Welding and Cutting of Metal Using the Electric Art

WELDING AND CUTTING

OF METAL
USING THE ELECTRIC ARC











HEALTH & SAFETY UNIT

SPRING
2006

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CONTENTS
GENERAL................................................................................................... 1
ELECTRIC SHOCK PREVENTION ......................................................................... 1
ELECTRODE HOLDERS .................................................................................... 1
WELDING LEADS .......................................................................................... 1
OUTPUT TERMINALS...................................................................................... 1
ELECTRODE................................................................................................ 1
a) Equipment with on/off control (contactor) ..................................................... 1
b) Equipment with no on/off control (no contactor) .............................................. 2
BURN PREVENTION ....................................................................................... 2
NEVER USE GAS WELDING GOGGLES FOR ARC WELDING ........................................... 2
HIGH CURRENTS = STRONG MAGNETIC FIELDS ....................................................... 3
HIGH FREQUENCY INITIATION .......................................................................... 3
SAFE USE OF SHIELDING GASES......................................................................... 3
WELDING/CUTTING COATED METALS ................................................................. 3
WELDING FUMES .......................................................................................... 4
GOOD VENTILATION...................................................................................... 4
LOCAL EXTRACTION...................................................................................... 4
SURFACE CLEANING ...................................................................................... 4
CORRECT SHIELDING GAS ............................................................................... 5
WELDING TECHNIQUE.................................................................................... 5
WELDING HELMET ........................................................................................ 5

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GENERAL

Welding products and welding processes can cause serious injury or death, or
damage to other equipment or property, if the operator does not strictly observe all
safety rules and take precautionary actions.

Safe practices have developed from past experience in the use of welding and
cutting. These practices must be learned through study and training before using this
equipment. Anyone not having extensive training in welding and cutting practices
should not attempt to weld.


ELECTRIC SHOCK PREVENTION

Bare conductors, or terminals in the output circuit, or ungrounded, electrically-live
equipment can fatally shock a person. To prevent against shock, have a competent
electrician verify that the equipment is adequately grounded and learn what terminals
are electrically hot.

The body's electrical resistance is decreased when wet, permitting dangerous
currents to flow through the body. Do not work in damp areas without being
extremely careful. Stay on a dry duckboard, or rubber mat when dampness or sweat
cannot be avoided.


ELECTRODE HOLDERS

Use only fully insulated electrode holders. Do not use welding currents in excess of
the maximum rating for the holder. Never immerse the holder in water to cool it, or
lay it down on the ground or work surface. Do not touch holders connected to two
welding machines at the same time, or touch other people with the holder.


WELDING LEADS

Inspect leads often for damage to the insulation. Replace or repair cracked or worn
leads immediately. Do not loop lead around your body. Do not use welding currents
in excess of rated lead capacity, as this will lead to overheat.


OUTPUT TERMINALS

Do not touch the output terminals while the equipment is in operation. Be sure
insulating covers or protective panels are in place.


ELECTRODE

a) Equipment with on/off control (contactor)


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Welding power sources for use with gas metal arc welding (GMAW), gas tungsten
arc welding (GTAW) and similar processes normally are equipped with devices that
permit on/off control of the welding power output. When so equipped the electrode
becomes electrically HOT when the contactor is closed. Never touch the electrode
wire or any conducting object in contact with the electrode unless the contactor is
open i.e. power off.

b) Equipment with no on/off control (no contactor)

Welding power sources used with shielded metal are welding (SMAW) and similar
processes may not be equipped with welding power output on-off control devices.
With such equipment the electrode is electrically HOT when the power switch is
turned on. Never touch the electrode unless the power source is off.


BURN PREVENTION

The welding arc is very bright and hot. Sparks go everywhere, weldments are hot,
and ultraviolet and infra-red radiation is present. These arc rays penetrate
lightweight clothing and are reflected from light-coloured surfaces. The arc rays can
injure eyes permanently and burn the skin, just as in too much sunburn. Never look
at an electric arc without eye protection.

Wear protective clothing - dry gauntlet gloves designed for welding, hat, and high
backed safety shoes. Button shirt collar and pocket flaps, and wear cuffless trousers
to avoid entry of sparks and slag.

Do not wear materials of a high nylon content, i.e. shell suits. Avoid oily or greasy
clothing. A spark may ignite them.

Flammable hair preparations should not be used by persons intending to weld or cut.
Do not store petrol/gas lighters/matches in pockets whilst welding.

Wear helmet with safety goggles or glasses with side shields underneath,
appropriate filter lenses or plates (protected by clear cover glass). This is a MUST
for welding or cutting, (and chipping) to protect the eyes from radiant energy and
flying metal. Replace cover glass when broken, pitted or spattered. Always lower
the helmet before striking the arc.


NEVER USE GAS WELDING GOGGLES FOR ARC WELDING

Protect the eyes of other people in the area by use of opaque, non-reflecting and
non-flammable screens around the welding station. Do not permit anyone to view
the arc unless he/she uses the correct handshield or helmet.

Hot metal such as electrode stubs and workpieces should never be handled without
gloves. Weldments to be marked HOT on completion.





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HIGH CURRENTS = STRONG MAGNETIC FIELDS

It is well known that when an electric current flows through a conductor a magnetic
field exists around the conductor. The strength of the field is proportionate to the
current flowing. In the case of resistance spot welding, a metal object of 0.5kg can
easily be displaced 0.5m at 7KA.
Personnel who are fitted with Heart Pacemakers are advised to seek medical
clearance before using welding equipment.


HIGH FREQUENCY INITIATION

Certain welding methods, TIG/Plasma, utilise high frequency to initiate the arc. The
HF is produced from a high impedance source, therefore supplying the electrode with
a low current, high voltage. This voltage is usually sufficient to bridge air gaps of
several cm.

The effect of HF on surrounding computer equipment can be devastating.

The effect on a person receiving HF can also be quite deliberating and utmost care
should be taken when using this technique.

Alternative technique for DC TIG welding is the scratch method of arc initiation.


SAFE USE OF SHIELDING GASES

The handling of gas bottles is described in detail in the BOC guide "Safe Under
Pressure" and complimented with a HSE course on manual lifting.

All persons wishing to weld using a shielding gas in the process are required to
understand the nature of the gas they intend to use.

Each gas or gas mixture will have data and safety sheets supplied and must be
adhered to.

General consideration for shielding gases are:

a) Always insure the correct gas is being used;

b) Gas is correctly connected to the welding system;

c) Ventilation and Extraction are adequate to prevent build up of gas;

d) Correct method of shut down after weld is employed.


WELDING/CUTTING COATED METALS

Weldments - Metals containing lead, cadmium, zinc, mercury, and beryllium create
toxic fumes during welding/cutting. Severe discomfort, illness or death can result
from these fumes.

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To avoid harmful concentrations of toxic fumes, adequate local ventilation must be
used, or each person in the area as well as the operator must wear an air supplied
respirator. For beryllium, both must be used,
Metals coated with or containing materials that emit toxic fumes should not be heated
unless the coating has been removed from the work surface. The area is well
ventilated, or the operator wears an air supplied respirator.


WELDING FUMES

Welding fumes are made up of two components:

Visible Fume which appears as smoke and is effectively a multitude of small
particles, generally metal or metal oxide. This is often called the Particulate Fume.

Invisible Fume, which as the name implies, cannot be seen and is a mixture of a
number of gases. This is often called the Gaseous Fume.

Both Visible and invisible fume must be considered in any welding situation in order
to assess possible hazards.

Welding fumes tend to be unique to the welding situation, and there are general
actions which represent good welding practice and are necessary to minimise the
operators exposure to fume.


GOOD VENTILATION

Ensure good general ventilation of the whole welding area so that the atmosphere is
being continually replenished with fresh air. Remember that Argon and Carbon
Dioxide are heavier than air and gather at the bottom of containers being welded.
Concentrations of these gases can be high enough to cause risk to life through the
displacement of air.


LOCAL EXTRACTION

Local fume extraction at the side of the welding plant, rule of thumb is max distance
of extraction is equal to the diameter or the extractor opening.

Remember to exhaust to the outside of the building, well away from any air intake.


SURFACE CLEANING

Cleaning metal surfaces using chemical cleaners e.g. chlorinated hydrocarbons,
must be carried out in a separate building. All traces of the chemical from the metal
must be removed before bringing it for welding.



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CORRECT SHIELDING GAS

Always use the correct gas for the welding process. Using a gas outside its
recommendation may lead to excessive fume generation e.g. a gas for MIG dip
transfer only will fume more if used in spray mode transfer.


WELDING TECHNIQUE

The welders stance can greatly affect the level of fume in the breathing zone. Avoid
placing head in the rising plume from the weld or obscure the extractor.


WELDING HELMET

The correct design of helmet will reduce the fume levels breathed by a welder. The
helmet should be shaped to cover each side of the face, the throat and upper part of
the chest. Flat shields should be avoided.

Recommended Reading: BOC guideline "SAFE FROM WELDING FUME".


REMEMBER - Welding is a safe activity provided the correct procedures are
followed and the proper precautions taken.

Written by; Steven Wallwork, Health and Safety Technical Advisor, Materials
Technology, Faculty of Science and Engineering

References: Miller Electric Mg Co. form OM-I555A; Hobart Bros Co. Arc Welding
Systems; BOC Safe Under Pressure; BOC Safe From Welding Fume


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