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Plasma Arc Cutting Hazards

• Mar 01, 2003

THIS is the fourth in the series of articles on welding safety. The central theme of these articles has been to emphasize that welding, if mastered and performed safely, is a rewarding profession, and that safety is an integral part of producing professional results. Previous discussions have addressed some of the safety concerns that are unique to shielded metal arc welding (SMAW), oxy-fuel welding and cutting, and general fire prevention. Please refer to previous issues for information on these topics.

By way of summary, the previous articles have presented the philosophy that welding is a profession and that the true professionals incorporate safety into all aspects of their work. Some of the hazards addressed thus far have been UV and IR light exposure, fume and particulate generation, thermal burns, occupational heat stress, exposure to electromagnetic fields, and electrocution. The effective use of eye protection is the only way to prevent injuries to the eye. Keeping one's head out of the plume of smoke is the best way to ensure respiratory safety. Protective clothing is the key to preventing thermal burns. Designing the work process to allow for adequate cool-down breaks, staying properly hydrated, and keeping fit are the best preventive measures for avoiding heat stress. Periodic testing of the equipment being used is the only way to ensure overexposure to harmful EMFs has not been reached. Keeping the equipment in good repair, working in dry environments or using adequate rubber matting, and preventing contact with the circuitry (including the work piece) are ways to prevent electrocution.

The welding processes described in this article carry the same hazards, and the injury prevention strategies are the same as for other types of welding and cutting. However, this article will address some safety concerns that are unique to plasma arc cutting (PAC), gas metal arc welding (GMAW), and gas-tungsten arc welding (GTAW), which were previously (and erroneously) known as metal-inert gas welding, or "MIG" and "TIG," respectively. Some notes on safe practices proximate to robotic welders also are provided.

Noise & Particulate Concerns
PAC is an efficient method for making high-quality cuts from stock. The process works by conveying an electric arc through some form of gas mixture (oxygen, nitrogen, argon, compressed air, etc.) through a constricted opening. This process causes the gas temperature to increase to the point where it enters the fourth state of matter--plasma. Many PAC devices employ a pilot arc to ionize the gas and initiate the transference of the electric arc, in a manner similar to that of the high-frequency starter on a gas-tungsten welder. The rush of gas traveling through the restricted opening, heated by the arc, makes the cut.

Carbon-arc cutting, a/k/a carbon-arc gouging, is often used when it becomes necessary to separate a welded joint. This process utilizes consumable carbon rods. A stream of compressed gas blows the arc for a short distance past the convergence of the carbon rods. There is some probability that plasma is generated in the carbon-arc process, but its effect is of limited consequence.

The rush of gases past the point of work in the PAC and carbon-arc gouging processes generate noise levels above 85 db-A, thus requiring the use of an effective hearing protection program. Mechanized PAC systems (and some hand-held units) may employ a water table under the platen. This will lower the noise and reduce particulate emissions. However, most CAC processes employ hand-held torches, and thus the particulate and noise levels remain high.

The GTAW process uses a tungsten alloy electrode to transmit the arc to the work piece and a shielding gas to minimize oxidation. The GTAW electrode used in stainless steel welding contains approximately 2 percent thorium--a radioactive element. Because the electrode must be occasionally ground to a fine point in order to produce the desired result, the welder may be exposed to thorium dust. The health risks associated with respirable thorium dust require the welder to take effective measures to prevent the inhalation of this dust. The two more common effective methods employ a wet grinding process and a dust collection system placed proximate to the grinding wheel. A hazardous waste is generated when thorium is ground and must be handled in accordance with environmental and occupational laws.

Much of the GTAW work is joining stainless steel. The chromium content in stainless steel and the health risks associated with overexposure to chromium make periodic air monitoring in the welder's breathing zone a standard safety measure. There are numerous strategies for preventing overexposure to chromium, and they range from the fundamental relationship of the welder to the work (keeping one's head out of the plume), to fume extraction devices, to the use of various respirators.

Spatter & Repetitive Motion Hazards
GMAW most often employs a coiled electrode (welding wire), and this allows the welder to sustain the arc for much longer periods of time. There are two hazards most commonly associated with GMAW work: overexposure to ozone, and repetitive motion injury.

The strategies for reducing exposure to ozone emissions in GMAW work are the same as those described above for GTAW. The prevention of repetitive motion injuries is best handled by employing equipment that is ergonomically friendly, avoiding working in cramped positions for prolonged periods of time, and adjusting the work/rest cycle to minimize the effects of ergonomic strain.

An expert in the GMAW process can produce some really beautiful and consistent production line welds. This perhaps makes the occurrence of weld spatter a greater concern than, for instance, welds produced by the SMAW process. The more desirable spatter prevention strategies are to more carefully match the current flow to the wire feed speed and to use better technique (feed the electrode into the weld as close to 90 degrees as possible.) Keeping the proper tension on the roller and ensuring the orifices are kept clean also influence the amount of spatter produced.

Most often, however, the welder is prone to use an aerosol anti-spatter product, and herein lies a hazard. Some anti-spatter products contain methylene chloride. The UV light, generated by the electric arc, and chlorine react to generate an extremely poisonous gas known as phosgene. Additionally, working around any chlorinated substance can produce numerous health hazards.

Each product you have in your welding shop is provided with a Material Safety Data Sheet, or MSDS. Each employee in the workplace must be familiar with the products used in that workplace. The MSDSs must be filed in a location where each employee can access them at any time during working hours. Use the information on the product label for a quick reference. Read these warnings and familiarize yourself with the associated hazards of each material you use.

Guarding & Other Issues
Robots and mechanized welders are becoming more common every day. If they are properly maintained and operated, they are capable of producing consistent results. However, one must realize machines cannot make conscious decisions and when humans get in the way of moving machinery, injuries often occur.

Therefore, those who operate and maintain these machines must constantly ensure that proper guards are in place and that other people are aware of all of the potential hazards of working close to these machines. Machines do not know--or care--whether they cause injury!

Other good practices for the professional welder include: routine monitoring to determine the levels of hazardous materials, electromagnetic fields, and noise; annual medical exams to determine the levels of workplace substances in the bloodstream and potential adverse effects on body organs; and periodically updated training on safe practices.

There is no one person who can be expected to know all aspects of any topic. Another of the identifying traits of a true professional is to realize that, sometimes, help is needed from an outside source. One source of help with safety and health issues would be to hire a full-time safety professional or seek guidance from a qualified safety and health consultant.

Another excellent source for any problem encountered in welding is the American Welding Society. The AWS is the leader in welding and its allied processes. The AWS can be reached by phoning 800-443-9353 or going online to www.aws.org. Joining AWS is the gateway to working with others in your profession.

This article originally appeared in the March 2003 issue of Occupational Health & Safety.