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Course 745 - Welding, Cutting, and Brazing Safety

Safety guides and audits to make your job as a safety professional easier

Operating Equipment Safely

Safety precautions when operating welding equipment vary considerably because of the different types of equipment involved. Consequently, this course discusses only general precautions pertaining to gas welding and to metal-arc welding. You can find more precautions in the technical manuals furnished by the manufacturers of the equipment.

Oxy Acetylene Instruction – Harris Welding.
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Operating Gas Welding Equipment

Follow these precautions when operating gas welding equipment:

  • Use only approved apparatus that has been examined and tested for safety.
  • Stow all cylinders carefully according to prescribed stowage procedures.
    • Stow cylinders in dry, well-ventilated, well-protected places, away from heat and combustible materials.
    • Do NOT stow oxygen cylinders in the same compartment as acetylene or other fuel gas cylinders.
    • Stow cylinders in an upright position rather than horizontally.
    • If acetylene cylinders are stowed in a non-upright position (valves at the top), do not use them until they have been allowed to stand in an upright position for at least 2 hours.
  • Do not allow anyone to tamper with cylinder safety devices.
  • When cylinders are in use, keep them far enough away from the actual welding or cutting so they will not be reached by sparks, hot slag, or flame.
  • Never place a cylinder in a position that it could form part of an electrical circuit.
  • Never interchange hoses, regulators, or other apparatus intended for oxygen with those intended for acetylene.
  • Never attempt to:
    • transfer acetylene from one cylinder to another,
    • refill an acetylene cylinder, or
    • mix any other gas with acetylene.

1. If you find an acetylene cylinder stowed in a non-upright position how long must you wait after standing the cylinder upright?

a. Over 1 hour
b. At least 2 hours
c. Up to 3 hours
d. Not more than 4 hours

Next Section

Operating Gas Welding Equipment (Continued)

xy-Acetylene Torch Cutting – Smith Equipment.
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  • Keep the valves closed on empty cylinders.
  • Do not stand in front of cylinder valves while opening them.
  • When a special wrench is required to open a cylinder valve, leave the wrench in position on the valve stem while using the cylinder so you are able to close the valve quickly in an emergency.
  • Keep oxygen cylinders and fittings away from oil and grease. Even a small amount of oil or grease may ignite violently, with explosive force, in the presence of oxygen.
  • NEVER lubricate any part of an oxygen cylinder, valve, or fitting.
  • Do not drop cylinders. Do not handle them roughly. Rough handling may cause a cylinder valve to break off, and the sudden release of gas from a full cylinder may cause it to take off like a rocket.
  • Always open cylinder valves slowly. (Do not open the acetylene cylinder valve more than 1 1/2 turns.)
  • Close cylinder valves before moving cylinders.
  • Never attempt to force unmatching or crossed threads on valve outlets, hose couplings, or torch valve inlets. The threads on oxygen regulator outlets, hose couplings, and torch valve inlets are right-handed; for acetylene, these threads are left-handed. The threads on acetylene cylinder valve outlets are right-handed but have a pitch that is different from the pitch of the threads on the oxygen cylinder valve outlets. If the threads do not match, the connections are mixed.
  • Always use the correct tip or nozzle and the correct pressure for the particular work involved. You can get this information from tables or worksheets supplied with the equipment.
  • Do not allow acetylene or acetylene and oxygen to accumulate in confined spaces. Such mixtures are highly explosive.
  • Keep a clear space between the cylinders and the work so you can reach the cylinder valves quickly and easily if necessary.
  • Open the acetylene valve first and ignite the gas while the oxygen valve is closed when lighting the torch.
  • Do not allow unburned acetylene to escape and accumulate in small or closed compartments.
  • Close the acetylene valve first and then close the oxygen valve when extinguishing the torch.
  • Secure the equipment when stopping the welding or cutting for a period of 15 minutes or more, or when the operator leaves the area.

2. What must you do if you stop welding and leave the area for more than 15 minutes?

a. Install "DO NOT Use" Tags on cylinders
b. Lay cylinders on their side
c. Inform the supervisor of actions taken
d. Secure the equipment

Next Section

Backfire and Flashback

Flashback Safety - Norco
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Unless the system is thoroughly purged of air and all connections in the system are tight before the torch is ignited, the flame is likely to bum inside the torch instead of outside the tip. The difference between the two terms backfire and flashback is this:

  • Backfire: In a backfire, there is a momentary burning back of the flame into the torch tip. A backfire is characterized by a loud snap or pop as the flame goes out. A backfire is less serious. Usually you can light the flame again without difficulty. If backfiring continues whenever the torch is lit, check for these causes:
    • overheated tip,
    • gas working pressures greater than that recommended for the tip size being used,
    • loose tip, or
    • dirt on the torch tip seat.

Flashback: In a flashback, the flame bums in or beyond the torch mixing chamber. A hissing or squealing sound usually accompanies a flashback. At the same time, the flame at the tip becomes smoky and sharp pointed. A flashback can have the same causes as a backfire. It may also indicate improper handling or something radically wrong either with the torch, such as a distorted or cracked torch head. When a flashback occurs, immediately shut off the torch oxygen valve and then close the acetylene valve. You can stop the flashback at once if you close the oxygen valve immediately.

In most instances, backfires and flashbacks result from carelessness. You can avoid these difficulties by making certain that:

  • all connections in the system are clean and tight;
  • torch valves are closed (not open or merely loosely closed) when the equipment is stowed;
  • the oxygen and acetylene working pressures used are those recommended for the torch employed; and
  • the system is purged of air before the apparatus is used.

Purging the system of air is especially necessary when you incorporate the newly connected hose and torch, or a new cylinder, into the system.

3. Which torch valve do you immediately shut off first when a flashback occurs?

a. Either the oxygen or acetylene valve
b. The oxygen valve
c. The valve causing the flashback
d. The acetylene valve

Next Section

Operating Arc Welding Equipment

What is an Arc Welding Machine – Howcast
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Before starting to work, make sure that:

  • the welding machine frame is grounded and attached firmly to the work, not merely laid loosely upon it;
  • neither terminal of the welding generator is bonded to the frame; and
  • all electrical connections are securely made.

Precautions for the operation of metal-arc welding equipment include the following:

  • use only approved welding equipment, and be sure that it is in good condition;
  • lay primary supply cable separately from portable machine cables to prevent entanglement;
  • de-energize the equipment when stopping work for any appreciable length of time;
  • completely disconnect the equipment from the source of power when it is not in use;
  • keep welding cables dry and free of oil or grease, in good condition, and protected from damage; and
  • run the cables overhead, if possible, if it is necessary to carry cables some distance from the machines. Make sure you use adequate supporting devices.

Real-Life Accident

In 2008, an employee was on an aerial lift, welding connections on beams at a building under construction. He was holding the 220V welding feeder in his right hand and removing slag with his left hand using a metal scraper. As the feeder in his right hand was feeding wire out of the tip, it curled toward his arm and contacted his jacket, which was saturated with water and sweat. The worker then received an electric shock. He was found unconscious with his arm on fire. The employee was hospitalized for treatment.

4. All of the following actions should be taken prior to arc welding operations EXCEPT _____.

a. making sure all electrical connections are secure
b. grounding the welding machine to the frame
c. making sure both terminals are bonded to the frame
d. firmly attaching the welding machine to the frame

Next Section

GTA and GMA Welding Do's and Don't's


Gas tungsten arc (GTA) welding, is also called tungsten inert gas (TIG) welding, and gas metal arc (GMA) welding. In addition to the safety precautions listed in the previous section, follow these general precautions (Do's and Don't's):


  • Do properly ventilate the welding area without excessive drafts that can affect the welding arc and shielding gas.
  • Do make sure the surface where welding is being done is dry.
  • Do make sure welding transformers or rectifiers have a power ground so that welders cannot get a shock from stray current. Voltage circuits (220-to 400-volt) can cause severe or fatal injuries.
  • Do use a welding helmet when looking at the arc. Use the correct shade of lens, usually No. 10 for GTA and No. 12 for GMA. If your eyes become irritated, see the doctor immediately.
  • Do wear suitable clothing to protect yourself from the spatter or molten particles and to shield your body from rays of the arc.
  • Do mark metal "HOT" because aluminum does not change color when heated.
  • Do make sure you fasten cylinders properly in their stations so they will not fall.
  • Do make sure to thoroughly dry the cleaned surfaces with these materials before welding.
  • Do protect hose and welding cable from being trampled or run over. Avoid tangles and kinks. Do not leave the hose and cable so they can trip people.
  • Do protect the hose, cable, and cylinders from flying sparks, hot metal, hot objects, and open flame.
  • Do make sure the connections between the regulators, adaptors, and cylinder valves are gas tight. Test them with soapy water under gas pressure.
  • Do release the pressure-adjusting screws of the regulators if you need to temporarily stop welding for an extended length of time.
  • Do close the cylinder valves and then release all gas pressure from the regulators and hose if you need to stop welding.
  • Do close the cylinder valves, make certain all gas pressures are released from the regulators and hose, and make sure the pressure-adjusting screws are turned in the counterclockwise direction prior to taking down equipment, .
  • Do use flat black paint on bulkheads and overhead of weld areas to reduce ultraviolet light reflected from GTA or GMA welding areas.

5. Why is it necessary to mark aluminum "HOT" when welding?

a. Aluminum gives off poisonous fumes
b. Marking aluminum prevents exposure
c. Aluminum does not give off heat when hot
d. Aluminum does not change color when hot

Next Section

GTA and GMA Welding Do's and Don't's (Continued)

10 Welding Safety Tips –
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  • Do not use carbon tetrachloride or other chlorinated hydrocarbons for cleaning aluminum before welding. OSHA recommends using alcohol and acetone as chemical cleaners.
  • Do not perform welding in any area where fumes from solvents are present.
  • DO not work on any wiring in an energized circuit.
  • Do not lay the torch on the work or worktable. Hang it up in a safe place so the electrode is not touching metal that may be grounded.
  • Do not change a tungsten electrode before it has cooled or while the transformer switch is in the “on” position.
  • Do not change spools of filler wire while the generator or rectifier is on.
  • Do not use defective welding cable. If a connection is operating hot, you may have a poor electrical connection.
  • Do not strike an arc on a compressed gas cylinder.
  • Do not chip or grind without safety goggles or a suitable face shield.
  • Do not move individual cylinders unless the valve protection cap, where provided, is in place and tight.
  • Do not drop or abuse cylinders in any way.
  • Do not use a hammer or wrench to open cylinder valves.
  • Do not force connections that do not fit.
  • Do not tamper with cylinder safety devices.
  • Do not expose a hose to oil or grease; these rot the rubber and cause a hazard.

6. What is the probable cause if a connection is operating hot when welding?

a. A poor electrical connection
b. The cables are not grounded
c. Too much voltage is flowing
d. The cable length is too long

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

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