Welding

Don't get electrocuted by your welding machine

(article supplied by Work Cover Corporation)

They say “it’s the volts that jolts”.  But experiments prove that an electric current of only about 50 milliamps lasting for only one second can have a severe, possibly fatal, effect on the human body.  The resistance of the human body measured from hand to hand, or hand to foot is about 1,000 ohms, which means that it only takes about 50 volts differential to send 50 milliamp current across this resistance.  That is why 32 volts or less is classified as ‘extra low voltage’ in AS 3000, and a voltage between 32 and 250 volts is classified as ‘low voltage’.  

But don’t be misled into thinking that because it is called low voltage that it is relatively safe.  Voltages even as low as 50 volts for very short periods can be fatal.  And these experimental calculations assume hand to hand or hand to foot resistance.

What if the actual environmental conditions when working with electrical equipment, are much worse than those assumed in the above experiments.  Take, for example, electric arc welding.  You can often be working in a confined space and often in a cramped position.  The workspace might be hot and poorly ventilated.  You are uncomfortable and sweaty.  If you lean directly against the body of the workpiece, say, with your damp clothed shoulder, or even upper arm and your opposite hand comes into contact with the live welding electrode, you could have 80 volts from the secondary side of the welding transformer passing through your body, not dry hand to dry hand or foot, but through a shorter resistance from hand to opposite shoulder and with better contacts caused by the sweat and damp clothing.  And your heart is directly in the path.

Although manual metal arc welding (MMAW) can be performed perfectly safely, there are circumstances when there is substantial risk of electric shock.  It is obvious that poorly maintained or badly connected equipment may be extremely hazardous.  What is not so well known is that an electric shock from a welding machine can have such serious consequences.  MMAW is risky because the electrode is changed frequently while the electrode holder is electrically live. –

Many welders admit to suffering a shock if they simultaneously touch live parts of the electrode holder and the workpiece.  In most cases the consequence is only an unpleasant tingle, but sometimes the shock can lead to muscular spasms causing a fall from a height or the injury by victim striking against something.  Death by electric shock is rare, but is a real possibility.  Fuses and earth leakage devices will have no effect on reducing this hazard.

Factors which affect the severity of the shock are:

• The open circuit voltage of the welding machine, and whether the machine supplies alternating or direct current (AC is 2 to 3 times more dangerous than DC, because AC causes muscles to grip tightly).
• The pressure the victim exerts on the electrode and workpiece, because increased pressure means better contact.
• The effectiveness of insulation (gloves etc.) at the contact points, the presence of moisture from rain, perspiration or other source.
• Which parts of the body are in contact with the work and electrode, (the worst current flow path is between the left hand and torso.
• The susceptibility of the victim to shock, which is dependent on health and other factors.
• Precautions against this risk include use of properly maintained equipment, correct protective equipment and sound work practices.

To avoid electric shock –

• avoid bare skin contact with the electrode, and either
• prevent contact with the workpiece, or
• select a low voltage welding machine.

Avoiding Contact with the Electrode

Handle the electrode holder carefully.  Use dry welding gloves on both hands when handling the electrode holder or gun, particularly when changing electrodes.  Do not hold electrodes under the arm pit while changing them.  Do not wrap the electrode lead around yourself.  Remove stub ends and part used electrodes from the holder immediately welding is finished.

Ensure the electrode lead is live only while you are welding.  Do not drag live cables to the work position.  Turn off the power when welding is finished or during breaks.

Avoiding Contact with the Workpiece

Avoiding contact with the electrode is not sufficient, because an accidental brush with the electrode tip may also cause a shock.  Where possible, avoid contact with the workpiece.  Where possible, cover exposed parts of the workpiece, workbench and concrete or metallic flooring with insulation such as heat resisting blankets, rubber matting or wooden duckboards.

Wear appropriate safety clothing.  As a minimum, this should comprise heavy non-synthetic shirt and trousers or overall, rubber soled safety shoes and welding gloves.  Additional protection such as leather jacket, apron, knee pads and cap provide useful extra protection, although their brass fasteners tends to negate their electrical insulation properties.

Keep the work area, insulation and clothing dry.  In hot conditions, the risk of electrocution is increased because of clothing and equipment being soaked in perspiration.  The risk is far worse in closed environments, such as tanks or vessels, particularly when these are exposed to the sun’s heat.  Take frequent rest periods, during which time dry off equipment and clothing.  Frequently change or alternate gloves and protective clothing to avoid perspiration accumulating.  Ventilate or if possible, air condition the work area.  Ventilation will help dry perspiration and cool the body.  Cool the face with an air fed mask.  If clothing becomes saturated with perspiration, it must be changed.

Welding Machines for Electrically Hazardous Environments

If insulation of the welder from the work-piece cannot be guaranteed, the environment must be considered as electrically hazardous.  Such environments are whenever the welder has to work on or in the work-piece.  Freedom of movement is often restricted, so that the welder is forced to perform work in a cramped (kneeling, sitting or lying) position.  The hazard is compounded in wet, damp or hot locations, where humidity or perspiration considerably reduces the electrical resistance of the human body and the insulating properties of accessories.  Examples include shipbuilding work, inside vessels or pipes, in damp trenches, large steel structures and underground mines.  The hazardous environment does not need to be a confined space.

If the environment is considered electrically hazardous, then the welding equipment should have a safe voltage.  AS/NZS 3195 covers portable welding machines for both hazardous and non-hazardous environments.  The maximum OCV of direct current welding machines for both hazardous and non-hazardous environments is 113 volts.  Alternating current machines for hazardous environments should have a maximum OCV of 48volts rms instead of the normal requirement of 80 volts.  Portable welding machines for hazardous environments carry a label indicating this.

In line with international standards, there are moves to adopt similar requirements for non-portable welding machines currently covered by AS 1966.  Until such measures are adopted it is wise to measure the OCV of AC machines to determine their suitability for use in hazardous environments.  Voltage limiting safety devices are available which may be fitted to any welding machine.  Such a device automatically limits the voltage to less than 25 volts and only applies the full OCV when the electrode is struck.

This information is provided to offer guidance on a particular aspect of legislation.  It is not to be taken as a statement of law and must not be construed to waive or modify any legal obligation.