August 2014, Vol. 241, No. 8
Features
Workplace Air Quality In Welding, Fabrication Environment
Welding and fabrication generate lots of heat, dust and fumes that carry hazardous substances. If air quality is not controlled, these often carcinogenic and toxic substances can lead to serious illness. Obviously, suitable systems to air quality at acceptable levels are needed.
A week before Thanksgiving last year, I was waiting for a delayed flight at George Bush International in Houston, when I saw a man take a seat near my gate. At first glance he looked familiar. Though I felt I knew him, I could not place him.
It took a few minutes and a couple more glances before he walked up to me and asked me if I was Ramesh, and if he had said my name correctly. He was nearly correct, but more importantly, he turned out to be Cory Pettway, a welder I had known for 10 years. Apart from general frame of his body and voice, this was not same Cory. He appeared much more frail and weak.
We managed to switch seats and sit together for the same hour-long flight during which Cory told me he had a lung infection and thought it was due to inhaling of welding fumes. He said he was better now and traveling back to work.
I have no way to know if Cory was right about what caused his illness – possibly that is what doctors told him – but his condition led me to explore the hazards of welding fumes and dust.
Welding as a trade, if practiced with caution and care, is a perfectly safe trade and profitable. But like any other profession it has hazards that vary in different settings. Different welding cuttings and joining processes produce different types of emission which present very different classes of hazards.
Table 1 is part of a study Die Technischen Regeln für Gefahrstoffe (The Technical Rules for Hazardous Substances), conducted in Germany and published in the TRGS 528. The study explores various fabrication processes and the related emission rate of hazardous substances.
The level of hazard can be mitigated or reduced to safe levels through awareness and proper ventilation. The respiratory hazard of welding comes from the fumes and airborne particles produced by process; this is commonly known. Particles in the welding environment contain various chemicals known to damage human health. Table 2 lists some of these as well as safe operational exposure limits in mg/m3.
The terms “dust” and “fume,” for our purposes, refer to the level of dispersed particles in the air. These particles are heat generated from the materials, gases and chemicals in use. The dust and fumes, if inhaled in high concentration or in low concentration over a long time, can cause respiratory complications. If the dust and fumes contain hazardous substances, such as compounds of lead, aluminum, zinc, ozone, phosgene, nitrogen dioxide, or other carcinogenic compounds, such as nickel, chromium and cobalt, the effect on human health can be extremely harmful.
The presence of these substances in any welding environment is always possible though it varies depending on what is being welded and what type of air circulation and cleaning is available in the welding and fabrication shop.
The effectiveness of air circulation and cleaning system is limited to its ability to remove particles from the air. This ability is defined by the size of particle a system can remove from the air. The particle size and the settling time of these particles become important variables in effectiveness of the air-cleaning system. Small and lighter particles are often suspended in air by vortices and difficult to remove. Filters have been developed for both personal use and for air-cleaning systems.
In the United States, the Occupational Safety and Health Administration (OSHA) regulates workplace safety, including the air environment in construction and fabrication facilities. OSHA CFR 29, Part 1926-353 ventilation and protection in welding, cutting and heating, along with 1926-55 regulate maintenance of clean air free concerning gases, vapors, fumes, dusts and mists in construction sites.
CFR 29, Part 1926-55 limits the exposure of employees to inhalation, ingestion, skin absorption and contact with any material or substance at a concentration above those specified in the “Threshold Limit Values of Airborne Contaminants for 1970,” as specified by American Conference of Governmental Industrial Hygienists.
My search for classification and identification of respiratory filters by OSHA CFR 29 Part 1926-353 and 1926-55 did not result in specific recommendations for type of filters to use in a specific environment. In the marketplace, however, there are products from several manufacturers which filter designations. Some European regulations – especially the German Framework Regulation on Hazardous substances – have detailed guidelines on the use of specific types of filters to protect from specific sizes of particles in the air. These use an alpha-numeric numbering system like G3, G4, M5, F9, E10, U17, etc., that corresponds to specific types and sizes of airborne particles.
It is possible to group the airborne particle sizes into three groups:
• Particles measuring 1 mm to 0.1 mm (39.4 mils to 3.94 mils) that can easily be seen with the naked eye. General types of filters are available for protection from these particles.
• Particles smaller than 0.1 mm (<100 µm) (<3.94 mils) can be seen only through optical microscopes. medium classes of filters are available for these particles. • particles smaller than 0.001 mm (<1 do not settle but remain floating in the air. most oil mist and dust produced during metal processing fabrication welding fall into this category. small particles an electron microscope. very specific types filter should used to protect from international specification iso (din>
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