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Questions and Answers
The widespread use of electric power has resulted in many injuries and deaths due to exposure to ______
electricity
Many factors influence the severity of electrical ______
injuries
Contact with low voltages can also be ______
fatal
Moisture on the skin decreases the body’s resistance and increases the severity of the ______
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Partial insulation by dry clothing lessens the ______
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Electrocution at heights may result in a fall that can further injure the ______
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Electricity is generated by ______ plants
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This voltage is stepped up for efficient transmission over long distances to substations near the ______ centres
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Transmission lines operate between 69,000 volts and ______ volts
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Chapter 4 of the Western Canada Mine Rescue Manual focuses on ______ Hazards
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People, who place themselves between any two energized conductors, or any energized conductor and ground, will become part of an electrical circuit that can kill or cause serious ______.
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Current passing through the heart or brain is more life-threatening than current passing through the ______.
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Slight tingling sensation is experienced at a current level of ______.
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Painful shock, begin to lose muscular control at a current level of ______.
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Extreme pain, respiratory arrest, severe muscular contractions occur at a current level of ______.
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Ventricular fibrillation and muscular contraction begins to occur at a current level of ______.
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Cardiac arrest, internal organ damage, and severe burns occur at a current level of ______.
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Electricity is safe in normal operating conditions. However, hazards are created when electrical equipment or wires have become faulty due to: Wear or other ______.
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An arc flash hazard can exist when energized electrical conductors or circuit parts are exposed or are within equipment in a guarded or enclosed ______.
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Contact with overhead power lines is a major cause of fatalities for ______.
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Electricity can travel from a power line to a worker touching any part of the ______ or the load.
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Haul Trucks and Other Heavy Equipment Tires can ______ during or after contact with power lines / lightning.
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If a vehicle contacts overhead power lines there may be a massive electrical current flowing through the vehicle and its ______: This can cause the tires to explode on contact or could cause the tires to start burning inside.
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Rescue teams must consider their approach angle, safe distances, and the size of the ______.
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This creates a build-up of gases and heat which could cause the tire to explode at a later time, even as much as 24 hours after the ______.
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The resulting explosion could potentially injure persons in the proximity with flying ______.
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The vehicle should be isolated for a period of time at a safe distance to avoid ______.
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Ground Engagement Tools (excavators, dozers, graders, etc.) Buried power and communication lines pose a hazard to operators of equipment used during trenching and excavation ______.
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Operators need to be aware of the hazards posed by penetration of energized power lines and take positive steps to eliminate the hazard before ______.
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Always assume that all electrical wires and equipment are energized until proven ______.
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At the substations, voltage is reduced and power is sent through distribution lines to industrial, commercial, and residential customers. These lines operate between 5,000 V and 25,000 V. Some mines, especially those in more remote locations, have their own on-site power-generating capabilities. These facilities present unique circumstances during emergencies. CONCEPTS AND DEFINITIONS Voltage is the difference in electrical potential between two points in an electrical field. It is the force that causes the flow of electricity, and it is measured in ______ (V).
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Because mines require high voltages, kilovolts (kV, 1 kV = 1,000 V) are often used to express the difference in electrical potential. Current is a flow of electrical charge. It can be compared to the rate of water in a pipe. Current is typically measured in ______ (A). (1 ampere = 1000 milliamperes (mA)).
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 Alternating Current (AC) refers to when a current in a circuit reverses polarity or changes direction in current flow 60 times per second (60 Hz).  Direct Current (DC) refers to a current flowing only from positive to negative. Resistance is similar to the effect of friction on the flow of water in a pipe. Water flows more freely in a large pipe than in a small one, and different materials have different resistances to the flow of electricity. Resistance is measured in ______ (Ω).
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Grounding is the process of mechanically connecting isolated wires and equipment to the earth, with sufficient capacity to carry the fault current and to ensure the wires and equipment remain at the same potential (same voltage) as the earth (ground). Bonding is the process of joining together two conductors that do not carry currents. These may be two wires, a wire and a pipe, or these may be two pieces of equipment. Bonding is done by connecting all the metal parts that are not supposed to be carrying current during normal operations, thereby bringing them to the same electrical potential. Grounding is still required after bonding as bonding itself does not protect anything. Insulators are materials of high resistance that conduct electricity in such small quantities that it cannot normally be detected. Examples of insulators include glass, ceramic, and ______.
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Conductors are materials of low resistance that conduct electricity in large amounts. Examples of conductors include copper, aluminum, iron, salt water (brine), and most other metals. Semiconductors are materials that have a value of resistance between those of insulators and conductors. Examples of semiconductors include wood, earth, and ______ tires.
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An electrical arc is a sudden release of electrical energy bridging a gap between two conductors. An arc can be extremely hot. Arcing is usually associated with a short circuit, a current interruption at a switch point, or loose ______.
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Loose connections and overloaded electrical conductors or motors cause ______. Exceeding the amount of current that conductors and equipment are designed to carry is dangerous and can be avoided by using properly-sized overload and short-circuit protection devices.
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Most electrically caused fires originate in equipment operating below 750 V. In the electrical industry, anything below 750 V is commonly referred to as low voltage or secondary voltage. Electricity can arc through the air to a person, tool, or other conductor if they get too close. All rescuers, tools, and equipment including aerial devices and extension ladders must maintain a minimum distance known as the safe limit of approach. Canadian Electrical Code’s Safe Limits of Approach Voltage of Live Power Minimum Distance 0–750 V 1 M (3 ft) 750–150,000 V 3 M (10 ft) 150,000–250,000 V 4.5 M (15 ft) Greater Than 250,000 V 6 M (20 ft) Voltage Gradient on the Ground Because electricity always seeks the path with the least resistance to the ground, electrical systems use conductive grounding rods to ensure that any stray current is returned to earth safely. These rods are typically driven 2.5 m (8 ft) or more into the ground to ensure good contact with the ground. However, if 4-3 electricity is released onto the surface, such as when a 'live' wire lies on the ground, the electricity will fan out from the point of contact. During a fault to the ground, there is a rippling effect that can be likened to dropping a pebble into calm water. In the pool of water, the wave created at the point of contact gets smaller as it spreads outward. Similarly, in a 'pool' of electricity, the energy is at full system voltage at the point of ground contact, but as you move away from the contact point, the voltage drops progressively. This effect is known as ______ gradient.
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The ground gradient, or voltage drop, creates two problems: step potential and touch potential. Assume that a live downed wire is touching the ground and has created a pool of electricity. If you stand with one foot near the point of ground contact (at x voltage) and your other foot a step away (at y voltage), the difference in voltage will cause electricity to flow through your body. This effect is referred to as ______ potential.
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Similarly, electricity will flow through a body if it touches an energized source with the hands, but the feet are at some distance from the source. The difference in potential voltage in this case is referred to as ______ potential.
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