
• grip or the force that the user applies to the vibrating tool and their posture;
• area and the part of the hand that is in contact with the vibrating tool;
• type of tool and the type of workpiece;
• susceptibility of the individual, which includes such factors as smoking;
• climate.
However, even knowing these factors, it is not yet possible to predict the likelihood of vibration damage, neither is it possible to detect it in its very early stages. The National Institute for Occupational Safety and Health (NIOSH) has an informative criteria document13 that describes the condition and recommends how employers should avoid vibration-induced damage. This document does not set exposure limits, but recommends proactive measures such as medical monitoring and surveillance, engineering controls, good working practices, use of protective clothing and equipment, worker training programmes and administrative controls such as restricting the hours of use of such tools. It has a useful review of the standards and recommendations from other national organisations current at its date of publication (1989).
NIOSH is currently engaged in research projects14 to try to establish stronger links between cause and effect. They hope to use microscopy to examine the capillaries at the base of the fingernail, to see whether they can predict adverse effects from physical changes there. Using computer models of stress and strain they hope to be able to relate the way in which the soft tissues of the hand are compressed and displaced and use these as a way to predict adverse effects.
Those who already have vibration white finger are known to experience delays in the return of the warmth to their fingertips after exposure to cold. It is hoped to use infrared imaging to monitor this and use it to assess the severity of the condition. NIOSH researchers hope to instrument a chipping hammer to be able to measure the impulse at its tip simultaneously with the vibration in the handle. In this way they hope to be able to monitor the effectiveness of anti-vibration methods while being able to see whether the effectiveness of the tool remains the same. A poorly designed ‘low vibration’ tool may be less effective than its higher vibration counterparts, which in turn may lead to longer periods of use and the benefits of ‘low vibration’ may be entirely lost. Researchers will also measure the effectiveness of antivibration gloves by using an instrumented vibrating handle that can simulate various vibrating tools.
While clearly not all the characteristics of the damaging effects of vibration are known, action levels have been identified for whole-body vibration and hand-arm vibration to safeguard the health of workers. Vibration is expressed as an acceleration, in m/s2, since the degree of harm that a human suffers is related to the acceleration. The measurement is averaged over an 8 hour period, representing a nominal day’s work, and is measured as a function of frequency. This is then weighted, since the response of the body is known to be different at different vibration frequencies, the most important being in the range 5-20 Hz, and the weighted average is designated an A(8).
There is new legislation in the UK specifying maximum vibration exposure. Formerly the advisory limits on hand-arm vibration in the UK were based on the British Standard BS6842, 1987, which has now been withdrawn. This limit was 2.8m/s2 A(8), calculated from the magnitude of vibration in the dominant axis. There is a European Directive 2002/44/EC, on the subject of vibration,16 which has been implemented by Control of Vibration at Work Regulation 200515. The new legislation uses vibration measurements carried out in accordance with the new Standard BS EN ISO 5349-1, 2001,17 which calculates the vibration magnitude using measurements in three directions. Vibration magnitudes calculated in this way are larger than those obtained using the old standard by a factor of between 1 and 1.7. The new legislation defines two new exposure levels, an action level at 2.5 m/s2 A(8) and an exposure limit of 5 m/s2 A(8). It will require employers to reduce hand-arm exposure to a minimum, provide information and training, assess exposure levels, carry out a programme of measures to reduce exposure and provide appropriate health surveillance when exposure reaches the exposure action level. There is a requirement to keep exposure to below the exposure limit except under certain specified circumstances.
In the workplace, the employer can reduce the incidence of vibration - induced disease by automation and mechanisation, by purchasing low vibration tools, by reducing exposure times, by maintaining the equipment in efficient working order and by giving instruction in correct operating techniques. The workers should be educated to recognise the symptoms - that numbness or tingling after using vibrating tools may be an early warning sign and should be reported to their supervisor. Employees can help to reduce the risks by keeping warm, by avoiding smoking and by taking exercise.
Several welding, cutting and gouging processes are noisy, to the extent of exceeding the thresholds currently specified in UK and USA legislation. Examples include:
• Gouging, which can produce noise levels over 90 dB(A)
• MIG (metal inert gas) (GMAW, gas metal arc welding) welding which
can exceed 90 dB(A) • Plasma cutting, which can produce noise levels of the order of 110 dB(A).
Some processes associated with welding, such as grinding, can also produce extremely high noise levels. Our susceptibility to damage by noise, like our susceptibility to vibration, depends on frequency and the measurements are weighted to reflect the sensitivity of the human ear. Weighted measurements are denoted dB(A) in the UK, and dBA in the USA, and for simplicity dB(A) is used for the rest of this section.
Current legislation in the UK18 and USA19 (2005) require measures to be taken to protect the hearing of workers when noise levels reach 85 dB(A) averaged over an 8 hour working day, and demand protective measures to be taken to safeguard their employees’ hearing. The wearing of hearing protection becomes mandatory in the UK at a threshold of 90dB(A). Currently in some European countries the thresholds at which employers must take action are already lower than these figures.
The exposure limits currently (2005) used in the USA and UK represent thresholds at which there is a given probability of hearing damage - they are not thresholds of safety. Research has indicated20 that approximately 5% of workers exposed to 90dB(A) for an 8 hour period daily will experience a 30dB hearing loss at 1, 2 and 3 kHz after 25years, rising to almost 20% after 45 years. The corresponding figures for exposure to 85 dB(A) are approximately 2% and 10%. Therefore, even when the current exposure limits are applied, there will be a number of individuals who will experience hearing loss as a result of their work. The hearing loss that is suffered as a result of exposure to excessive noise tends to be in the frequencies that are necessary for the clear understanding of speech and the loss cannot be compensated for by a hearing aid.
The European Community has passed a Noise Directive (2003/10/EC)21 that is on a timetable for implementation in member states by 2006. When implemented, this legislation will, like previous legislation, require employers to assess noise levels where workers are likely to be exposed to risks, eliminate risks at source or reduce them to a minimum and implement appropriate health surveillance where the risk assessment indicates a risk to health. In justified circumstances weekly averaging of noise will be permitted, instead of using an 8 hour averaging period.
The most noticeable changes in the UK introduced by the Control of Noise at Work Regulations 200522 are the new exposure thresholds coming intro force in April 2006, which are significantly lower than the current figures. The new limit on personal noise exposure is 87dB(A) and 140dB (C-weighted) at the ear. Where personal exposure, not taking hearing protection into account, exceeds 85 dB(A) and 137 dB (c-weighted), there is a requirement to establish and implement a programme of technical and/or organisational measures to reduce exposure to noise. Areas where noise levels exceed 85 dB(A) and 137dB (c-weighted) will need to be marked, with access restricted where technically feasible and where the risk of exposure justifies it. This threshold also triggers mandatory use of hearing protection and appropriate health surveillance Where exposure, not taking hearing protection into account, exceeds 80dB(A) and 135 dB (c-weighted) hearing protection must be made available, information and training must be provided and audiometric testing provided where a risk to health is indicated.
