This Module in the Welding Institute of Canada’s series on “Fundamentals of Welding Technology” is aimed at creating a general awareness of health and safety aspects of welding and related processes. It is intended to provide a background for welders, welding supervisors, technicians, and others that may use or become involved with welding processes. But because safety procedures depend on specific conditions, equipment, or local regulations, the module can only treat the subject in general terms. Different or additional safety practices may be appropriate for specific situations and expert advice may need to be sought.
After successfully completing this module you should be able to:
Describe the WHMIS system and understand die meaning of warning labels
list important hazards in using welding and related processes
Describe means of avoiding electrical shocks
Describe how the welder can be protected from arc rays, heat and bums
Recognize when special ventilation is required to control fumes
List hazards associated with the use of gases and describe general safety practices
Explain how fires and explosions can be avoided
Describe safety practices for welding and cutting in confined spaces
List some of the hazards associated with less common welding processes.
CREATING A SAFE WORK ENVIRONMENT
Nearly all industrial operations indeed, virtually all human activities entail potential risks to health and safety. Welding and related activities expose the worker and those nearby to certain hazards ranging from fire and electric shock to eye damage and long term health effects. Minimizing these hazards is the joint responsibility of the employer and the worker the employer must inform the worker about the hazards and provide a safe working environment; the worker must use protective equipment and follow safety procedures. Some general rules for promoting a safe working environment are:
use a safe method of working. If in doubt, ask
follow health and safety procedures, respect warning signs, and always read safety labels
use personal protective clothing and equipment where required
ensure equipment is maintained in a safe condition and report defective or unsafe equipment
do not use any material or process until the hazards are known
exercise good housekeeping practices
do not ester any restricted area unless authorized
do not defeat the purpose of any safety features of equipment
Many laws are applicable to health and safety aspects of welding. Legislation varies from place to place and will not be discussed in detail, but several important points will be mentioned. Recent laws embody the idea of the “right to know” of persons in the workplace. The idea is that anyone in the workplace has the right to know about the hazards of materials they may be exposed to or work they may have to undertake. Some laws specifically give the worker the right to refuse to undertake work if he or she has reason to believe that it is unsafe.
In the USA the Occupational Safety and Health Administration (OSHA) is the federal body that regulates health and safety in the workplace and which the majority of states follow in their legislation. OSHA may, for example, require labels on products that identify carcinogenic potential. OSHA may also set limits for the exposure to specific materials that present a hazard to health.
In Canada, health and safety in the workplace is subj ect to provincial legislation except for federally regulated industries such as the national railways. In Ontario, for example, the Occupational Health and Safety Act covers such things as safety committees, rights of workers to be informed about potential hazards, “designated” substances that are regulated in specific ways, and exposure limits.
The health and safety acts of all the provinces have recently been amended to implement the federal “Workplace Hazardous Materials Information System” (WHMIS). This has resulted in a Canada-wide system in effect since 31 October 1988.
Under the idea of “right to know” the objective of WHMIS is to ensure that information on hazardous materials gets to all those in the workplace that could be exposed to the hazard. At the present time it only covers toxins and chemicals but not physical agents such as noise or ultraviolet light Physical agents, however, may be regulated under the provincial health and safety laws, and it is likely that WHMIS will be extended to cover physical agents in the future.
Under WHMIS, information is conveyed by three method
Material Safety Data Sheets (MSDS)
Hazardous materials are those meeting specific criteria (listed on the following page) under the Hazardous Products Act and are called Controlled Products. There is no list of controlled products; anything meeting the criteria is included. Controlled products are assigned to one or more of six classes which are listed on the following page with their corresponding symbols shown in Fig. 1
Class A: Compressed Gas Materials such as carbon dioxide, and argon that are gases at room temperature (20°Q and are kept under pressure.
Class B: Flammable and Combustible Materials that will ignite and continue to bum when exposed to a flame. A flammable liquid is one with a flash point less than 37.8°C (100°F) and a combustible liquid is one with a flash point greater than 37.8°C. The flash point is the minimum temperature at which the liquid gives off enough vapour to ignite undo- test conditions.
Examples: Flammable: gasoline, ethyl alcohol Combustible: kerosene, creosote.
Class C: Oxidizing
Materials, such as oxygen itself or potassium chlorate, that will cause another to bum.
Class D: Poisonous and Bio-hazardous Infectious
Materials causing immediate serious toxic effects when taken into the body.
Those that cause other toxic effects such as long term effects on health. Carcinogens (cancer causing) axe in this class.
Materials (organisms) that may cause infectious diseases. For example, certain bacteria and viruses.
Class E: Corrosive
Materials that will destroy human tissue and other materials. For example, sulphuric add.
Class F: Dangerously Reactive
Materials that by chemical reaction with another substance or self reaction when heated or pressurized may create a hazard. A material that produces a poisonous gas on contact with water would be in this class. But explosives are covered under a separate law—not WHMIS
Many materials used in, or associated with, welding operations may be classified as hazardous and come under WHMIS. Examples are
Oxygen and other gases for cutting and welding
Materials to be welded.
Any controlled product coming into or produced in a workplace must have an identifying label (supplier label) affixed to the container or package, hi addition, labels are also required in the workplace (workplace labels) to ensure that the information is transmitted to the end user of the material. Workplace labels must also be placed on controlled products decanted from their original containers into another at the workplace.
Labels must not be altered or destroyed since that would defeat the purpose of WHMIS and might expose someone to a hazard that they were unaware of. WHMIS labels have a characteristic appearance recognizable by the border. The supplier labels (Fig. 2) contain the following information.
Product identifier (common name, brand name, code, etc.)
Supplier identifier (name of supplier)
MSDS statement (says that a Material Safety Data Sheet is available)
Hazard symbol (one or more of the standard symbols)
Risk phrases (they describe the effects of exposure, e.g., “spontaneously flammable”)
Precautionary measures (how to avoid the risk, e.g., “store in designated area, no smoking”)
First aid measures (actions to be taken in the event of exposure, e.g., “wash affected area with running water”
Workplace labels contain less information than supplier labels and only give:
Safe handling instructions
If a supplier feels that providing this information gives away trade secrets, he may apply to an impartial review commission set up under the Hazardous Materials Information Review Act (HMIRA) for an exemption. The WHMIS supplier label adopted by the Welding Products Manufacturers Association of Canada (WPMAC) is shown in Fig. 3.
The WHMIS label alerts the user to a hazard but obviously does not have enough room to provide detailed information. The supplier must, therefore, provide a Material Safety Data Sheet (MSDS) for each controlled product supplied, and this must be accessible to anyone who requires it. The MSDS contains nine categories of information
fire or explosion hazard
first aid measures.
While some of the information in an MSDS is likely to be highly technical and would be used by engineers or safety officers, other parts provide valuable safety information. Hence MSDS's must be made available to all workers who use or may be exposed to controlled products. An example of some of die information in an MSDS used in a welding context is illustrated in Fig. 4
Under the WHMIS system instruction must be provided for employees who are exposed to controlled products. The training must be tailored to the specific job, materials, and hazards that the worker encounters.
General Hazards in the Shop
Welding personnel working in a shop will be exposed to potential hazards in addition to those directly associated wife welding. For example, overhead cranes may be moving large pieces of steel around, various pieces of machinery may be operating, or radiography may be being performed in a section of the shop. Likewise, other people not directly involved in welding, including occasional visitors to the shop, may be exposed to the hazards of welding, such as arc radiation, spatter, and fume.
Many of the hazards in the shop environment are fairly apparent by their nature. We may call these ‘inherent’ hazards and examples include:
machinery operation (mechanical hazards)
noise, arc radiation
welding sparks, spatter, open flames
vehicles, cranes, and moving material.
Less obvious hazards—which we may call ‘latent’ hazards—may be just as important, but perhaps the worker is less aware of them. Latent hazards might include:
working with unfamiliar equipment
work around or in tanks or confined spaces
fumes and gases
improper electrical connections
unmarked hot metal.
Guidance on Welding Health and Safely
The following sections in this module cover health and safety aspects of welding and related operations. There are many other sources of information and some of these are listed at the end of the module. Health and safety in welding is also covered by national standards. In Canada: CAN/CSA W117.2 “Safety in Welding, Cutting, and Allied Processes” and in die USA: ANS3/AWS Z49.1-94 “Safety in Welding and Cutting.”
GENERAL HAZARDS IN WELDING AND THEIR CONTROL
Identifying welding hazards
The first step in defining safety practices for welding is to define the potential hazards. These, of course, may be different for each situation, but CSA W117.2 provides some guidance on die general hazards that are associated with the common welding processes. Table 1 summarizes this information showing where a major hazard exists for four groups of welding processes.
Facts about electricity
Before discussing electrical hazards it is worth reviewing some basic facts about electricity. The amount of electricity flowing through a circuit is called the current (given die symbol, I) and is measured in amperes (A). To measure the current an ammeter is placed in the circuit so all the current flows through the ammeter. Currents in welding circuits can be very high, usually several hundred amperes.
The electromotive force, or force that is trying to push the current through the circuit, is measured in volts (V). The voltage is measured by placing a voltmeter across two points in a circuit. Fig. 5 illustrates how voltage and current are measured. The resistance (R) is a property.
of the material in the circuit and determines how much current is allowed to flow when a given voltage is placed across the circuit It is measured in ohms (Q). Materials with very low resistance, such as copper, are called conductors and allow large amounts of current to flow for a given voltage. The voltage, current, and resistance are linked by Ohm’s Law: I=V/R
The line or mains voltages available in shops axe high: typically 480 V (USA), 575 V (Canada) for three phase, and 240 V and 120 V for single phase. These are the primary voltages that are the inputs to electrical equipment Li most equipment these voltages are “stepped down” by a transformer to provide lower secondary voltages as shown in Fig. 6. The voltage across the output terminals of most welding machines is about 80 V when no current is drawn (the open circuit voltage, OCV) butit drops to 20 to 30 V when the arc is established and current is flowing. Open circuit voltages are limited by the National Electrical Manufacturers Association (NEMA) Standard EW-1 and are given in Table 2.
It is important to distinguish clearly between the primary and secondary rides of electrical equipment because of the difference in voltages.
The human body can conduct electricity. If an external voltage is applied across parts of die body, a current will flow which could result in shock, bums, paralysis, or death. The voltages needed to produce enough current to cause damage are not very high, but the damage depends on many factors such as where the current flows through the body, how effective the contact with the external voltage is, and so forth.
The high voltages on the primary side of welding equipment are the most hazardous, but the open circuit voltages on the secondary side of welding equipment, although limited for safety reasons, may still cause a serious shock under some conditions. Some types of equipment, such as plasma, may employ very high voltages.
In the majority of electrical circuits one part of die circuit is connected to the ground. For example, the white, “neutral” wire entering your house is connected to the ground. The red and black wires are the “hot” or Ive wires and are not connected to the ground (Fug. 7)
When one part of an electrical circuit is connected to die ground, it is only necessary for the body to touch one live conductor for a current to flow through the body and cause a shock. The current can return through the ground (Fig. 8). Anything that increases the electrical contact with the ground increases the ride of shock. For example, standing in water or working with wet hands.
Action in the event of shock
There may be secondary hazards associated with electric shocks even when the shock is small and does not cause any direct damage. A sudden jolt could cause die worker to slip andfall, possibly from a high place, or cause some other injury to himself.
If a workmate suffers an electrical shock, these are some of the actions to take:
Do not try and pull the victim from a live contact (unless there is no alternative).
Disconnect and turn off thepowerfirst thenremove die victim from contact
If the rescuer must reseat to pulling a victim from a live contact, he must insulate himself with gloves or similar protection.
If die victim is not breathing give artificial respiration. If the victim’s heart has stopped and if you have been trained, give CPR (cardiopulmonary resuscitation).
Call for help and call a physician.
Keep die victim horizontal and warm
Avoiding electrical hazards
Do not undertake work for which you have not been trained and are not qualified to do. Any electrical work, including installing plugs and outlets, must be done by a qualified electrician.
The high voltage input cable should be kept short and be protected at all times. Do not, for example, lay steel on it or drive a fork lift over it Before plugging or unplugging the high voltage input cable, turn the disconnect switch off. When turning the disconnect switch to “on stand to one side.
Correct electrical connections
Ensure that the welding equipment is correctly connected. One cable from the welding machine is connected to the electrode holder. The current from the power source flows through this cable to the arc then through the work piece and returns to the welding machine through the work lead. The work lead is not the ground lead. It is there to complete the electric circuit The work piece may be connected to a metal table or something similar which is in turn connected via the work lead to the welding machine. Fig. 9 shows the electrical connections for arc welding.
It is essential that die work lead make a good electrical contact with the work piece. If them is a bad connection, the current will try to find another path back to the power source through the grounding system, possibly causing damage. Check that there is no paint or grease preventing a good connection.
In some cases the welding current may be allowed to return through a metal structure such as a pipeline. This is not allowed if the pipe carries gases or flammable liquids. Neither must the current be carried across threaded, flanged, bolted, or caulked joints.
Never allow welding current to be carried by cranes, hoists, wire ropes, elevator structures or similar devices, and ensure cables are located where they cannot be physically damaged.
The flames of power sources, control panels, etc., must be connected to an approved ground. The work piece, too, must be separately grounded, preferably at the work piece itself but alternately at the welding machine. Grounding of the work piece prevents it becoming “live” in the event of a fault in the machine transferring high primary voltages to the secondary side. Work piece grounding also prevents the electrode voltage—relative to ground— “floating” above 80 V under open circuit conditions. If the work piece is grounded at the machine by a wire to the grounded enclosure, the wire must be smaller than the ground wire (Fig. 10).
Ensure that all cables are of the correct size to carry tie current This applies to both the welding cable and tie work lead- Under size cables could cause overheating and ignite a fire. The size of cable depends on the duty cycle which is the proportion of time that the current is actually flowing and is defined as the number of minutes that current flows for every ten minute period. Table 3 gives the recommended size for duty cycles up to 60%—typical for manual welding.
Long cables must be larger than short cables, but excessively long cables should be avoided. Use the shortest cable that is practicable. Do not wind the cable around your body (Fig. 11). Keep electrical connections tight, clean, and dry so they do not heat up or cause sparks.
Do not use any water cooled equipment or welding guns if any leaks exist To prevent condensation on cold water hoses from running into electrical equipment, place a loop in the hose (Fig. 12)
With automatic welding equipment the welding current is conducted through the electrode wire. The spool of wire is therefore “live” while the arc is burning. It is particularly important to remember this where the wire is fed long distances. For example, wire from a large pay-off pack may be fed over pulleys long distances to a robot In most equipment the welding current is only turned on by a contactor when the wire is being fed and the arc can bum. In some equipment, such as voltage sensing wire feeders used without contactors, the wire and spool can be “live” without the arc burning or the wire being fed. Under these conditions the operator is exposed to the full open circuit voltage (usually 80 V) of the power source. This hazard can be reduced by installing separate contactors.
Radiation is a way in which energy can be transferred from one location to another in the form of electromagnetic waves. The different types of radiation are distinguished by their wavelength or frequency as shown in Fig. 13. Radiation can pose a number of hazards which again depend on the wavelength and also on the intensity.
Types of radiation
Radiation may be classed as either ionizing or non-ionizing. The ionizing radiation has a short wavelength and can damage living cells. It can cause serious short term and long term health effects and can be fatal in sufficient doses. X-rays and gamma rays used in the radiography of welds are of the ionizing type and special safety precautions must been taken when using them. These must only be used by specially trained people. The warning symbol for this type of radiation is shown in Fig. 14. Ionizing radiation (X-rays) can also be emitted with certain welding processes such as electron beam welding.
The non-ionizing radiation emitted by welding arcs includes visible, ultraviolet, and infrared light (Fig. 15). The hazards from non-ionizing radiation encountered with the common welding processes are mainly bums, skin damage, and eye damage. While skin damage is mainly the result of ultraviolet radiation, eye damage can occur from ultraviolet, visible, and infrared radiation.