Transcript Slide 1

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
• Molybdenum
• Cadmium
• Nickel
• Chromium
• Titanium
• Copper
• Vanadium
• Fluoride
• Zinc
• Lead
• Magnesium
• Manganese
• Mercury
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
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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
Controlling Hazardous Exposures (Cont.)
• 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.
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.
Personal Protective Equipment (Cont.)
• Eye protection
• Goggles, helmets, and shields for operators, welders, and helpers
• Conform to ANSI Z87.1-1989 and Z89.1-1986
• Protective clothing
• Flame resistant gloves, aprons, leggings, high boots, safety shoes,
and safety hats
Training in Safe Practices
• Management should ensure that all welders and cutters
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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, wellventilated 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