Controlling Hazardous Fume and Gases During Welding

From OSHA FactSheet courtesy of Hotfoil-EHS

Welding joins materials together by melting a metal work piece along with a filler metal to form a strong joint. The welding process produces visible smoke that contains harmful metal fume and gas by-products. This article discusses welding operations, applicable OSHA standards, and suggestions for protecting welders and coworkers from exposures to the many hazardous substances in welding fume.

Types of welding

Welding is classified into two groups: fusion (heat alone) or pressure (heat and pressure) welding. There are three types of fusion welding: electric arc, gas and thermit. Electric arc welding is the most widely used type of fusion welding. It employs an electric arc to melt the base and filler metals. Arc welding types in order of decreasing fume production include:

• Flux Core Arc Welding (FCAW) filler metal electrode; flux shield
• Shielded Metal Arc (SMAW) electrode provides both flux and filler material
• Gas Metal Arc (GMAW or MIG) widely used; consumable electrode for filler metal, external gas shield
• Tungsten Inert Gas (GTAW or TIG) superior finish; non-consumable electrode; externally-supplied inert gas shield

Gas or oxy-fuel welding uses a flame from burning a gas (usually acetylene) to melt metal at a joint to be welded, and is a common method for welding iron, steel, cast iron, and copper. Thermit welding uses a chemical reaction to produce intense heat instead of using gas fuel or electric current. Pressure welding uses heat along with impact-type pressure to join the pieces.

Oxy-fuel and plasma cutting, along with brazing, are related to welding as they all involve the melting of metal and the generation of airborne metal fume. Brazing is a metal-joining process where only the filler metal is melted.

What is in welding fume?

Metals: Aluminum, Antimony, Arsenic, Beryllium, Cadmium, Chromium, Cobalt, Copper, Iron, Lead, Manganese, Molybdenum, Nickel, Silver, Tin, Titanium, Vanadium, Zinc.

Gases:

• Shielding—Argon, Helium, Nitrogen, Carbon Dioxide.
• Process—Nitric Oxide, Nitrogen Dioxide, Carbon Monoxide, Ozone, Phosgene, Hydrogen Fluoride, Carbon Dioxide.

Factors that affect worker exposure to welding fume

• Type of welding process
• Base metal and filler metals used
• Welding rod composition
• Location (outside, enclosed space)
• Welder work practices
• Air movement
• Use of ventilation controls

Health effects of breathing welding fume

• Acute exposure to welding fume and gases can result in eye, nose and throat irritation, dizziness and nausea. Workers in the area who experience these symptoms should leave the area immediately, seek fresh air and obtain medical attention.
• Prolonged exposure to welding fume may cause lung damage and various types of cancer, including lung, larynx and urinary tract.
• Health effects from certain fumes may include metal fume fever, stomach ulcers, kidney damage and nervous system damage. Prolonged exposure to manganese fume can cause Parkinson’s–like symptoms.
• Gases such as helium, argon, and carbon dioxide displace oxygen in the air and can lead to suffocation, particularly when welding in confined or enclosed spaces. Carbon monoxide gas can form, posing a serious asphyxiation hazard.

Welding and Hexavalent Chromium

• Chromium is a component in stainless steel, nonferrous alloys, chromate coatings and some welding consumables.
• Chromium is converted to its hexavalent state, Cr(VI), during the welding process.
• Cr(VI) fume is highly toxic and can damage the eyes, skin, nose, throat, and lungs and cause cancer.
• OSHA regulates worker exposure to Cr(VI) under its Chromium (VI) standard, 29 CFR 1910.1026 and 1926.1126.
• OSHA’s Permissible Exposure Limit (PEL) for Cr(VI) is 5 μg/ m3 as an 8-hour time-weighted average.

Reducing exposure to welding fume

• Welders should understand the hazards of the materials they are working with. OSHA’s Hazard Communication standard requires employers to provide information and training for workers on hazardous materials in the workplace.
• Welding surfaces should be cleaned of any coating that could potentially create toxic exposure, such as solvent residue and paint.
• Workers should position themselves to avoid breathing welding fume and gases. For example, workers should stay upwind when welding in open or outdoor environments.
• General ventilation, the natural or forced movement of fresh air, can reduce fume and gas levels in the work area. Welding outdoors or in open work spaces does not guarantee adequate ventilation. In work areas without ventilation and exhaust systems, welders should use natural drafts along with proper positioning to keep fume and gases away from themselves and other workers.
• Local exhaust ventilation systems can be used to remove fume and gases from the welder’s breathing zone. Keep fume hoods, fume extractor guns and vacuum nozzles close to the plume source to remove the maximum amount of fume and gases. Portable or flexible exhaust systems can be positioned so that fume and gases are drawn away from the welder. Keep exhaust ports away from other workers.
• Consider substituting a lower fume-generating or less toxic welding type or consumable.
• Do not weld in confined spaces without ventilation. Refer to applicable OSHA regulations (see list below).
• Respiratory protection may be required if work practices and ventilation do not reduce exposures to safe levels.

Some OSHA standards applicable to welding:

• Welding, Cutting & Brazing—29 CFR 1910, Subpart Q
• Welding & Cutting—29 CFR 1926 Subpart J
• Welding, Cutting & Heating—29 CFR 1915, Subpart D
• Permit-required confined spaces—29 CFR 1910.146
• Confined & Enclosed Spaces & Other Dangerous Atmospheres in Shipyard Employment—29 CFR 1915 Subpart B
• Hazard Communication—29 CFR 1910.1200
• Respiratory Protection—29 CFR 1910.134
• Air Contaminants—29 CFR 1910.1000 (general industry), 29 CFR 1915.1000 (shipyards), 29 CFR 1926.55 (construction)

More Information:

For more information on hexavalent chromium exposure, visit OSHA’s website at www.osha.gov.

Article reprinted here courtesy of Hotfoil-EHS.

New AFTEK-EHS Heavy Duty Air-Arc Gouging Power Supply Brochure

Air-Arc Gouging

Air arc gouging uses a generated electric arc to melt metal between the tip of a carbon electrode and the workpiece. High velocity air is shot down the electrode to blow the molten metal away, leaving a clean gouge. Gouging works on any conductive metal, including stainless steel, mild steel, copper, and aluminum. Typical applications include removal of surface and internal defects, removal of excess metal around welds, and edge preparation before welding.

Download the AFTEK-EHS Heavy Duty Air-Arc Gouging Power Supply Brochure here.

Prevent Electrostatic Precipitator and Baghouse Hopper Blockage with Hopper Heaters

Coal-fired power plants in the U.S. require the use of electrostatic precipitators or bag houses to filter out very fine fly ash particles incorporated into flow gas. The ash is collected while the flue gas passes through filter bags or large electrodes and then falls into hoppers. As the hot fly ash cools, it may condense on the hopper walls. The mixture of dry, sulfur-rich fly ash and water is very problematic, so it is very important that there is no condensation in the collection hoppers.

The mixture of water and fly ash can cause the hopper to block up (or "pluggage "), and most importantly, residual sulfur in the flue gas will combine with condensate to form sulfuric acid. The sulfuric acid attacks the inside of the hopper walls, causing corrosion, weakening walls and generating significant (and costly) maintenance problems over time.

Efficient and continuous removal of fly ash is essential for all coal-fired power plants. Collection hoppers are an integral part of the removal process. Plugging or inoperable hoppers are a known problem for engineers and maintenance crews. Constant maintenance and excess downtime seriously prevent a plant's ability to manage the production rate of fly ash. Slower fly ash production means a reduction in energy production and efficiency. The power generation of a power station is directly proportional to its rate of combustion of coal, which in turn directly affects the production of fly ash. The maintenance personnel usually attempt to remedy ash system failures in real time by disabling the affected hopper, while continually generating electricity and ash. In some situations (to prevent shutdowns of boilers), ash will be dumped on the floor, requiring costly cleaning.

Evacuation and management of fly ash is much easier if the ash is kept warm. One of the most common ways of maintaining high fly ash and hopper temperatures is by connecting electric hopper heaters to the outside hopper walls. Hopper heaters play a very important role in removing the fly ash from precipitators and bag filter walls by keeping the hopper temperatures over the flue gas acid dew point. The only function of the hopper heater is to preheat the hopper and the internal environment to prevent the formation of moisture, fly ash clumping and the development of sulphuric acid.

Hopper heaters are designed for a dirty, high-vibration power plant environment. They provide the optimum watt density for proper thermal transfer through the hopper wall and uniform heating. They are available in square, rectangular and trapezoidal shapes for any hopper design. For poke tubes, man-ways and cylindrical throats, ancillary flexible heating cloths are available. The use of electric hopper heaters in electrostatic precipitator and bag house fly ash collection systems is an effective time-tested way to prevent condensation and the resulting clumping and corrosive acids in hopper products, thus providing better opportunities for continuous production of fly ash.

Hopper, Tank & Chute Heaters plus Control Systems

Hotfoil-EHS specializes in electric surface heating systems. Applications include fly-ash hoppers on electrostatic precipitators, baghouses, coal and material handling systems, tanks, and pipes.

For more information, contact Hotfoil-EHS by calling 609.588.0900 or visit https://hotfoilehs.com.

Happy New Year from Hotfoil-EHS

Happy Holidays from Hotfoil-EHS

From all of us at Hotfoil-EHS, we wish our customers, partners and vendors a safe and happy holiday season and a wonderful 2019!

Weld Preheating Low Alloy Steels

Low alloy steels are defined as consisting of less than 10.5% Ni, Cr, Mo, and other alloy elements. In general, low alloy steels are required to be preheated to some temperature (T_PH), prior to welding. It has been suggested that T_PH for any given steel should be about 50 F above the martensite start temperature (M_S) for the particular steel being welded. Most low alloy steels, however, have fairly high M_S temperatures, making welding at or above them somewhat uncomfortable to the welder, thereby potentially compromising weld quality. For such steels, therefore, manufacturers often opt for T_PH temperatures below M_S. A case in point is AISI 4130 with an M_S of 700 F;  For this steel, federal, military, industry and company specifications typically list T_PH temperatures in the 200-600 F range, all below M_S.

Why Preheat?

Preheating drives moisture and other contaminants off the joint; moisture, lubricants and other contaminants are sources of hydrogen. More importantly, preheating serves to reduce the rate at which the metal cools down from the welding temperature to T_PH. This is so whether preheating is above or below M_S. Cooling rate reductions will lead to a general reduction in residual stress magnitudes, and also allow more time for hydrogen removal.

Most low alloy steels that may be susceptible to hydrogen-induced cracking transform from austenite during cooling through the 800-500 C (1470-930 F) temperature range. The length of time a steel spends in this range during cooling, will establish its microstructure and, hence, its susceptibility to cold cracking. To maximize cracking resistance, a microstructure that is free of untempered martensite is desired; that is, the austenite would have transformed to ferrite + carbide and no austenite will be available to transform to martensite upon reaching M_S.

For more information about preheating low alloy steels, contact Hotfoil-EHS at 609-588-0900 or by visiting their web site at https://hotfoil-ehs.com.