Category: Hot Work

welding fumes:

Welding fumes are a complex mixture of metallic oxides, silicates and fluorides. Fumes are formed when a metal is heated above its boiling point and its vapours condense into very fine, particles (solid particulates).

Composition of welding fumes vary:

Yes, welding fumes contain oxides of the metals in the material being welded.

• Fluxes containing silica or fluoride produce amorphous silica, metallic silicates and fluoride fumes.

• Fumes from mild steel welding contain mostly iron with small amounts of additive metals. .(chromium, nickel, manganese, molybdenum, vanadium, titanium, cobalt, copper etc.).

• Stainless steels have larger amounts of chromium or nickel in the fume and lesser amounts of iron.

• Nickel alloys have much more nickel in the fume and very little iron.

How do coatings change the composition of welding fumes:

Vapours or fumes can come from coatings and residues on metal being welded. Some ingredients in coatings can have toxic effects. These ingredients include:

• metal working fluids, oils and rust inhibitors.

• zinc on galvanized steel (vaporizes to produce zinc oxide fume).

• cadmium plating.

• vapours from paints and solvents.

• lead oxide primer paints.

• some plastic coatings.

Metal Coatings – A Source of Hazardous Fumes

How do I remove the coatings?

• Remove coatings from the weld area to minimize the fume. The removal of coating will also improve weld quality.

• Use stripping products to remove coatings. Make sure to remove any residues before welding.

• Use wet slurry vacuum removal techniques for removing very toxic coatings.

• Do not grind coatings. Grinding dust may be toxic.

What are welding gases?

Welding gases are gases used or produced during welding and cutting processes like shielding gases or gases produced by the decomposition of fluxes or from the interaction of ultraviolet light or high temperatures with gases or vapours in the air.

Examples of welding gases:

Gases used in welding and cutting processes include:

• shielding gases such as carbon dioxide, argon, helium, etc.

• fuel gases such as acetylene, propane, butane, etc.

• oxygen, used with fuel gases and also in small amounts in some shielding gas mixtures

Gases produced from welding and cutting processes include:

• carbon dioxide from the decomposition of fluxes.

• carbon monoxide from the breakdown of carbon dioxide shielding gas in arc welding.

• ozone from the interaction of electric arc with atmospheric oxygen.

• nitrogen oxides from the heating of atmospheric oxygen and nitrogen.

• hydrogen chloride and phosgene produced by the reaction between ultraviolet light and the vapours from chlorinated hydrocarbon degreasing solvents (e.g., trichloroethylene, TCE).

Gases are also produced from the thermal breakdown of coatings:

• Polyurethane coatings can produce hydrogen cyanide, formaldehyde, carbon dioxide, carbon monoxide, oxides of nitrogen, and isocyanate vapours.

• Epoxy coatings can produce carbon dioxide and carbon monoxide.

• Vinyl paints can produce hydrogen chloride.

• Phosphate rust-inhibiting paints can release phosphine during welding processes.

• Minimizing exposure to degreasing solvent vapours.

Hot work:

Working with ignition sources near flammable materials is referred to as “hot work.” Welding and cutting are examples of hot work. Fires are often the result of the “quick five minute” job in areas not intended for welding or cutting. Getting a hot work permit before performing hot work is just one of steps involved in a hot work management program that helps to reduce the risk of starting a fire by welding or cutting in areas where there are flammable or combustible materials.

The National Fire Protection Association (NFPA) Standard 51B “Fire Prevention in the Use of Cutting and Welding Processes” serves as the basis for the fire codes and many fire prevention practices adopted by industry.

Some general good practices:

Make sure you are following your hot work procedure. Also consider the follow items:

• Make sure that all equipment is in good operating order before work starts.

• Inspect the work area thoroughly before starting. Look for combustible materials in structures (partitions, walls, ceilings).

• Sweep clean any combustible materials on floors around the work zone. Combustible floors must be kept wet with water or covered with fire resistant blankets or damp sand.

• Use water ONLY if electrical circuits have been de-energized to prevent electrical shock.

• Remove any spilled grease, oil, or other combustible liquid.

• Move all flammable and combustible materials away from the work area.

• If combustibles cannot be moved, cover them with fire resistant blankets or shields. Protect gas lines and equipment from falling sparks, hot materials and objects.

• Block off cracks between floorboards, along baseboards and walls, and under door openings, with a fire resistant material. Close doors and windows.

• Cover wall or ceiling surfaces with a fire resistant and heat insulating material to prevent ignition and accumulation of heat.

• Secure, isolate, and vent pressurized vessels, piping and equipment as needed before beginning hot work.

• Inspect the area following work to ensure that wall surfaces, studs, wires or dirt have not heated up.

• Vacuum away combustible debris from inside ventilation or other service duct openings to prevent ignition. Seal any cracks in ducts. Prevent sparks from entering into the duct work. Cover duct openings with a fire resistant barrier and inspect the ducts after work has concluded.

• Post a trained fire watcher within the work area during welding, including during breaks, and for at least 30-60 minutes after work has stopped. Depending on the work done, the area may need to be monitored for longer (up to 3 hours) after the end of the hot work.

• Eliminate explosive atmospheres (e.g., vapours or combustible dust) or do not allow hot work. Shut down any process that produces combustible atmospheres, and continuously monitor the area for accumulation of combustible gases before, during, and after hot work.

• If possible, schedule hot work during shutdown periods.

• Comply with the required legislation and standards applicable to your workplace.

Type of PPE is available when welding:

The chart below summarizes the types of personal protective equipment that can be used when welding.

Eye and face protection is appropriate for my welding task:

The various types of eye protection are broken down into classes in the Canadian Standards Association (CSA) standard Z94.3.1 “Selection, use, and care of protective eyewear”.  Each class has a specific use that it has been designed for.  Common protectors for welding operations are listed below:

• Class 2C – direct non-ventilated goggles with radiation protection

• Class 3 – welding helmets

• Class 4 – hand shields

• Class 5C – non-rigid helmets with radiation protection

• Class 6B – faceshields with radiation protection

• Class 7B – respirator facepiece with radiation protection

The following operations require full face protection from either a welding helmet or a hand shield:

• arc welding,

• plasma arc cutting, gouging or welding, and

• air carbon arc cutting.

For gas cutting, welding, or brazing, the intensity of the light is much less than from arc welding, cutting or gouging processes.  Lighter shade filter lenses can be used with goggles in place of a helmet.

Various components of welding hand shields and helmets:

Hand shields or helmets provide eye protection by using an assembly of components:

• Helmet shell – must be opaque to light and resistant to impact, heat and electricity.

• Outer cover plate made of polycarbonate plastic which protects from UV radiation, impact and scratches.

• Filter lens made of glass containing a filler which reduces the amount of light passing through to the eyes. Filters are available in different shade numbers ranging from 2 to 14. The higher the number, the darker the filter and the less light passes through the lens.

• Clear retainer lens made of plastic prevents any broken pieces of the filter lens from reaching the eye.

• Gasket made of heat insulating material between the cover lens and the filter lens protects the lens from sudden heat changes which could cause it to break. In some models the heat insulation is provided by the frame mount instead of a separate gasket.

Tips to know when using protective clothing:

DO

• Wear clothing made from heavyweight, tightly woven, 100% wool or cotton to protect from UV radiation, hot metal, sparks and open flames. Flame retardant treatments become less effective with repeated laundering.

• Keep clothing clean and free of oils, greases and combustible contaminants.

• Wear long-sleeved shirts with buttoned cuffs and a collar to protect the neck. Dark colours prevent light reflection.

• Tape shirt pockets closed to avoid collecting sparks or hot metal or keep them covered with flaps.

• Pant legs must not have cuffs and must cover the tops of the boots. Cuffs can collect sparks.

• Repair all frayed edges, tears or holes in clothing.

• Wear high top boots fully laced to prevent sparks from entering into the boots.

• Use fire-resistant boot protectors or spats strapped around the pant legs and boot tops, to prevent sparks from bouncing in the top of the boots.

• Remove all ignition sources such as matches and butane lighters from pockets. Hot welding sparks may light the matches or ignite leaking lighter fuel.

• Wear gauntlet-type cuff leather gloves or protective sleeves of similar material, to protect wrists and forearms. Leather is a good electrical insulator if kept dry.

• Direct any spark spray away from your clothing.

• Wear leather aprons to protect your chest and lap from sparks when standing or sitting.

• Wear layers of clothing. To prevent sweating, avoid overdressing in cold weather. Sweaty clothes cause rapid heat loss. Leather welding jackets are not very breathable and can make you sweat if you are overdressed.

• Wear a fire-resistant skull cap or balaclava hood under your helmet to protect your head from burns and UV radiation.

• Wear a welder’s face shield to protect your face from UV radiation and flying particles.

DO NOT

• Do not wear rings or other jewellery.

• Do not wear clothing made from synthetic or synthetic blends. The synthetic fabric can burn vigorously, melt and produce bad skin burns.

Identifying the hazards:

The first step in managing risks associated with welding processes is to identify all the hazards that have the potential to cause harm.

Welding and allied processes can have similar hazards and you can follow the same process to identify hazards. For example both welding and allied processes produces ultra violet and infra-red radiation which can cause burns, cancer and blindness.

Potential hazards may be identified in a number of different ways including:

• conducting a walk through assessment of the workplace observing the work and talking to workers about how work is carried out.inspecting the materials and equipment that will be used during the welding process.

• reading product labels, SDSs and manufacturer’s instruction manuals.

• talking to manufacturers, suppliers, industry associations and health and safety specialists.

• reviewing incident reports.

Assessing the risks:

A risk assessment involves considering what could happen if someone is exposed to a hazard combined with the likelihood of it happening.

Under the Regulations a risk assessment is not mandatory for welding however, it is required for specific situations, for example when working in a confined space.

In some circumstances, a risk assessment will assist to:

• identify which workers are at risk of exposure.

• determine what sources and processes are causing that risk.

• identify if and what kind of control measures should be implemented.

• check the effectiveness of existing control measures.

Risks will depend on various factors, including the:

• properties of the materials being welded.

• surface coating of the items being welded (for example whether they contain lead
  or other toxic materials).

• condition of the welding equipment.

• conditions under which welding is carried out (for example, confined spaces).

• skills, competence and experience of the welder.

Different welding processes also influence the risk. For example, the risk of electric shock is lower using gas metal arc welding than manual metal arc welding because the open circuit voltages are lower, only direct current is used and the power is switched at the hand piece.

The following questions may help to assess the risk:

• In the event of exposure to the hazard, will the outcome be severe, moderate or mild?

• How often, and for how long, will exposure to the hazard occur?

Controlling the risks:

The hierarchy of control measures

Some control measures are more effective than others. Control measures can be ranked from the highest level of protection and reliability to the lowest. This ranking is known as the hierarchy of control.

You must always aim to eliminate a hazard and associated risk first. For example, fabrications may be designed to include many pre-cast components or extruded shapes to eliminate the need to weld.

If this is not reasonably practicable, the risk must be minimised by using one or more of the following approaches:

• Substitution – replace a hazardous process or material with one that is less hazardous, for example using submerged arc welding instead of flux-cored wire welding will reduce the risk of exposure to radiation and fumes. In welding, such types of substitution are not always practical or technically suitable.

• Isolation – removing the welder and nearby workers from the hazard or isolating or screening the hazard from the welder, for example ancillary processes like plasma cutting, gouging, grinding, fettling and guillotining can be carried out in specified areas away from general fabrication, to reduce risk of exposure to loud noise at the welding station.

• Engineering controls – use engineering control measures to minimize the risk, for example, ventilation systems to remove welding fumes.

If risk then remains, it must be minimized by implementing administrative controls, so far as is reasonably practicable. For example, if a welding process takes place in a very hot environment, allowing the welder to weld for a limited time followed by a suitable rest and cooling-off period will reduce the risk of heat exhaustion.

Any remaining risk must be minimized with suitable personal protective equipment (PPE). For example, if the welder has to stand on metallic surfaces that form part of the electric circuit it may become live. The use of rubber-soled boots will reduce the risk of electric shock.

Administrative control measures and PPE rely on human behavior and supervision. If used on their own, they tend to be least effective in minimizing risks.

A combination of these control measures may be required in order to adequately manage the risks with welding. You should check that your chosen control measure does not introduce new hazards.

Reviewing control measures:

The control measures that are put in place to protect health and safety should be regularly reviewed to make sure they are effective. This may involve, for example, atmospheric monitoring  to measure the amount of welding fume in the welder’s breathing zone following introduction of fume extraction equipment. If the control measure is not working effectively it must be revised.

Common review methods include workplace inspection, consultation, testing and analysing records and data.

If problems are found, go back through the risk management steps, review your information and make further decisions about controlling the risk.

Electrical risks

Using electrical welding equipment involves a risk of electric shock or electrocution. Exposure to electromagnetic fields is also a potential hazard for workers with some medical conditions.

Electric shock:

Electric shock may result in serious burns or death by electrocution. Electric shock or electrocution can occur through direct contact with the electrode, live parts, the work piece, or through contact with a device such as an unearthed cable or tool. The risk of electric shock can be exacerbated by moisture and high humidity.

Control measures

• Use fully insulated electrode holders. The holder should never be dipped into water to cool, or be placed on conductive surfaces.

• Prevent contacting electrodes or welding wire with bare hands when in the holder or welding gun (wear dry welding gloves), and make sure that holders or welding guns are never held under the armpits.

• Prevent holders or electrodes coming into contact with any other person.

• Check the working area does not have any potentially live structures, components or wet areas.

• Install a RCD.

• Inspect all equipment to check that it is in good condition prior to use,including power switches, terminals, connections, cables and insulation.

The working environment should be designed to minimise the risk of electric shock. For example, areas where welding is undertaken, can be insulated and air-ventilated to prevent workers from perspiring as perspiration is a conductor of electricity.

Table 1 below lists several ways to minimise the risk of electric shock when carrying out welding.

Electric arc welding produces strong electric and magnetic fields close to the power source  and around the current-carrying cables. Electromagnetic fields can disrupt the operation of pacemakers, permanent defibrillators or other medical devices which could cause the heart to stop or slow down. A worker will not be aware of a magnetic field hazard unless a heart pacemaker or other device is behaving irregularly.

Electromagnetic fields can also occur wherever power is being generated and near transmission lines. Before work near these facilities begins, you should check with the electricity supply company to make sure work will not affect the supply of power or if there are any special precautions welders need to take when working in those areas.

Control measures:

• Use barriers to isolate people who are not directly involved in the welding process.

• Use signs indicating there are strong electromagnetic fields should be used to alert people to risks.

• Workers should not stand close to the power source or drape the welding cable around their body.

• Workers with pacemakers or other susceptible devices should substitute work that involves exposure to electromagnetic fields for another type of welding process, such as performing oxy-fuel welding instead of electric arc welding. Seek medical advice before exposing a worker wearing such a device to welding related electromagnetic fields.

Ventilation:

Ventilation can remove heat from the environment and reduce exposure to fumes &other atmospheric contaminants in the work area.

There are three main types of ventilation:

• local exhaust ventilation

• forced dilution ventilation.

• natural dilution ventilation.

The choice of ventilation system should take into account:

• the amount and type of fumes and contaminants produced.

• the proximity and location of the welding process relative to the ventilation system.

• the level of ventilation, natural or mechanical, both for the whole workplace and the  welding area – this will also depend on screens and partitions which may restrict cross-flow at the work area.

• the proximity of the welder’s breathing zone to the fume source.

Local exhaust ventilation:

A local exhaust system may comprise the elements listed:

• a hood which captures the contaminant close to its point of generation.

• a duct system to move contaminant away from the work area.

• an air cleaning system to prevent pollution of the general atmosphere.

• an exhaust fan to provide air flow.

• a stack or other means of discharging the decontaminated air into the atmosphere.

Local exhaust ventilation systems should be designed to provide a minimum capture velocity at the fume source of 0.5m/second away from the welder. Inlets and outlets should be kept clear at all times. Air from a local exhaust ventilation system should not be re-circulated into the workroom. This air should be discharged into the outside air away from other work areas and away from air conditioning inlets or compressors supplying breathing air.

Examples of local exhaust ventilation suitable for welding operations include:

• fixed installations, such as side-draught or down-draught tables and benches, and partially or completely enclosed booths.

• portable installations, such as movable hoods that are attached to flexible ducts (for example, see Figure 1).

• low volume high velocity fume extractors attached directly to the welding gun (for example, see Figure 2).

Forced dilution ventilation:

An elevated concentration of atmospheric contaminants can be diluted with a sufficient volume of clean air. Successful dilution ventilation depends not only on the correct exhaust volume but also on control of the airflow through the workplace. Although forced dilution ventilation systems are not as effective in controlling atmospheric contaminants as local exhaust ventilation systems, they may be useful to control minor emissions of low toxicity contaminants.

Figure 1: Local Exhaust ventilation in confined space welding

Figure 2: Fume extraction attached to the welding gun

Natural ventilation:

Natural ventilation should only be used for general comfort not as an engineered control measure for atmospheric contaminants and fumes.Natural ventilation can assist with the transfer ofcontaminants from the work area however it is not a reliable way of diluting or dispersing contaminants. For example, if a worker is working in a fixed position and the natural wind velocity is mild or wind is in a direction towards the worker, the worker may remain exposed to contaminants that have not been removed from the worker’s breathing zone.Personal protective equipment (PPE)

In most cases PPE must be worn by workers when welding to supplement higher levels of controls such as ventilation systems or administrative controls (see Figure 3).

Figure 3: Welder wearing welding helmet, dry leather welding gloves and leather apron

When PPE is worn by workers, it should not introduce other hazards to the worker, such as musculoskeletal injuries, thermal discomfort, or reduced visual and hearing capacity

The types of PPE recommended for use in welding are summarised in the following table:

SOURCE AND HEALTH EFFECT OF WELDING FUMES:

SOURCE AND HEALTH EFFECT OF WELDING GASES:

SOURCE AND HEALTH EFFECT OF ORGANIC VAPOURS AS A RESULT OF WELDING:

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