Welding and Cutting
Tools and Techniques 41-1
Welding and Cutting
41 Welding and Cutting
Welding is a method of joining metal parts together
by heating them until they melt and pressing them
Arc welding is the most common type of welding
process used in construction. Arc welding uses
intense heat to melt metal, causing the molten
metal to intermix, usually with a filler metal from
an electrode. Once the liquid metal cools, a bond is
formed, joining two pieces of metal together.
Flame cutting (i.e., oxyacetylene or oxyfuel cutting)
is an allied process that requires the use of a torch,
fuel gas, and oxygen to cut metals—primarily steel.
For some of the information in this chapter, IHSA
gratefully acknowledges its use of the Canadian
Standards Association standard CAN/CSA W117.2-12:
Safety in Welding, Cutting and Allied Processes, © CSA.
Shielded Metal Arc Welding (SMAW) is the most
common arc welding process in construction
Protective Gas from
Figure 41-1: Shielded Metal Arc Welding
SMAW uses a short length of consumable
electrode, which melts as it maintains the arc.
Melted metal from the electrode is carried across
the arc to become the filler metal of the weld.
The electrode is coated with a complex mix of
chemicals that release a shielding gas such as
carbon dioxide to keep air out of the arc zone and
protect the weld from oxidation. The composition
of the coating varies with the metal being welded.
Gas Metal Arc (GMAW) or Metal Inert Gas Welding
(MIG) uses an uncoated consumable wire that is
fed continuously down the middle of the welding
torch. A ring-like tube around the wire transports
an inert gas such as argon, helium, or carbon
dioxide from an outside source to the arc zone to
prevent oxidation of the weld (Figure 41-2).
Figure 41-2: Gas Metal Arc Welding
Flux Cored Arc Welding (FCAW) is a variation
of MIG welding. It uses a hollow consumable wire
whose core contains various chemicals that generate
shielding gases to strengthen the weld (Figure 41-3).
Figure 41-3: Flux Cored Arc Welding
Gas Tungsten Arc Welding (GTAW) or Tungsten
Inert Gas Welding (TIG) uses a non-consumable
tungsten electrode that maintains the arc and
provides enough heat to join metals (Figure 41-4).
Filler metal is added in the form of a rod held close
to the arc. The rod melts and deposits filler metal
at the weld. Shielding gases may or may not be
used, depending on the metal being welded.
Figure 41-4: Gas Tungsten Arc Welding41-2 Construction Health and Safety Manual
WELDING AND CUTTING
Oxyacetylene Welding and Cutting burns a
mixture of gases—oxygen and acetylene—to
generate heat for welding metals (Figure 41-5). It’s
the most common fuel gas cutting and welding
used in construction. The process may also employ
the use of a filler metal.
Figure 41-5: Oxyacetylene Welding
Fuel gases for welding are used alone or with oxygen.
Examples include propane, propylene, and natural gas.
Acetylene is a mixture of carbon and hydrogen. Its
stored energy is released as heat when it burns.
When burned with oxygen, acetylene can produce
a higher flame temperature (3,300°C) than any
other gas used commercially. The wide flammable
range of acetylene (2.5% to 81% in air) is greater
than that of other commonly used gases, with
consequently greater hazard.
Because each metal and metal alloy responds to
heat in a distinct way, different base metals are
used for specific purposes and applications. Below
are the common base metals used for welding.
• Mild Steel – an alloy of iron, carbon, silicon, and
occasionally molybdenum or manganese
• Stainless and High Alloy Steels – containing
iron, nickel, chromium, and occasionally cobalt,
vanadium, manganese, and molybdenum
• Aluminum – either pure or as an alloy containing
magnesium, silicon, and occasionally chromium
• Galvanized steel – steel that has been coated
with a layer of zinc to prevent corrosion.
Welders in construction are exposed to a wide
range of hazards such as inhalation of toxic fumes
and gases, serious burns from hot metal, and
electric shocks from welding cable. Eye protection
is a must for welders and others who may be
exposed to the welding process.
Physical – Ionizing radiation (x-rays, gamma rays)
– Non-ionizing radiation (ultraviolet,
– Visible light
– Temperature extremes
– Electrical energy
Chemical – Flammable/combustible products
– Welding fumes
– Toxic gases
Biological – Bacteria
Once a chemical from welding has entered the
body it may have a toxic effect. Effects can range
from mild irritation to death and are influenced by
a number of factors. Different organs may also be
affected, such as the lungs, kidneys, and brain.
The two major types of effects are acute and
chronic, as described in the Occupational Health
chapter in this manual.
Both ionizing and non-ionizing radiation may be
encountered by welders and their helpers. Ionizing
is more hazardous because it can contribute
directly to cancer.
Ionizing — A common source is the emission of
x-rays and gamma rays from equipment used to
gauge the density and thickness of pipes and to
Non-ionizing — A major source is ultraviolet,
infrared, and visible light radiation from sunlight or
Radiation produced by the welding process
is mainly non-ionizing, which includes
electromagnetic fields, infrared radiation, visible
light, and ultraviolet radiation.
Exposure to ultraviolet (UV) radiation can result
directly from the arc or from a reflection off bright
objects such as shiny metal or white clothing. It
can cause “arc eye” when sight is not adequately
protected. Eyes become watery and painful
anywhere from 2 to 24 hours after exposure. The
condition may last 1–5 days but is usually reversible
with no lasting effects. However, repeated exposure
may result in scar tissue that can impair vision.
UV exposure may also cause a temporary loss
of visual sharpness called “fluorescence.” It may
eventually lead to the development of cataracts in
the eye if eye protection is not worn.Tools and Techniques 41-3
WELDING AND CUTTING
Skin reddening, commonly known as sunburn, is
another hazard of UV exposure. Blistering may
occur in extreme cases. Although excessive
exposure to UV radiation from the sun has been
linked to skin cancer, there are no reports of
increased skin cancer rates from welding exposure.
The intensity of UV radiation varies with the type of
welding. Generally, the higher the temperature of
the welding process the higher the UV radiation.
Infrared radiation is hazardous for its thermal or
heating effects. Excessive exposure to the eye may
Visible light is released at high intensity by welding.
Short-term exposure can produce “flash blindness”
in which vision is affected by after-images and
temporary blind spots. Repeated exposure to
high-intensity visible light can produce chronic
conjunctivitis, characterized by red, tearful eyes.
X-rays and gamma rays are invisible forms of
ionizing radiation used to inspect welds during
radiographic testing. Exposure to these rays can
be extremely damaging to unprotected parts of
the body. Keep all personnel away from any area
where this type of testing is being done. X-rays are
also produced during electron beam welding. The
welding chamber must be completely shielded to
confine the x-rays and protect the operator.
Very high temperatures are caused by the welding
process. Gas flames may reach 3,300°C. Metals melt
in a range from 260°C to 2,760°C. Welded materials,
the work environment, and weather are sources of
excessive heat, which can cause muscle cramps,
dehydration, sudden collapse, and unconsciousness.
Welders may suffer frostbite and hypothermia
when working in extreme cold climates or with
welding gases stored at temperatures as low as
-268°C. Exposure to freezing temperatures can
lead to fatigue, irregular breathing, lowered blood
pressure, confusion, and loss of consciousness.
Heat stress and cold stress are both life-threatening
and, if not treated in time, can be fatal.
Sound waves over 85 dBA emitted at high intensity
by welding equipment can lead to hearing loss.
Noise has also been linked to headaches, stress,
increased blood pressure, nervousness, and
excitability. (See Chapter 14: Hearing Protection for
information on maximum exposures for workers
not equipped with hearing protection.)
Welding noise is produced by the power source, the
welding process, and by secondary activities such as
grinding and hammering. Gasoline power sources may
lead to sound exposures over 95 dBA. Arc gouging
may produce sound levels over 110 dBA. Grinding,
machining, polishing, hammering, and slag removal all
contribute to high levels of noise. Substantial hearing
loss has been observed in welders.
Electrical shock is the effect produced by current
on the nervous system as it passes through the
body. Electrical shock may cause violent muscular
contractions, leading to falls and injuries. It may
also have fatal effects on the heart and lungs.
Electrical shock may occur as a result of improper
grounding and/or contact with current through damp
clothing, wet floors, and other humid conditions. Even
if the shock itself is not fatal, the jolt may still cause
welders to fall from their work positions.
Electrical burns are an additional hazard. The burns
often occur below the skin surface and can damage
muscle and nerve tissue. In severe cases, the results
can be fatal.
The extent of injury due to electrical shock depends
on voltage and the body’s resistance to the current
passing through it (see the Electrical Hazards
chapter in this manual). Even low voltages used
in arc welding can be dangerous under damp or
humid conditions. Welders should keep clothing,
gloves, and boots dry and stay well insulated from
work surfaces, the electrode, the electrode holder,
and grounded surfaces.
Stray welding current may cause extensive
damage to equipment, buildings, and electrical
circuits under certain conditions.
Chlorinated solvents for degreasing, zinc chromatebased paint for anti-corrosion coatings, cadmium or
chromium dusts from grinding, and welding fumes
are all classified as chemical hazards.
Arc welders are at particular risk since the high
temperatures generated by the arc can release heavy
concentrations of airborne contaminants.
Chemical hazards may injure welders through
inhalation, skin absorption, ingestion, or injection into
the body. Damage to respiratory, digestive, nervous,
and reproductive systems may result. Symptoms of
overexposure to chemicals may include nosebleeds,
headaches, nausea, fainting, and dizziness.
Read the manufacturer’s safety data sheet (SDS) for
information on protective measures for any chemical
you encounter in the workplace.
The most common chemical hazards from welding
are airborne contaminants that can be subdivided
into the following groups:
2. Gases and Vapours
The amount and type of air contamination from
these sources depends on the welding process, the
base metal, and the shielding gas. Toxicity depends
on the concentration of the contaminants and the
physiological response of individual workers.41-4 Construction Health and Safety Manual
WELDING AND CUTTING
Some of the metal melted at high temperates
during welding vaporizes. The metal vapour then
oxidizes to form a metal oxide. When this vapour
cools, suspended solid particles called fume
particles are produced. Welding fumes consist
primarily of suspended metal particles invisible to
the naked eye.
Metal fumes are the most common and the most
serious health hazard to welders. Fume particles
may reach deep into the lungs and cause damage
to lung tissue or enter the bloodstream and travel
to other parts of the body. The following are some
common welding fumes.
Beryllium is a hardening agent found in copper,
magnesium, and aluminum alloys. Overexposure
may cause metal fume fever. Lasting for 18–24
hours, the symptoms include fever, chills,
coughing, dryness of mouth and throat, muscular
pains, weakness, fatigue, nausea, vomiting, and
headaches. Metal fume fever usually occurs
several hours after the exposure and the signs
and symptoms usually abate 12–24 hours after
the exposure with complete recovery. Immunity
is quickly acquired if exposure occurs daily, but
is quickly lost during weekends and holidays. For
this reason, metal fume fever is sometimes called
“Monday morning sickness.”
Long-term (chronic) exposure to beryllium fumes
can result in respiratory disease. Symptoms may
include coughing and shortness of breath. Beryllium
is a suspected carcinogen—that is, it may cause
cancer in human tissue. It is highly toxic. Prolonged
exposure can be fatal.
Cadmium coatings can produce a high
concentration of cadmium oxide fumes during
welding. Cadmium-plated or cadmium-containing
parts resemble, and are often mistaken for,
galvanized metal. Cadmium is also found in solders
(especially silver solder) and brazes.
Overexposure to cadmium can cause metal fume
fever. Symptoms include respiratory irritation,
a sore, dry throat, and a metallic taste followed
by cough, chest pain, and difficulty in breathing.
Overexposure may also make fluid accumulate
in the lungs (pulmonary edema) and may cause
death. The liver, kidneys, and bone marrow can also
be injured by the presence of this metal.
Chromium is found in many steel alloys. Known to
be a skin sensitizer, it may cause skin rashes and
skin ulcers with repeated exposure. Chromium also
irritates mucous membranes in areas such as eyes
and nose and may cause perforation of the nasal
septa. Inhaled chromium may cause edema and
Lead can be found in lead-based paints and some
metal alloys. Lead poisoning results from inhalation
of lead fumes from these lead-based materials.
The welding and cutting of lead or lead-coated
materials is the primary source of lead poisoning for
welders. Symptoms include loss of appetite, anemia,
abdominal pains, and kidney and nerve damage.
Under Ontario law, lead is a designated substance
requiring special precautions for use and handling.
Nickel is found in many steel alloys including
stainless steel and monel. It is a sensitizing agent
and in certain forms is toxic and carcinogenic.
Nickel fumes can also produce cyanosis, delirium,
and death 4 to 11 days after exposure.
Zinc is found in aluminum and magnesium alloys,
brass, corrosion-resistant coatings such as
galvanized metal, and brazing alloys. Inhaling zinc
fumes during the cutting or welding of these metals
may cause metal fume fever.
Gases and Vapours
A gas is a low-density chemical compound that
normally fills the space in which it is released. It
has no physical shape or form. Vapour is a gas
produced by evaporation.
Several hazardous vapours and gases may be
produced by welding. Ultraviolet radiation, surface
coatings, shielding gases, and rod coatings
are primary sources of vapours and gases.
Overexposure may produce one or more of the
following respiratory effects:
• Inflammation of the lungs
• Pulmonary edema (fluid accumulation in the
• Emphysema (loss of elasticity in lung tissue)
• Chronic bronchitis
Hydrogen fluoride (HF) gas can be released by
the decomposition of rod coatings during welding
and irritates the eyes and respiratory system.
Overexposure can injure lungs, kidney, liver, and
bones. Continued low-level exposures can result in
chronic irritation of nose, throat, and bronchial tubes.
Nitrogen oxide (NOx) gas is released through a
reaction of nitrogen and oxygen promoted by high
heat and/or UV radiation. It is severely irritating
to the mucous membranes and the eyes. High
concentrations may produce coughing and chest
pain. Accumulation of fluid in the lungs can occur
several hours after exposure and may be fatal.
Ozone gas is formed by the reaction of oxygen in
air with the ultraviolet radiation from the welding
arc. It may be a problem during gas-shielded metal
arc welding in confined areas with poor ventilation.
Overexposure can result in an accumulation of fluid
in the lungs (pulmonary edema) which may be fatal.Tools and Techniques 41-5
WELDING AND CUTTING
Phosgene gas is formed by the heating of
chlorinated hydrocarbon degreasing agents. It
is a severe lung irritant and overexposure may
cause excess fluid in the lungs. Death may result
from cardiac or respiratory arrest. The onset of
symptoms may be delayed for up to 72 hours.
Phosphine or hydrogen phosphide is produced
when steel with a phosphate rustproofing coating
is welded. High concentrations irritate eyes, nose,
Asphyxiants are chemicals that interfere with the
body’s ability to transfer oxygen to the tissues.
The exposed individual suffocates because the
bloodstream cannot supply enough oxygen for life.
There are two main classes of asphyxiants:
1. Simple asphyxiants displace oxygen in air,
thereby leaving little or none for breathing. In
welding, simple asphyxiants include commonly
used fuel and shielding gases such as acetylene,
hydrogen, propane, argon, helium, and carbon
dioxide. When the normal oxygen level of
21% drops to 16%, breathing as well as other
problems begin, such as lightheadedness,
buzzing in the ears, and rapid heartbeat.
2. Chemical asphyxiants interfere with the body’s
ability to transport or use oxygen. Chemical
asphyxiants can be produced by the flamecutting of metal surfaces coated, for instance,
with rust inhibitors. Hydrogen cyanide, hydrogen
sulphide, and carbon monoxide are examples of
chemical asphyxiants—all highly toxic.
Dusts are fine particles of a solid that can remain
suspended in air and are less than 10 micrometres
in size. This means they can reach the lungs. Dusts
may be produced by fluxes and rod coatings,
which release phosphates, silicates, and silica.
The most hazardous of these is silica which can
produce silicosis—a disease of the lung which causes
shortness of breath and can shorten life expectancy.
Biological hazards are a relatively minor concern
for construction welders. However, exposure to
bacteria may occur in sewer work, while air handling
systems contaminated by bacteria and fungi can
cause legionnaires’ disease and other conditions.
A fungus that grows on bird or bat droppings is
responsible for a disease called histoplasmosis,
producing flu-like symptoms. Contact may occur
where buildings contaminated with droppings are
being renovated or demolished.
There is always a threat of fire with welding. Fires
may result from chemicals reacting with one
another to form explosive or flammable mixtures.
Many chemicals by themselves have low ignition
points and are subject to burning or exploding if
exposed to the heat, sparks, slag, or flame common
in welding. Even sparks from cutting and grinding
may be hot enough to cause a fire.
In welding, oxygen and acetylene present the
most common hazards of fire and explosion. Pure
oxygen will not burn or explode but supports the
combustion of other materials, causing them to
burn much more rapidly than they would in air.
Never use oxygen to blow dust off your clothing.
Oxygen will form an explosive mixture with
acetylene, hydrogen, and other combustible gases.
Acetylene cylinders are filled with a porous material
soaked with acetone, the solvent for acetylene.
Because acetylene is highly soluble in acetone at
cylinder pressure, large quantities can be stored
in comparatively small cylinders at relatively low
pressures. When exposed to high temperature,
excess pressure, or mechanical shock, acetylene
gas can undergo an explosive decomposition
reaction. In addition, if this reaction or an ignition
of acetylene occurs within the torch base or supply
hose, it can circulate back into the storage cylinder,
causing it to explode.
Welding hazards must be recognized, evaluated, and
controlled to prevent injury to personnel and damage
to property. The WHMIS chapter in this manual
explains the information on hazardous materials that
can be provided by WHMIS symbols, labels, and
safety data sheets. Once a welding hazard has been
identified, controls can be implemented at its source,
along its path, or at the worker.
Types and effects of airborne contaminants
produced by welding depend on the working
environment, the kind of welding being done, the
material being welded, and the welder’s posture
and welding technique.
The environment for welding is a very important
factor in the degree of exposure to fumes, vapours,
and gases. Welding is best done outside or in open
areas with moderate air movement. Air movement
is necessary to dissipate fumes before they reach
the welder. Enclosed areas with little ventilation
can lead to very high exposure levels because the
contaminant is not dispersed. In confined spaces,
fume, vapour, and gas levels that are dangerous to
life and health may result. Welding may also use up
the oxygen in a confined space, causing the welder
to lose unconsciousness or even die.41-6 Construction Health and Safety Manual
WELDING AND CUTTING
The base metal to be welded is an important factor
in the production of fumes, vapours, and gases. The
base metal will vaporize and contribute to the fume.
Coatings such as rust inhibitors have been known to
cause increased fume levels which may contain toxic
metals. All paints and coatings should be removed
from areas to be welded as they can contribute to
the amount and toxicity of the welding fume.
Welding rod is responsible for up to 95% of the
fume. Rods with the fewest toxic substances can’t
always be used because the chemistry of the rod
must closely match that of the base metal.
Shielding gas used during SMAW can effect the
contaminants produced. Using a mixture of argon and
carbon dioxide instead of straight carbon dioxide has
been found to reduce fume generation by up to 25%.
Nitric oxide in the shielding gas for aluminum during
GMAW has been found to reduce ozone levels.
Welding process variables can have a big effect
on the fume levels produced. Generally, fume
concentrations increase with higher current, larger
rods, and longer arc length. Arc length should
be kept as short as possible while still producing
good welds. Polarity is also a factor. Welding with
reverse polarity (workpiece negative) will result in
higher fumes than welding with straight polarity
The welder’s posture and technique are crucial
factors in influencing exposure. Studies have
shown that different welders performing the exact
same task can have radically different exposures.
Welders who bend over close to the welding
location, those who position themselves in the
smoke fume, and those who use a longer arc than
required will have a much greater exposure. The
welder should try to take advantage of existing
ventilation (cross drafts, natural, or mechanical) to
direct the fume away from the breathing zone.
Ventilation is required for all cutting, welding, and
brazing. Adequate ventilation is defined as the use
of air movement to
• Reduce concentrations of airborne contaminants
below the acceptable limits in the worker’s
breathing zone and the work area
• Prevent the accumulation of combustible gases
and vapours, and
• Prevent oxygen-deficient or oxygen-enriched
You need to take special steps to provide
ventilation in the following locations.
• Spaces with less than 283 cubic metres per welder
• Rooms with a ceiling lower than 4.9 metres
• Confined spaces or where the area contains
partitions or other structures that significantly
Natural dilution ventilation — The majority of
construction projects depend on natural dilution
ventilation (i.e., welding outside in a light breeze or
inside with doors and windows open). When using
natural dilution ventilation, you must make sure to
“keep your head out of the fume” (Figure 41-6).
NOTE: Welder must stay
to one side of fume.
Figure 41-6: Natural Dilution Ventilation
Mechanical dilution ventilation is common in most
welding shops. Fans such as roof exhaust fans
and wall fans force outside air into and out of the
building. General mechanical ventilation in most
cases will deflect the fume out of the welder’s
breathing zone (Figure 41-7). Welders need
different amounts of fresh-air ventilation depending
on the specific task and the size of rod they’re
using. For air volume recommendations, see the
American Conference of Governmental Industrial
Hygienists’ Industrial Ventilation: A Manual of
Figure 41-7: Mechanical Dilution Ventilation
Local exhaust ventilation consists of an exhaust
fan, air cleaner, and ducted system dedicated to
removing airborne contaminants at the source and
exhausting them outdoors. Local exhaust ventilation
is preferred over dilution ventilation because it is
better able to prevent airborne contaminants from
entering the welder’s breathing zone.
Local exhaust ventilation is recommended for
welding where toxic airborne contaminants are
produced and/or where a high rate of fume is
produced—for instance, during GMAW in confined
areas with little ventilation where the shielding
gases can build up to toxic levels.Tools and Techniques 41-7
WELDING AND CUTTING
There are three types of local exhaust ventilation
systems for welding:
1) Portable fume extractor with flexible ducting
2) Fume extraction gun (Figure 41-9)
3) Welding bench with portable or fixed hood
Figure 41-8: Portable Fume Extractor
Figure 41-9: Fume Extraction Gun
Figure 41-10: Bench with Portable Hood
The effectiveness of local exhaust ventilation
depends on the distance of the hood from
the source, air velocity and volume, and hood
placement. Hoods should be located close to the
source of airborne contaminants. The hood is
placed above and to the side of the arc to capture
Warning: In all processes that use shielding gas,
air velocities in excess of 30 metres/minute may
strip away shielding gas.
There are two methods for determining ventilation
requirements. One uses air sampling to measure
the welder’s exposure to airborne contaminants
and to determine the effectiveness of the
ventilation provided. Monitoring is not well suited to
construction because site conditions are constantly
The other method uses tables to select the type
of ventilation according to the process, materials,
production level, and degree of confinement used
in the welding operation.
Ventilation guidelines for different welding
processes are spelled out in Canadian Standards
Association standard CAN/CSA W117.2-12: Safety in
Welding, Cutting and Allied Processes, © CSA.
An isolation chamber is a metal box with built-in
sleeves and gloves. The work is welded inside the
box and viewed through a window. This method is
used to weld metals that produce extremely toxic
fumes. The fumes are extracted from the isolation
chamber and ducted outdoors.
Respiratory protection will not be required for
most welding operations if adequate ventilation
is provided. However, when ventilation or other
measures are not adequate, or when the welding
process creates toxic fumes (as with stainless steel
and beryllium), respiratory protection must be worn.
Select respiratory protection based on estimated
exposure and the toxicity of the materials.
Disposable fume respirators are adequate for low
fume levels and relatively non-toxic fumes. For
higher exposures or for work involving toxic fumes,
a half-mask respirator with cartridges suitable for
welding fume should be used (Figure 41-11).
Figure 41-11: Half-Mask Respirator
In areas where fume or gas concentrations may be
immediately dangerous to life and health, a selfcontained breathing apparatus (SCBA) or a suppliedair respirator with a reserve cylinder should be used.
Use only supplied air or self-contained respirators in
areas where gases may build up or where there can
be a reduction in oxygen.41-8 Construction Health and Safety Manual
WELDING AND CUTTING
A welder required to wear a respirator must
be instructed in its proper fitting, use, and
maintenance. For more information, refer to
Chapter 15: Respiratory Protection in this manual.
Sparks and slag from cutting, grinding, and welding
can travel great distances and disappear through
cracks in walls and floors or into ducts. They
may contact flammable materials or electrical
equipment. Fires have started in smoldering
materials that went undetected for several hours
after work was done.
Take the following steps to prevent fires and
• Obtain a hot work permit through the safety
officer if required.
• Keep welding area free of flammable and
• Use a flammable gas and oxygen detector to
determine whether a hazardous atmosphere
• Provide fire barriers such as metal sheets or fire
blankets and fill cracks or crevices in floors to
prevent sparks and slag from passing through.
• Provide fire extinguishers suitable for potential
types of fire. Know where the extinguishers are
and how to use them.
• Provide a firewatch where necessary—a worker
to watch for fires as the welder works and for at
least thirty minutes afterward. The person must
be fully trained in the location of fire alarms
and the use of fire-fighting equipment. Some
situations may require more than one firewatch,
such as on both sides of a wall or on more than
Cutting torches should be equipped with
reverse flow check valves and flame arrestors to
prevent flashback and explosion (Figure 41-12).
These valves must be installed according to the
Reverse Flow Condition Check Valve
Normal Flow Condition Check Valve
Figure 41-12: Reverse Flow Check Valves
Drums, tanks, and closed containers that have held
flammable or combustible materials should be
thoroughly cleaned before welding or cutting. As
an added precaution, purge with an inert gas such
as nitrogen or carbon dioxide and fill with water to
within an inch or two of the place to be welded or
cut and vent to atmosphere (Figure 41-13).
Joint to be repaired
Keep air space as
small as possible
Figure 41-13: Fill Tanks that Previously Contained
Flammable Material with Water
Many containers that have held flammable or
combustible materials present special problems.
Consult the manufacturer or the product SDS for
Arc Welding and Cutting
Use only manual electrode holders that are
specifically designed for arc welding and cutting
and can safely handle the maximum-rated current
capacity required by the electrodes.
Any current-carrying parts passing through the
portion of the holder in the welder or cutter’s hand,
and the outer surfaces of the jaws of the holder,
should be fully insulated against the maximum
voltage encountered to ground.
Arc welding and cutting cables should be
completely insulated, flexible, and capable of
handling the maximum current requirements of
the work as well as the duty cycle under which the
welder or cutter is working.
Avoid repairing or splicing cable within 10 feet
of the cable end to which the electrode holder is
connected. If necessary, use standard insulated
connectors or splices which have the same
insulating qualities as the cable being used.
Connections made with cable lugs must be securely
fastened together to give good electrical contact.
The exposed parts of the lugs must be completely
insulated. Do not use cables with cracked or damaged
insulation, or exposed conductors or end connectors.
A welding cable should have a safe current carrying
capacity equal to or exceeding the maximum
capacity of the welding or cutting machine.
The work lead, often incorrectly referred to as
the ground lead, should be connected as close as
possible to the location being welded to ensure
that the current returns directly to the source
through the work lead.Tools and Techniques 41-9
WELDING AND CUTTING
WARNING: Never use the following as part of the
• Cranes or hoists
• Chains or wire ropes
• Elevator structures
• Pipelines containing gases or flammable liquids
• Conduits containing electrical circuits.
A structure employed as a work lead must have
suitable electrical contact at all joints. Inspect
the structure periodically to ensure that it is still
safe. Never use any structure as a circuit when it
generates arc, sparks, or heat at any point.
The frames on all arc welding and cutting machines
must be grounded according to the CSA standard
or the regulatory authority. Inspect all ground
connections to ensure that they are mechanically
sound and electrically adequate for the required
• When electrode holders are to be left
unattended, remove electrode and place holder
so it will not make contact with other workers or
• Never change electrodes with bare hands or with
• Do not dip hot electrode holders in water to cool
• Keep cables dry and free of grease to prevent
premature breakdown of insulation.
• Cables that must be laid on the floor or
ground should be protected from damage and
• Keep welding cables away from power supply
cables and high tension wires.
• Never coil or loop welding cables around any part
of your body.
• Do not weld with cables that are coiled up or on
spools. Unwind and lay cables out when in use.
• Before moving an arc welding or cutting machine,
or when leaving machine unattended, turn the
power supply OFF.
• Report any faulty or defective equipment to your
• Read and follow the equipment manufacturer’s
• Prevent shock by using well-insulated electrode
holders and cables, dry clothing and gloves,
rubber-soled safety boots, and insulating material
(such as a board) if working on metal.
• All arc welding and cutting operations should
be shielded by non-combustible or flame-proof
screens to protect other workers from direct rays
of the arc.
• Shut off the power supply before connecting the
welding machine to the building’s electrical power.
• Keep chlorinated solvents shielded from the
exposed arc or at least 60 m (200 ft) away.
Surfaces prepared with chlorinated solvents must
be thoroughly dry before being welded. This is
especially important when using gas-shielded
metal-arc welding, since it produces high levels of
• Check for the flammability and toxicity of any
preservative coating before welding, cutting, or
heating. Highly flammable coatings should be
stripped from the area to be welded. In enclosed
spaces, toxic preservative coatings should be
stripped several inches back from the area of heat
application or the welder should be protected
by an airline respirator. In the open air, a suitable
cartridge respirator should be used. Generally, with
any preservative coating, check the manufacturer’s
SDS for specific details regarding toxicity and
personal protection required.
Oxyacetyelene Welding and Cutting
• Do not accept or use any compressed
gas cylinder which does not have proper
identification of its contents.
• Transport cylinders securely on a hand truck
whenever possible. Never drag them.
• Protect cylinders and any related piping and
fittings against damage.
• Do not use slings or magnets for hoisting
cylinders. Use a suitable cradle or platform.
• Never drop cylinders or let them strike each other
• Chalk EMPTY or MT on cylinders that are empty.
Close valves and replace protective caps.
• Secure transported cylinders to prevent
movement or upset.
• Always regard cylinders as full and handle
• For answers about handling procedures, consult
the manufacturer, supplier, or the SDS.
• Store cylinders upright in a safe, dry, well-ventilated
location maintained specifically for this purpose.
• Never store flammable and combustible materials
such as oil and gasoline in the same area.
• Do not store cylinders near elevators, walkways,
stairwells, exits, or in places where they may be
damaged or knocked over.
• Do not store oxygen cylinders within 6 m (20 ft)
of cylinders containing flammable gases unless
they are separated by a partition at least 1.5 m (5
ft) high and having a fire-resistance rating of at
least 30 minutes (Figure 41-14).
• Store empty and full cylinders separately.
• Prohibit smoking in the storage area.41-10 Construction Health and Safety Manual
WELDING AND CUTTING
Figure 41-14: Keep Oxygen and
Gas Cylinders Separated
• Use oxygen and acetylene cylinders in a proper
buggy equipped with a fire extinguisher (Figure
41-15). Secure cylinders upright.
• Keep the cylinder valve cap in place when the
cylinder is not in use.
• Do not force connections on cylinder threads that
do not fit.
• Open cylinder valves slowly. Only use the
handwheel, spindle key, or special wrench
provided by the supplier.
• Always use a pressure-reducing regulator with
compressed gases. For more information, see the
• Before connecting a regulator to a cylinder, crack
the cylinder valve slightly to remove any debris
or dust that may be lodged in the opening. Stand
to one side of the opening and make sure the
opening is not pointed toward anyone else, other
welding operations, or sparks or open flame.
• Open the fuel gas cylinder valve not more than
1 1/2 turns unless marked back-seated.
• Do not use acetylene pressure greater than 15 psig.
• Never allow sparks, molten metal, electric current,
or excessive heat to come in contact with
• Never bring cylinders into unventilated rooms or
• Never use oil or grease as a lubricant on the
valves or attachments of oxygen cylinders. Do not
handle with oily hands, gloves, or clothing. The
combination of oxygen and oil or grease can be
• Do not use oxygen in place of compressed air for
• Release pressure from the regulator before
removing it from the cylinder valve.
• When gas runs out, extinguish the flame and
connect the hose to the new cylinder. Purge the
line before re-igniting the torch.
• When work is finished, purge regulators, then
turn them off. Use a proper handle or wrench to
turn off cylinders.
Figure 41-15: Buggy Equipped with a Fire
Pressure regulators must be used on both oxygen
and fuel gas cylinders to maintain a uniform and
controlled supply of gas to the torch. The oxygen
regulator should be designed with a safety relief
valve so that, should the diaphragm rupture,
pressure from the cylinder will be released safely
and the regulator will not explode.
Each regulator (both oxygen and fuel gas) should
be equipped with a high-pressure contents gauge
and working pressure gauge. Always stand to one
side of regulator gauge faces when opening the
To prevent regulators from being installed on the
wrong cylinders, oxygen cylinders and regulators
have right-hand threads while most fuel gas
cylinders and regulators have left-hand threads.
Internal and external threads and different
diameters also help to prevent wrong connections.
Hoses and hose connections for oxygen and
acetylene should be different colours. Red is
generally used to identify the fuel gas and green
the oxygen. The acetylene union nut has a groove
cut around the centre to indicate left-hand thread.
• Protect hoses from traffic, flying sparks, slag, and
other damage. Avoid kinks and tangles.
• Repair leaks properly and immediately. Test for
leaks by immersing hose in water.
• Use backflow check valves and flame arrestors
according to the manufacturer’s instructions.
(See Figure 41-12.)
• Do not use a hose that has been subject to
flashback or that shows evidence of wear or
damage without proper and thorough testing.
Backfires occur when the flame burns back into the
torch tip, usually accompanied by a loud popping
sound. Backfires are usually caused by touching the
tip against the work or by using pressures that are
Flashback is much more serious. The flame burns
back inside the torch itself with a squealing or
hissing sound. If this happens, follow the torch
manufacturer’s instructions to extinguish the torch
in proper sequence.Tools and Techniques 41-11
WELDING AND CUTTING
• Keep cylinders away from sources of heat or
damage and secure them upright.
• Stand to one side and slightly crack cylinder
valves to blow out dust.
• Attach regulators to respective cylinders. Tighten
nuts with a proper wrench.
• Release pressure adjusting screws on regulators.
• Connect green hose to oxygen regulator and red
hose to fuel gas regulator.
• Connect hoses to the torch—green to oxygen
inlet and red to fuel gas inlet.
• Connect mixer and welding tip assembly to torch
• Open oxygen cylinder valve slowly and fully.
• Open fuel gas cylinder 3/4 to 11/2 turns.
• Open oxygen torch valve. Turn oxygen regulator
pressure adjusting screw to desired pressure.
Continue oxygen purge for about 10 seconds for
each 100 feet of hose. Close oxygen torch valve.
• Open fuel gas torch valve. Turn fuel gas regulator
pressure adjusting screw to desired pressure and
purge for about 10 seconds for each 100 feet of
hose. Close fuel gas torch valve.
• To light torch, follow the manufacturer’s
instructions. DO NOT USE MATCHES.
• Adjust to desired flame.
• Close torch valves according to the
• Close fuel gas cylinder valve.
• Close oxygen cylinder valve.
• Drain fuel gas cylinder line by opening torch
fuel gas valve briefly. Close valve. Drain oxygen
line in the same way.
• Re-open both torch valves.
• Release pressure adjusting screws on both
Regulators and torches can now be disconnected.
Many different makes, models, and designs of
torches are available. There is no single procedure
or sequence to follow in igniting, adjusting, and
extinguishing the torch flame. Always follow the
Silver Solder Brazing
Silver solder brazing is used for joining metals and
steel and disimilar metal combinations where it is
necessary to perform the joining of these metals at
low temperatures. Applications include medical and
laboratory systems, refrigeration, aerospace, and
electronic equipment. In brazing, the major hazards
are heat, chemicals, and fumes.
Fumes generated during brazing can be a serious
hazard. Brazing fluxes generate fluoride fumes
when heated. Cadmium in silver brazing alloys
vaporizes when overheated and produces cadmium
oxide, a highly toxic substance. Cadmium oxide
fumes inhaled into the respiratory tract can cause
pulmonary distress, shortness or breath, and in
cases of severe exposure may cause death.
The most serious cause of cadmium oxide fumes is
overheating the silver brazing filler metal. Care must
be taken to control the temperature of the silver
brazing operation. The torch flame should never be
applied directly to the silver brazing filler rod. The
heat of the base metal should be used to melt and
flow the brazing filler metal.
Cadmium-plated parts can be an even more
hazardous source of cadmium fumes, since in
brazing these parts the torch flame is applied
directly to the base metal. Cadmium plating should
be removed before heating or brazing. When in
doubt about a base metal, check with the supplier
of the part.
Safe Silver Solder Brazing
• Do not heat or braze on cadmium-plated parts.
• Read warning labels on filler metals and fluxes
and follow instructions carefully.
• Work in a well-ventilated area or use a suppliedair respirator.
• Apply heat directly to the base metal—not to the
brazing filler metal.
• Do not overheat either the base metal or the
brazing filler metal.
• Wash hands thoroughly after handling brazing
fluxes and filler metals.
Welding in enclosed or confined areas creates
additional hazards for the welder. The employer must
have a written rescue procedure for confined spaces.
In addition to the procedures outlined in the
chapter on confined spaces in this manual, take the
• Inspect all electrical cables and connections that
will be taken into the confined space.
• Perform leak tests on gas hoses and connections
to eliminate the risk of introducing gases into the
• Check for live electrical systems and exposed
• Use inspection ports, dipsticks, or a knowledgeable
person to evaluate hazards from any liquids, solids,
sludge, or scale left in the space.
• Ventilate space with clean air before entry and
maintain ventilation as long as necessary to
prevent the accumulation of hazardous gases,
fumes, and vapours.41-12 Construction Health and Safety Manual
WELDING AND CUTTING
• Different gases have different weights and may
accumulate at floor, ceiling, or in between. Air
monitoring should be done throughout the
• Isolate the space from any hydraulic, pneumatic,
electrical, and steam systems which may
introduce hazards into the confined area.
Use isolation methods such as blanks, blinds,
bleeding, chains, locks, and blocking of stored
energy. Tag isolated equipment.
• A competent person must test and evaluate the
atmosphere before workers enter a confined
space, and at all times during work there. A
hazardous atmosphere may already exist or gases
and vapours may accumulate from cutting or
welding. Oxygen content may become enriched
• Keep compressed gas cylinders and welding
power sources outside the confined space.
• Where practical, ignite and adjust flame for oxyfuel applications outside the space, then pass the
torch inside. Similarly, pass the torch outside the
space, then extinguish it.
• When leaving a confined space, remove the torch
and hoses and shut off gas supply.
• If adequate ventilation cannot be maintained, use
a suitable supplied-air respirator.
It is the responsibility of the employer to have a
written emergency rescue plan and communicate
the plan to all involved. Each person should know
what do to and how to do it quickly. (See Chapter
33: Confined Spaces in this manual.)
Personal Protective Equipment
In addition to the protective equipment required for
all construction workers (see chapters on personal
protective equipment in this manual), welders
should wear flame-proof gauntlet gloves, aprons,
leggings, shoulder and arm covers, skull caps, and
Clothing should be made of non-synthetic materials
such as wool. Woollen clothing is preferable to
cotton because it is less likely to ignite. Keep
sleeves rolled down and collars buttoned up. Wear
shirts with flaps over pockets and pants with no
cuffs. Remove rings, watches, and other jewelry.
Never carry matches or lighters in pockets. Clothing
should be free from oil and grease. Wear high-cut
CSA grade 1 footwear laced to the top to keep out
sparks and slag.
Protective screens or barriers should be erected
to protect people from arc flash, radiation, or
spatter. Barriers should be non-reflective and allow
air circulation at floor and ceiling levels. Where
barriers are not feasible or effective, workers near
the welding area should wear proper eye protection
and any other equipment required. Signs should be
posted to warn others of welding hazards.
Eye and Face Protection
Welding helmets provide radiation, thermal,
electrical, and impact protection for face, neck,
forehead, ears, and eyes. Two types are available—
the stationary plate helmet and the lift-front or
flip-up plate helmet. There are also auto-darkening
helmets that have a single pane of self-darkening
glass in the visor.
The lift-front type should have a fixed impactresistant safety lens or plate on the inside of the
frame next to the eyes to protect the welder
against flying particles when the front is lifted. All
combination lenses should have a clear impactresistant safety lens or plate next to the eyes.
There are also special models incorporating earmuff
sound arrestors and air purification systems.
Special prescription lens plates manufactured to
fixed powers are available for workers requiring
The typical lens assembly for arc welding is shown
in Figure 41-16. The filtered or shaded plate is the
radiation barrier. It is necessary to use a filter plate
of the proper lens shade to act as a barrier to the
harmful light rays and to reduce them to a safe
intensity. Guidelines for selection are in Table 41-1.
1st: Clear Glass
or Plastic Lens
The arc welding lens
of 3 parts. The
outside lens is clear
plastic or tempered
glass. It protects
the shade lens from
damage. The centre
lens is a shade lens
that filters out the
harmful light. The
inner lens is clear
and must be plastic.
Figure 41-16: Typical Lens Assembly for Arc Welding
In addition to common green filters, many special
filters are available. Some improve visibility by
reducing yellow or red flare. Others make the
colour judgment of temperature easier. Some have
a special gold coating on the filter lens to provide
additional protection by reflecting radiation.
Welding hand shields are designed to provide
radiation and impact protection for the eyes and
face. They are similar to welding helmets except
that there are no lift-front models.
Spectacles with full side shields designed to protect
against UV radiation and flying objects and suitable
filter lenses should always be worn in conjunction
with full welding helmets or welding hand shields.
Where only moderate reduction of visible light is
required (for instance, gas welding) use eyecup
or cover goggles with filter lenses for radiation
protection. Goggles should have vents to minimize
fogging and baffles to prevent leakage of radiation
into the eye cup.Tools and Techniques 41-13
WELDING AND CUTTING
Welders should not wear contact lenses because
airborne dust and dirt may cause excessive
irritation of the eyes under the lenses.
Table 41-1: Lens Shade Selection Guide for Welding
Electrode Arc Minimum Suggested*
Size Current Protective Shade No.
Process mm (in) (Amperes) Shade (Comfort)
Shielded Metal less than 2.4 (3/32) less than 60 7 –
Arc Welding 2.4-4 (3/32-5/32) 60–160 8 10
(SMAW) 4-6.4 (5/32-1/4) 160–250 10 12
more than 6.4 (1/4) 250–550 11 14
Gas Metal Arc Welding less than 60 7 –
and Flux Cored 60–160 10 11
(GMAW) 160–250 10 12
250–550 10 14
Gas Tungsten Arc Welding less than 50 8 10
(GTAW) 50–150 8 12
150–500 10 14
Air Carbon (light) less than 500 10 12
Arc Cutting (heavy) 500–1,000 11 14
Plasma Arc Welding less than 20 6 6 to 8
(PAW) 20–100 8 10
100–400 10 12
400–800 11 14
Plasma Arc Cutting (PAC)
less than 20 4 4
20–40 5 5
40–60 6 6
60–80 8 8
80–300 8 9
300–400 9 12
400–800 10 14
Torch Brazing (TB) – – 3 or 4
Torch Soldering (TS) – – 2
Carbon Arc Welding (CAW) – – – 14
Light under 3 under 1/8 4 or 5
Medium 3 to 13 1/8 to 1/2 5 or 6
Heavy over 13 over 1/2 6 to 8
Oxygen Cutting (OC)
Light under 25 under 1 3 or 4
Medium 25 to 150 1 to 6 4 or 5
Heavy over 150 over 6 5 or 6
Source: ANSI Z49.1: 2012—Safety in Welding, Cutting, and
Reproduced with the permission of the American
NOTE: Shade numbers are given as a guide only and may
be varied to suit individual needs.
*As a rule of thumb, start with a shade that is too dark
to see the weld zone. Then go to a lighter shade which
gives sufficient view of the weld zone without going
below the minimum. In oxy-fuel gas welding, cutting, or
brazing where the torch and/or the flux produces a high
yellow light, it is desirable to use a filter lens that absorbs
the yellow or sodium line of the visible light spectrum.
The employer is responsible for assessing the
risk of hearing loss from exposure to noise and
developing a plan to control or eliminate that risk. If
hearing protection devices (HPDs) are considered
appropriate, earplugs may be a better choice for
welders than earmuffs, which can be cumbersome
and interfere with the welding helmet. Training on the
selection, use, and care of HPDs must be provided.
See Chapter 14: Hearing Protection in this manual.
Welders should have their hearing checked every
year or so. A simple test can be arranged through
your doctor. Once hearing is damaged, the loss is
likely permanent. Checkups can detect any early
losses and help you to save your remaining hearing.
Radiographic and X-Ray Testing
Some construction trades will encounter situations
in which welds, metals, or special coatings require
onsite non-destructive testing.
1) radiography using a radioactive source for
2) x-rays for testing thicker sections.
Radiography is federally regulated across Canada
by the Atomic Energy Control Board. Users
must be licensed and operators must be trained
according to a Canadian Government Standards
Board (CGSB) program.
X-ray testing is provincially regulated—in Ontario
by Regulation 861/90. While many requirements
apply to licensed users in both situations, this
section will only cover the basic health and safety
guidelines for field use.
Licensed users of radiographic testing systems
are responsible for general safety in the field,
transportation, emergency procedures, and
Radiographic testing must be carried out in the
presence of persons certified to CGSB Standard
48GP4a. In general, these people are employees of
a recognized testing agency.
Radiographic materials and equipment must be
kept locked up in shielded storage containers
accessible only to certified personnel. The
containers must be conspicuously marked and kept
in an area not normally occupied by the workforce.
There may be other special requirements which
apply, depending on the strength of the radioactive
source and the location.
Radiographic cameras in the field must be
used in conjunction with pocket dosimeters,
survey meters, directional shields, barrier ropes,
radiographic warning signs, and an emergency
source container.41-14 Construction Health and Safety Manual
WELDING AND CUTTING
General Safety Precautions
• Radiographic testing should be conducted,
whenever possible, on an off-shift with as
few workers as possible in the work area. The
radiographic source should be no stronger than
is required for the job. Determining the strength
of the source is not generally the responsibility of
construction site personnel.
• Equipment should be checked before use. The
regulation includes a list of items to be checked,
but doing so is not usually the responsibility of
• After taking tests where the camera will be
moved, the area should be checked using a
• Licensed users are required to keep records
regarding the use of sources, including dates,
times, locations, and other details. These records
must be made available to inspectors from the
Atomic Energy Control Board. Users are also
responsible for advising the local fire department
when radioactive material will be in a municipality
for longer than 24 hours.
Specific requirements for radiographic camera
users are the responsibility of the certified persons
operating the equipment.
• The survey meter must be checked to ensure that
it is working and calibrated properly.
• Barrier ropes should be set up around the area
where testing will be carried out unless this area is
isolated and access can be controlled. Barriers must
be set up according to the strength of the source.
• Warning signs must be posted along the barriers.
• A patrol must be provided to ensure that no
unauthorized persons enter the testing area.
• Before the camera shutter is opened and testing
is conducted, the area must be properly shielded.
• Personnel working within the testing area should
carry personal dosimeters. Dosimeters may also
be advisable for workers in the immediate vicinity
outside the barriers.
The following health and safety precautions are
required for the x-ray testing of welds and metals:
• A suitable means to prevent unauthorized
persons from activating the equipment
• A device to indicate when the x-ray tube is
• Housing that adequately shields the equipment
Employers using x-ray equipment must advise the
MOL that they have such equipment. They must
also designate certain persons to be in charge
of the x-ray equipment who are trained and
competent to do so. They must give the MOL the
names of these designated persons.
Measures and procedures at the x-ray testing
site are similar to those required for radiographic
testing. The following are the employer’s
• Test during off-shifts.
• Cordon off the test area if it cannot be isolated or
if entry cannot be controlled.
• Post warning signs along the barrier or at the
entrance to the room where testing is taking
• Have a patrol to prevent unauthorized entry.
• Install shielding as required before any equipment
• Ensure that employees in the controlled area
wear personal dosimeters.
• Keep dosimeter records.
• Keep at least one radiation survey meter of a
suitable type with each portable x-ray machine
and calibrate it at least once each year.
Welders, fitters, and welding supervisors should
be trained in both the technical and safety aspects
of their work. Health and safety training should
include but not be limited to the following.
• Hazard identification
• Safe welding, brazing, and cutting practices
• Fire and safety precautions
• Control methods for welding hazards
• Use, maintenance, and limitations of personal
The effectiveness of health and safety training
should be periodically evaluated through the
• A workplace inspection to ensure that safe
working procedures, equipment, and conditions
• Air monitoring of common contaminants to
determine the effectiveness of controls and
compliance with acceptable limits
• An assessment of control performance (for
instance, testing of the ventilation system)
• Review of lost-time-injuries
• Discussion of the program with the health and
safety committee or representative(s).
Any corrective actions necessary should be taken
كلمة سر فك الضغط : books-world.net
The Unzip Password : books-world.net