SAFETY IN ARC WELDING AND CUTTING
2-12. ELECTRIC CIRCUITS
a. A shock hazard is associated with
all electrical equipment, including extension lights, electric hand
tools, and all types of electrically powered machinery. Ordinary household
voltage (115 V) is higher than the output voltage of a conventional
arc welding machine.
b. Although the ac and dc open circuit
voltages are low compared to voltages used for lighting circuits and
motor driven shop tools, these voltages can cause severe shock, particularly
in hot weather when the welder is sweating. Consequently, the precautions
listed below should always be observed.
(1) Check the welding
equipment to make certain that electrode connections and insulation
on holders and cables are in good condition.
(2) Keep hands and body insulated from
both the work and the metal electrode holder. Avoid standing on wet
floors or coming in contact with grounded surfaces.
(3) Perform all welding operations
within the rated capacity of the welding cables. Excessive heating
will impair the insulation and damage the cable leads.
Welding machine, Model 301,
AC/DC, Heliarc with inert gas attachment, NSN 3431-00-235-4728, may
cause electrical shock if not properly grounded. If one is being used,
contact Castolin Institute, 4462 York St. Denver, Colorado 80216.
c. Inspect the cables periodically for
looseness at the joints, defects due to wear, or other damage. Defective
or loose cables are a fire hazard. Defective electrode holders should
be replaced and connections to the holder should be tightened.
d. Welding generators should be located
or shielded so that dust, water, or other foreign matter will not enter
the electrical windings or the bearings.
e. Disconnect switches should be used
with all power sources so that they can be disconnected from the main
lines for maintenance.
2-13. WELDING MACHINES
a. When electric generators powered by
internal combustion engines are used inside buildings or in confined
areas, the engine exhaust must be conducted to the outside atmosphere.
b. Check the welding equipment to make
sur the electrode connections and the insulation on holders and cables
are in good condition. All checking should be done with the machine
off or unplugged. All serious trouble should be investigated by a trained
c. Motor-generator welding machines feature
complete separation of the primary power and the welding circuit since
the generator is mechanically connected to the electric rotor. A rotor-generator
type arc welding machine must have a power ground on the machine. Metal
frames and cases of motor generators must be grounded since the high
voltage from the main line does come into the case. Stray current may
cause a severe shock to the operator if he should contact the machine
and a good ground.
d. In transformer and rectifier type
welding machines, the metal frame and cases must be grounded to the
earth. The work terminal of the welding machine should not be grounded
to the earth.
e. Phases of a three-phase
power line must be accurately identified when paralleling transformer
welding machines to ensure that the machines are on the same phase and
in phase with one another. To check, connect the work leads together
and measure the voltage between the electrode holders of the two machines.
This voltage should be practically zero. If it is double the normal
open circuit voltage, it means that either the primary or secondary
connections are reversed. If the voltage is approximately 1-1/2 times
the normal open circuit voltage it means that the machines are connected
to different phases of the three phase power line. Corrections must
be made before welding begins.
f. When large weldments, like ships,
buildings, or structural parts are involved, it is normal to have the
work terminal of many welding machines connected to it. It is important
that the machines be connected to the proper phase and have the same
polarity. Check by measuring the voltage between the electrode holders
of the different machines as mentioned above. The situation can also
occur with respect to direct current power sources when they are connected
to a common weldment. If one machine is connected for straight polarity
and one for reverse polarity, the voltage between the electrode holders
will be double the normal open circuit voltage. Precautions should be
taken to see that all machines are of the same polarity when connected
to a common weldment.
g. Do not operate the polarity switch
while the machine is operating under welding current load. Consequent
arcing at the switch will damage the contact surfaces and the flash
may burn the person operating the switch.
h. Do not operate the rotary switch for
current settings while the machine is operating under welding current
load. Severe burning of the switch contact surfaces will result. Operate
the rotary switch while the machine is idling.
i. Disconnect the welding machines from
the power supply when they are left unattended.
j. The welding electrode holders must
be connected to machines with flexible cables for welding application.
Use only insulated electrode holders and cables. There can be no splices
in the electrode cable within 10 feet (3 meters) of the electrode holder.
Splices, if used in work or electrode leads, must be insulated. Wear
dry protective covering on hands and body.
k. Partially used electrodes should be
removed from the holders when not in use. A place will be provided to
hang up or lay down the holder where it will not come in contact with
persons or conducting objects.
l. The work clamp must be securely attached
to the work before the start of the welding operation.
m. Locate welding machines where they
have adequate ventilation and ventilation ports are not obstructed.
2-14. PROTECTIVE SCREENS
a. When welding is done near other personnel,
screens should be used to protect their eyes from the arc or reflected
glare. See paragraph 2-2 e for screen design and method of use.
b. In addition to using portable screens
to protect other personnel, screens should be used, when necessary,
to prevent drafts of air from interfering with the stability of the
c. Arc welding operations give off an
intense light. Snap-on light-proof screens should be used to cover the
windows of the welding truck to avoid detection when welding at night.
2-15. PLASMA ARC CUTTING AND WELDING
a. Plasma arc welding is a process in
which coalescence is produced by heating with a constricted arc between
an electrode and the work piece (transfer arc) or the electrode and
the constricting nozzle (nontransfer arc). Shielding is obtained from
the hot ionized gas issuing from the orifice which may be supplemented
by an auxiliary source of shielding gas. Shielding gas may be an inert
gas or a mixture of gases; pressure may or may not be used, and filler
metal may or may not be supplied. Plasma welding is similar in many
ways to the tungsten arc process. Therefore, the safety considerations
for plasma arc welding are the same as for gas tungsten arc welding.
b. Adequate ventilation is required during
the plasma arc welding process due to the brightness of the plasma arc,
which causes air to break down into ozone.
c. The bright arc rays also cause fumes
from the hydrochlorinated cleaning materials or decreasing agents to
break down and form phosgene gas. Cleaning operations using these materials
should be shielded from the arc rays of the plasma arc.
d. When welding with transferred arc
current up to 5A, safety glasses with side shields or other types of
eye protection with a No. 6 filter lens are recommended. Although face
protection is not normally required for this current range, its use
depends on personal preference. When welding with transferred arc currents
between 5 and 15A, a full plastic face shield is recommended in addition
to eye protection with a No. 6 filter lens. At current levels over 15A,
a standard welder's helmet with proper shade of filter plate for the
current being used is required.
e. When a pilot arc is operated continuously,
normal precautions should be used for protection against arc flash and
heat burns. Suitable clothing must be worn to protect exposed skin from
f. Welding power should be turned off
before electrodes are adjusted or replaced.
g. Adequate eye protection should be
used when observation of a high frequency discharge is required to center
h. Accessory equipment, such as wire
feeders, arc voltage heads, and oscillators should be properly grounded.
If not grounded, insulation breakdown might cause these units to become
electrically "hot" with respect to ground.
i. Adequate ventilation should be used,
particularly when welding metals with high copper, lead, zinc, or beryllium
2-16. AIR CARBON ARC CUTTING AND WELDING
a. Air carbon arc cutting is an arc cutting
process in which metals to be cut are melted by the heat of a carbon
arc and the molten metal is removed by a blast of air. The process is
widely used for back gouging, preparing joints, and removing defective
b. A high velocity air jet traveling
parallel to the carbon electrode strikes the molten metal puddle just
behind the arc and blows the molten metal out of the immediate area.
Figure 2-6 shows the operation of the process.
c. The air carbon arc cutting process
is used to cut metal and to gouqe out defective metal, to remove old
or inferior welds, for root gouging of full penetration welds, and to
prepare grooves for welding. Air carbon arc cutting is used when slightly
ragged edges are not objectionable. The area of the cut is small, and
since the metal is melted and removed quickly, the surrounding area
does not reach high temperatures. This reduces the tendency towards
distortion and cracking. The air carbon arc can be used for cutting
or gouging most of the common metals.
d. The process is not recommended for
weld preparation for stainless steel, titanium, zirconium, and other
similar metals without subsequent cleaning. This cleaning, usually by
grinding, must remove all of the surface carbonized material adjacent
to the cut. The process can be used to cut these materials for scrap
e. The circuit diagram for air carbon
arc cutting or gouging is shown by figure 2-7. Normally, conventional
welding machines with constant current are used. Constant voltage can
be used with this process.
f. When using a constant voltage (CV)
power source precautions must be taken to operate it within its rated
output of current and duty cycle.
g. Alternating current power sources
having conventional drooping characteristics can also be used for special
applications. AC type carbon electodes must be used.
h. Special heavy duty high current machines
have been made specifically for the air carbon arc process. This is
because of extremely high currents used for the large size carbon electrodes.
i. The air pressure must range from 80
to 100 psi (550 to 690 kPa). The volume of compressed air required ranges
from as low as 5.0 cu ft/min. (2.5 liter/rein.) up to 50 cu ft/min.
(24 liter/min.) for the largest-size carbon electrodes.
j. The air blast of air carbon arc welding
will cause the molten metal to travel a very long distance. Metal deflection
plates should be placed in front of the gouging operation, and all combustible
materials should be moved away from the work area. At high-current levels,
the mass of molten metal removed is quite large and will become a fire
hazard if not properly contained.
k. A high noise level is
associated with air carbon arc welding. At high currents with high air
pressure a very loud noise occurs. Ear protection, ear muffs or ear
plugs must be worn by the arc cutter.