Accident Prevention Manual for Business & Industry: Engineering & Technology 13th edition National Safety Council Compiled by Dr. S.D. Allen Iske, Associate Professor University of Central Missouri

CHAPTER 22 WELDING AND CUTTING

Health Hazards Toxic metal fumes, vapors, and gases Primary pulmonary gases Nonpulmonary gases Particulate matter Pulmonary irritants and toxic inhalants Cleaning compounds Chlorinated hydrocarbons Asbestos

Health Hazards (Cont.) Most significant health hazard in welding: generation of toxic metal fumes, vapors, and gases. Exposure to various toxic gases and vapors generated during welding may produce one or more of the following: inflammation of the lungs (chemical pneumonitis) swelling and accumulation of fluids (pulmonary edema) loss of elasticity of the lungs (emphysema) chronic bronchitis asphyxiation Gases impair or injure lungs and the pulmonary system of those who inhale these hazardous substances..

Primary Pulmonary Gases These gases can impair or injure the lungs and pulmonary system of workers who inhale these gases in hazardous amounts. Ozone Oxides of nitrogen Phosgene Phosphine

Non-Pulmonary Gases These gases do not directly injure the lungs, but can cause damage by displacing oxygen in the bloodstream Carbon monoxide Carbon dioxide

Particulate Matter Benign Pneumoconisosis Aluminosis (aluminum) Anthracosis (carbon particles) Siderosis (iron oxide) Stannosis (tinoxide)

Pulmonary Irritants and Toxic Inhalants Beryllium Cadmium Chromium Copper Fluoride Lead Magnesium Manganese Mercury Molybdenum Nickel Titanium Vanadium Zinc

Safety Hazards Fire protection Drums, tanks, and closed containers Management and workers should know the safety hazards involved in the workplace. Management and workers should be trained to avoid, reduce, or eliminate safety hazards through safe work practices, PPE, and safety equipment.

Fire Protection Fire protection is very important because portable welding and cutting equipment creates special fire hazards. Work stations should be designed to provide maximum safety and fire protection Require “hot work permits”. Floors and combustible materials Hazardous locations

Drums, Tanks, and Closed Containers Thoroughly clean closed containers that held flammable liquids or other combustibles prior to welding or cutting these materials. Preference: standard cleaning procedure If not standard cleaning; two alternate methods: containers purged with inert gases fill with water to approximate area of work and vent open

Controlling Hazardous Exposures Ventilation Natural, mechanical, air cleaners Fume avoidance Avoid breathing fumes or being in path. Nonionizing radiation UV and IR affect eyes and skin from continued or repeat exposure. Noise Exposure limit Chipping Slag-chipping hammers and proper safety glasses and hearing protection

Certain materials contained in consumables, base metals, coatings, or atmospheres of welding or cutting operations have low OSHA permissible exposure limits (PELs) or have low ACGIH threshold limit values (TLVs). beryllium, arsenic, antimony, chromium, cadmium, mercury, silver, nickel, lead, copper, cobalt, manganese, selenium, vanadium, barium In welding, cutting, and associated operations, noise levels can exceed the permissible limits. Controlling Hazardous Exposures (Cont.)

Nonionizing radiation Electric arcs and gas flames produce UV and IR radiation that has a harmful effect on the eyes and skin after repeated exposures. The effects may include permanent eye injury if appropriate eye protection is not used. Bystanders and coworkers are also at risk. Controlling Hazardous Exposures (Cont.)

Personal Protective Equipment Recommendations: baseline physical chest x-ray pulmonary function testing Re-examinations by company policy or facility physician Workers trained in the type of PPE each job requires and proper use and care of equipment

Personal Protective Equipment (Cont.) Respiratory protection Regarding PELs and TLVs, if dusts, gases, and fumes cannot be kept below the applicable level, welders should wear respiratory equipment certified for the exposure (NIOSH). Certified respirators for gases, dusts, fumes or self-contained breathing apparatus for oxygen-deficient environments.

Eye protection Goggles, helmets, and shields for operators, welders, and helpers Conform to ANSI Z and Z Protective clothing Flame resistant gloves, aprons, leggings, high boots, safety shoes, and safety hats Personal Protective Equipment (Cont.)

Training in Safe Practices Management should ensure that all welders and cutters are well trained in safe practices that apply to their work. Standards for training and qualification of welders by American welding society recommended. Operators and management should recognize their joint responsibilities for safety. Management ensures welders and supervisors are trained and establishes/enforces procedures. Use only approved welding equipment.

Oxyfuel Welding and Cutting Unites metals by heating; the heat source is flame produced by the combustion of a fuel gas or gases. sometimes includes the use of pressure and a filler metal Oxygen-cutting process severs or removes metal by chemical reaction of the base metal with oxygen at an elevated temperature. Temperature is maintained by heat from the combustion of fuel gases or from an electric arc.

Oxyfuel Welding and Cutting (Cont.) Welding and cutting gases Oxygen supports combustion. Acetylene—combustion with oxygen produces higher flame temperature than any other gas used commercially. Compressed gas cylinders Pressurized cylinders—such as oxygen, hydrogen, acetylene Handling cylinders Storing cylinders—secured in upright position in a safe, dry, well- ventilated place reserved for purpose. Using cylinders Manifolds Centralized gas supply to provide continuous fuel at a rate in excess of single cylinder. Construction and design for particular gas and service for which used. Obtained and installed under supervision of reliable manufacturer.

Oxyfuel Welding and Cutting (Cont.) Distribution piping Color-coded and clearly identified by gas Specific requirements per each gas Portable outlet headers Valves and connections used for service outlet purposes Regulators Only regulators listed by UL or factory mutual used on cylinders of gas Provide uniform gas supply at correct pressure Right- or left-hand thread per gas and specific regulators for each gas

Oxyfuel Welding and Cutting (Cont.) Hoses and hose connections Oxygen and acetylene hoses are different colors or are identified/distinguished clearly Red—fuel gas Green—oxygen Black—inert gas or air hoses Torches Constructed of metal castings, forgings, and tubing Brass or bronze; may be stainless steel UL or factory mutual approved Two types: injector or pressure

Resistance Welding Resistance welding equipment is normally permanently installed so the hazards are usually minimized if the equipment has been installed properly and safe practices have been established. Hazards: lack of point-of-operation guards, flying hot metallic particles, improper handling of materials, unauthorized adjustments and repairs. Eye injuries, burns, and electrical shock.

Resistance Welding (Cont.) Resistance welding is metal-joining process from heat by resistance to flow of electric current. Parameters of resistance welding: Current magnitude, current time, and tip pressure. Each must be accurately controlled.

Resistance Welding (Cont.) Power supply Transformer secondary max 30 V and high-amp current (up to 200,000 amp) for welding Cables Abuse of the cables associated with resistance welding is severe. Demand on cables requires frequent replacement. Cables subject to pulsation, bending, and twisting leading to fatigue and breakdown Machine installation Installation conform to NEC (NFPA 70)

Arc Welding and Cutting For arc welding or cutting, two welding leads (electrode lead and work lead) are required from the source of current supply. One lead connected to work and one lead connected to electrode holder. The steel structure and connections should be capable of carrying the welding current.

Arc Welding and Cutting (Cont.) Power supply Voltages Cables Electrodes and holders Protection against electric shock Gas-tungsten arc welding, plasma arc welding, and cutting

Gas-Metal Arc Welding (GMAW) Defined as an arc-welding process that uses an arc between a continuous filler metal electrode and the weld pool. Also known as metal inert gas (MIG) process. Most of the processes uses an externally applied shielding gas or a mixture to protect the weld zone.

Flux-Cored Arc Welding Defined as an arc-welding process that uses an arc between a continuous filler metal electrode and the welding pool. Process used with shielding gas from a flux contained within the tubular electrode. Used mostly to weld steels. When used properly, the flux produces high-quality welds that have a clean, smooth appearance.

Other Welding and Cutting Processes Relatively new heat sources for welding and cutting: friction, ultrasonic, lasers. Each of these special heat sources requires guarding and safe practices. Laser (light amplification by stimulated emission of radiation)—special eye precautions