Week 4 Electrical Hazards and Controls PDF

# Electrical Hazards and Controls ## Module Summary - Upon completion of this module, you should be able to: - **Remember:** Identify the dangers associated with electricity. - **Understand:** Describe the three main types of electrical hazards: electrical shock, arcing and electrical fires...

# Electrical Hazards and Controls ## Module Summary - Upon completion of this module, you should be able to: - **Remember:** Identify the dangers associated with electricity. - **Understand:** Describe the three main types of electrical hazards: electrical shock, arcing and electrical fires. - **Differentiate:** Explain the hierarchy of controls as it applies to electrical hazards. ## Topic 1: Introduction to Electrical Hazards and Controls - We depend on electricity in our lives. - It is important that engineers understand the dangers of working with electricity. - As future engineers, you will be responsible for ensuring the safety of the people using your products and designs. - You need to understand the dangers associated with electricity, recognize the main types of electrical hazards and determine the appropriate hierarchy of controls for each of these hazards. ## Topic 2: Dangers of Electricity ### The Cost of Electrical Accidents - Electrical accidents cost millions of dollars in property damage, not to mention the cost in injuries and loss of life. - The following statistics give you an idea of the cost of electrical-related accidents: - In one year there were 53,589 electricity-related fires reported in Canada, resulting in 304 deaths; 2,547 injuries; and $1.49 billion in property losses. - In Ontario, electricity-related injuries cost an average $1.3 million annually. - In the United States, there are 43,900 electrical-related house fires each year, resulting in 438 deaths; 1,430 injuries; and costing $1.47 billion in property damages. - Human error or activity is the major cause of electrical incidents. - Based on a 10-year statistic, for every 15 non-critical electrical injuries, i.e. injuries resulting from electrical incidents, there is one fatality. The injury-to-fatality ratio of other occupational lost-time injuries is 755 to 1. This statistic suggests that the severity of an injury from an electrical incident is much greater than that from many other types of incidents. ### Electrical Incidents - Electrical incidents result in high numbers of fatalities and injuries as well as significant property loss in Canada and the United States every year. - The following two examples illustrate how easily serious electrical incidents can occur if we are not aware of the potential hazards around us: - **Incident 1:** A precast concrete company was making a delivery with a boom truck at a road rebuilding site. A worker helped guide the load into place by grabbing one of the legs of the sling suspending the load. The wire rope contacted an overhead powerline. The worker received a severe shock and fell to the ground in convulsions. - Investigators determined that the following human factors may have contributed to the incident: - The company had not designated an area for unloading. - A signaler was not used to guide the process and alert workers of any hazards. - The boom truck operator's view might have been obstructed by the worker standing in front of him on the flatbed of the truck. - **Incident 2:** Electricians were connecting temporary lighting cables to the electrical panel on a construction site. An apprentice entered the panel to pull up a cable and hook it into the power panel. The apprentice came into contact with the exposed terminals and was fatally injured. The company was fined $300,000 for failing to ensure the workplace was safe and failing to provide adequate supervision. - Investigators determined that the following human factors contributed to the incident: - The panel had been left energized. - The apprentice had not been wearing any personal protective equipment. - Workers had not followed safety policies. - The contractor had not conducted a hazard assessment prior to performing the work. ## Topic 3: Electrical Hazards ### The Three Main Types of Electrical Hazards - You should now have an appreciation of how common electrical incidents are and the damage they can cause. - By learning to recognize electrical hazards and acting to control these hazards, we can lessen the chances of an incident occurring. - The three main types of electrical hazards are: - Electrical shock. - Arcing incidents. - Electrical fires. ### Electrical Shock - An electric shock occurs when electricity enters the human body in an attempt to complete a circuit. - Both low and high voltage currents can electrocute. - Even mild electrical shock can cause considerable damage to muscle strength, memory and even an individual's mental health. - Electrical shock can occur through: - **Direct contact:** A person comes in direct contact with an energized conductor or surface. - **Step or touch potential:** The difference in voltage between the feet of a person standing near an energized grounded object. - **Reverse polarity:** The hot and neutral wire connections at the receptacle are reversed. ### Arcing Incidents - Arcing is defined as a flow of current through an insulating medium that is accompanied by light, heat and sound. - Lightning is an extreme example of an electrical arc. - In the workplace, arcing usually occurs when a tool makes contact with an energized piece of equipment, for example a screwdriver and a buss bar, or a loose nut and an energized part of an electrical panel. - The severity of an electrical arc incident depends on the energy, which is the amount of current released. This current is called incident energy. - The tremendous temperatures of an arc flash cause the explosive expansion of air and metal in the arc path known as an arc blast. - The temperature of an electric arc can reach as high as 20,000°C, a temperature four times as hot as the sun. - A person standing even several feet away from an arc can suffer severe burns. Because of the high temperatures of an arc, skin and clothing can ignite even if they do not come in contact with fire. - Arc flash can kill a person at a distance of 3 metres. - In cases where the arc temperature is very high, an arc blast converts metal from solid to vapour state. When this vapour is inhaled, it causes severe burns to the respiratory system. - Each year more than 2,000 people in the United States are admitted to burn centres with severe arc flash burns. ### Factors that Contribute to Arcing - Factors that contribute to the intensity of an arcing incident include: - The size of the transformer or incident energy. - The impedance of the transformer. - The transformer voltage and current. - The duration of a fault. - The distance from the origin of the electrical system. ### Electrical Fires - Electrical fires account for many of the deaths related to electrical incidents. - They result from the incorrect use or poor maintenance of electrical equipment rather than faulty equipment design. - They occur more often in homes rather than in commercial or industrial facilities. - Electrical fires are mainly caused by arcing and overheating. - Common causes of electrical fires:  - **Arcing:** Fires caused by arcing usually result from improper or damaged electrical terminations and/or failing conductors. - **Overheating because of wiring alterations:** The electrical wiring in many older buildings has been altered to meet the changing needs of its occupants. These alterations may not have been inspected by a licensed electrician to ensure the installation can handle the load. - **Over-fusing:** Over-fusing happens when a higher ampacity fuse is used to replace a lower ampacity fuse. Homeowners and building managers often over-fuse a branch circuit. - **Overheating of extension cords:** Extension cords or flexible cords are frequently misused, especially in older buildings where there are a limited number of outlets. ### Hierarchy of Controls for Electrical Hazards - There are five methods for controlling electrical risk, arranged in order of decreasing effectiveness. - **Elimination:** The most effective way to control hazards. If the hazard no longer exists, then the risk no longer exists. Eliminating a hazard ensures everyone and everything is safer. - **Inherent safety:** An inherently safer design is one that permanently eliminates or reduces hazards to avoid or reduce the consequences of incidents. A process can be made inherently safer using one of four inherently safer design principles: - Minimization: Reducing the amount of a hazard that is present. - Substitution: Replacing a hazard with a lesser hazard. - Moderation: Using a less hazardous form of a hazard. - Simplification: Operating around a hazard in as easy and direct a manner as possible. - **Engineering controls:** Systems added on to a process in order to prevent or mitigate a loss of containment. - **Administrative controls:** Controls that reduce risk by instructing how work must be done safely. - **Personal protective equipment:** Equipment that a worker wears to protect themselves from hazards. ## Application of Hierarchy of Controls to Electrical Hazards - Electrical hazards can be managed by applying the five levels of control: - **Elimination:** Processes can be modified to eliminate all high voltage requirements from equipment. - **Inherent safety:** Electrical power can be substituted with other sources of power. - **Engineering controls:** Using the correct fuse for a circuit is an example of an engineering control. - **Administrative controls:** An organization's policy prohibiting the use of extension cords and devices that increase the number of plug receptacles for a single outlet would be an administrative control. - **Personal Protective Equipment:** Insulated gloves, boots and protective clothing, such as a fuse puller, are all examples of personal protective equipment.