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PRINCIPLES OF WORKING SAFELY WHEN PLASMA ARC CUTTING

The following article focuses on a number of basic safety principles that can be applied to plasma arc cutting. The majority of the safety factors are generally well known, use the content of this article as a working knowledge refresher, keep safety in mind.


ELECTRICITY CAN KILL

Plasma arc cutting voltages are considerably higher than in welding processes, high enough to cause severe injury or worse! Taking the necessary safety precautions when working with plasma cutting systems is imperative. The voltage is present inside the torch between the electrode and the workpiece during the cutting process. During the cutting process, the nozzle (exposed in unshielded cutting), shield and nozzle retaining cap (in shielded cutting) prevent contact with the electrode. When you are cutting, the torch cap and nozzle will protect you from contact with the electrode.

Before inspecting or replacing torch parts, ensure that there is no power to the torch. Well-designed plasma power supplies have protective electrical circuits incorporated into their build to prevent an exposed electrode from emitting a dangerously high voltage. The circuitry is present in the torch head and works in combination with the nozzle retaining cap, as the insulated nozzle retaining cap is loosened, contact between it and the torch is broken and this isolates the power to the electrode.

Operating a plasma arc cutting system completes an electric circuit between the torch and the workpiece. The workpiece and anything touching the workpiece are part of the electrical circuit.

In the case of a mechanised cutting system, it is advisable not to touch the torch body, the workpiece, or contact the water in a water table when the plasma system is operating.

Electrical parallel circuit – with sufficiently low electrical resistance, the human body can become a part of an electrical circuit.

Avoid being a direct part of the electrical circuit – it can kill you!


VOLTAGE & CURRENT TECHNOLOGY COMPARISON

  • Plasma cutting voltages ˃ welding voltages.
  • Plasma cutting currents ˂ welding currents.
  • Plasma cutting requires voltage from 100to 200 volts.

Plasma cutting requires current from around 10 to 1000 amps.


SHOCK PREVENTION

Rule No.1:Check that the equipment is safe to use, inspect the condition of the system, look for exposed cable/lead breaks, torch damage etc. If in doubt? DO NOT USE THE SYSTEM.

Wear dry insulated gloves and boots, ensure that clothing remains dry.

Do not stand, sit, lay on, or otherwise touch any wet surface when using the plasma system.

Whilst working, the operator should be insulated from the ground by using dry insulating mats or covers big enough to prevent any physical contact with the work or ground. If there is no alternative to working in or near a damp area, exercise extreme caution.

Do not hold or pick up the workpiece, including the waste cut off, whilst cutting.

During the cutting process, leave the workpiece in place and DO NOT remove the work cable clamp.

Do not move the work clamp during the cutting process.

Prior to checking, cleaning, or changing torch consumable parts, switch off the plasma power supply or isolate the input power.

When moving a plasma power supply to a new location, ensure that it is switched off and isolated from the mains input power.

The plasma power supply cover should only be removed by a competent person, this should be done under clean and dry workshop conditions. Failure to comply could result in personal injury or worse and irreparable damage to the plasma power supply.


GROUNDING SAFETY – WORK CABLE

Ensure that there is sound metal-to-metal contact between the work cable and workpiece.

The work cable clamp should be attached to clean metal that is free of rust, dirt, paint, or other contaminants that could prevent good electrical contact.

Do not attach the work cable to the piece of material that will be severed and separated from the parent material.


EYE PROTECTION FROM PLASMA ARC RAYS

Plasma arc rays produce intense visible and invisible (ultraviolet and infrared) rays that can burn eyes and skin.

Use eye protection in accordance with applicable national and local regulations.

Wear eye protection (safety glasses or goggles with side shields, and a welding helmet) with appropriate lens shading to protect your eyes from the arc's ultraviolet and infrared rays.

PROTECTION FROM BURNS – USING PERSONAL PROTECTIVE EQUIPMENT

When plasma arc cutting, it is strongly advised that as a minimum level of personal protection against burn injury, the following is adhered to.

Wear flame-retardant clothing to cover all exposed body parts, wear a leather jacket, use leather sleeve coverings.

Overalls/Coveralls (1 piece or 2 piece Jacket and trousers) should be Cuff-less (without turn-ups) to help prevent the entry of sparks and slag.

Gauntlets, safety boots designed to prevent spark entry, welding hood and welding helmet.

Remove combustibles, such as a cigarette lighter or matches, from pockets before cutting.


EAR PROTECTION

Suitable ear protection should always be worn when operating a plasma arc cutter or working near plasma arc cutting operations.

Plasma arc cutting systems can generate noise levels in excess of 120 dB during high-amperage cutting operations, ensure that the ear protection has the correct noise protection value.

The noise lies within a frequency range of 5,000 to 20,000 Hertz; ultrasonic noise is not a hazard.


PROTECTION FROM TOXIC FUMES AND GASES

Plasma arc cutting can produce toxic fumes and gases that deplete the oxygen level in the air that we breathe, this in turn causes a reduced oxygen – blood level, leading to serious injury or worse.

Keep the cutting area well ventilated, use fume extraction systems, wear an approved air-fed respirator with the appropriate filter fitted.

Do not cut in locations near degreasing and cleaning tanks or spraying operations. The vapours from certain chlorinated solvents decompose to form phosgene gas when exposed to ultraviolet radiation.

There are conductive materials that can be cut using the plasma arc process where a considered approach is required. A number of materials and coatings contain elements that are classed as "Heavy Metals" and other toxic constituents, examples of these are: zinc (galvanized steel), lead, cadmium, chromium, beryllium etc. Such materials should not be cut without a comprehensive safety review. Operators and co-workers in close proximity are at risk, where possible the work should be done in a controlled environment. If in doubt? DON'T START CUTTING!

Never cut into canisters or containers without knowing: What were the contents? was the product toxic/explosive? has the item been thoroughly cleaned? A number of countries operate a certification system where canisters and containers are accompanied by relevant documentation that explains what can and can't be done, protect yourself and your co-workers at all times.


HAZARD - MAGNETIC FIELD 

The performance of Pacemakers and hearing aids can be seriously influenced by magnetic fields created by high current.

Pacemaker and hearing aid wearers should consult a doctor before going near any plasma arc cutting and gouging operations.

The plasma arc cutting process is no more dangerous than many other workplace practices, especially when the equipment is setup in a correct manner and safety standards are adhered to.

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