TB 8 Electrical Hazards Flashcards
TB 8 Electrical Hazards
electrical accidents in the United States account for over 700 deaths a year and OSHA statistics indicate that electrocution accounts for 12% of worker deaths annually. NIOSH statistics also document that over the last 20 years, electrocutions to first responders have resulted in more than 25 deaths in the fire service.
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TB 8 Electrical Hazards
The Los Angeles Fire Department (LAFD) resources respond to over 3000 electrocutions, wires down, and other electrical emergencies annually.
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TB 8 Electrical Hazards
AMPS- Current flow, or electron flow,
Current flows from points of high voltage to points of low voltage on the surface of a conductor and is measured in Amperes.
The flow of electricity maybe compared with the flow of
water through a fire hose. Quantity of electricity is expressed in Amperes (amps); conversely, water
is measured in gallon per minute (gpm).
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TB 8 Electrical Hazards
VOLTS- Voltage is the difference in electrical potential between two points in a circuit.
Electrical pressure is measured in volts, while the comparable term in water hydraulics would be pounds per square inch (psi).
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TB 8 Electrical Hazards
KILOVOLTS- The measure of 1000 volts.
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TB 8 Electrical Hazards
OHMS- Resistance determines how much current will flow through a component.
The resistance to a flow of water through a hose would be termed friction loss and would be measured in pounds per square inch.
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TB 8 Electrical Hazards
WATTS- Power is the amount of current times the voltage level at a given point measured in wattage or watts. (Watts = amps x volts.)
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TB 8 Electrical Hazards
Even overhead communication cable normally found on the lowest level of a power pole can be energized with up to ____ volts.
50
TB 8 Electrical Hazards
Streetlights can be fed from conductors carrying ___ - ___ volts or more.
120-6150
TB 8 Electrical Hazards
Watts = amps x volts
Amps = watts x volts
Volts = watts x amps
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TB 8 Electrical Hazards
Maintain a safe distance from transmission towers: a minimum of ___ feet should be adhered to.
35
TB 155
Maintain a 35’ distance from transmission LINES
Spot fires or low ground fires can be fought with hose lines if heavy smoke or flame is not within 100’ of the power lines
TB 8 Electrical Hazards
Maintain clearance a minimum of ___ feet beyond the outermost wire of electrical transmission lines.
100
TB 155
Maintain a 35’ distance from transmission LINES
Spot fires or low ground fires can be fought with hose lines if heavy smoke or flame is not within 100’ of the power lines
TB 8 Electrical Hazards
ELECTRICITY FIRE HYDRAULICS
Conductor = Hose
Current = Water
Voltage = Pressure
Amperes = Gallons per minute
Ohms = Friction Loss
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TB 8 Electrical Hazards
Getting electricity to the consumer can be broken down into three systems:
Generation,
Transmission
Distribution System.
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TB 8 Electrical Hazards
Transmission lines are used to carry high voltage electricity the long distances from generating plants to distribution stations.
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TB 8 Electrical Hazards
Voltages on transmission lines range from 69kv to over 1000kv. Most of the transmission lines coming into Los Angeles are ____ kv, but many lines are higher than that. All voltages above 69kv are referred to as transmission voltages.
230kv
TB 8 Electrical Hazards
Strings of insulators on transmission towers can range from ___ to ___ feet long depending on the voltage they are trying to hold back from contacting the towers that support them.
3 to 20
TB 8 Electrical Hazards
The component of the electric system that delivers electrical energy to the consumer or residence
consists of distribution stations and distribution lines.
This system works by stepping down the voltage while
proportionately stepping up the amps with transformers the same way the voltage was stepped up in the generation system at the beginning of the circuit.
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TB 8 Electrical Hazards
There are over 150 distribution stations where the electricity is received at ___kv and stepped down to ___ kv. This is the voltage known as primary circuit voltage. The ___kv primary lines run from a distribution station to the neighborhood that it feeds.
- 5
- 8
- 8
TB 8 Electrical Hazards
The LADWP has many consumers that are connected to the grid at high-voltage(any voltage 600 volts and over). The most common are large commercial or industrial consumers such as hospitals, malls, high-rise buildings, metro rail stations and large complexes, which are connected at 34.5kv.
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TB 8 Electrical Hazards
Transformers are designed to reduce the voltage in the system to a voltage usable by the consumer.
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TB 8 Electrical Hazards
HIGH-VOLTAGE CAPACITOR
A capacitor is a type of electronic component which passively acts as a form of conductor.
When a charge of opposing currents is run through the device then a field is generated in which energy is stored. This energy can then be tapped through various means, allowing it to run devices which require electricity to work.
High-voltage capacitors have been known to retain a deadly electrical charge even weeks after power has been removed from the circuit.
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TB 8 Electrical Hazards
Overhead Transformers - Pole-mounted transformers are the most common distribution transformer. They are installed on the ___kv circuits to step the voltage down to ___ volts for most residential consumers.
4.8kv
120/240
TB 8 Electrical Hazards
Pad-Mounted Transformers - Transformers for subsurface electrical are mounted above ground on
concrete bases called pad-mounted transformers. These large boxes are connected to 4.8kv circuits
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TB 8 Electrical Hazards
Conductors – The conductors are materials that allow an electric current to flow through them easily.
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TB 8 Electrical Hazards
Insulator – Insulators are appliances which will prevent the flow of electricity and provides support to the conductor. They are most commonly made of glass or porcelain.
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TB 8 Electrical Hazards
Service Connection – The wires that connect the customer or home to the secondary transformer and may be high or low voltage.
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TB 8 Electrical Hazards
The most effective methods of identifying different voltages are:
- High voltage signs on the cross arms.
- The size and shape of insulators; remember, the insulators at the top of poles will appear smaller than they really are.
- The distance between conductors; the higher the voltage, the greater the distance between conductors.
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TB 8 Electrical Hazards
Early defibrillation has consistently been shown to be
the single most important factor in the resuscitation of patients in cardiac arrest. The sooner after the cardiac arrest a patient is defibrillated the more likely the patient is to be resuscitated. For every minute that defibrillation is delayed, the patient sustains a 10% reduction in their chances for survival.
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TB 8 Electrical Hazards
The cutting of wires by firefighters must be confined to low-voltage wires. In an emergency when there is a need to cut high-voltage lines, call MFC and request LADWP personnel trained to handle high voltage. Wires on poles shall not be cut by firefighters unless there is an immediate life hazard, and then cutting must be confined to low voltage wires.
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TB 8 Electrical Hazards
Cut the closest conductor first. When cutting, do not touch another conductor or a ground. After cutters are in place, turn head to protect eyes from flash and sparks.
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TB 8 Electrical Hazards
Voltage Gradient: Is a decreasing current created when a energized wire is in contact with the earth. The ground soil becomes a conductor and will allow current to travel a distance from an energized source, such as a fallen wire. The current spreads out from point of the energized source like ripples in a pond. A person stepping into this ground gradient will receive an electrical shock.
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TB 8 Electrical Hazards
Touch Potential: Occurs by contacting a live or energized source. Touch potential commonly occurs when a vehicle, fence, or other conductor is in contact with a live conductor such as a downed wire.
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TB 8 Electrical Hazards
Step potential: Occurs when responders or victims create a circuit with their feet as they walk over or across a voltage gradient created by an electrical source, such as a downed wire.
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TB 8 Electrical Hazards
The apparatus is not insulated from the ground by its rubber tires and may be energized by live wires in the following ways:
- By touching an object that is in contact with a live conductor
- By direct contact with a live conductor
- By way of an extended aerial ladder touching a live conductor If there is any chance that the apparatus is in contact with a live conductor, and it is necessary to get off the apparatus, do not step off, get above the running board cable and jump off. If you are on the ground, make no attempt to get on an electrically charged apparatus.
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TB 8 Electrical Hazards
For voltages of 600 or more, Cal/OSHA and NFPA standards require that aerial ladders be operated
at a minimum clearance of ten (10) feet of power lines and electrical devices.
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TB 8 Electrical Hazards
Any metal part of an aerial ladder that touches high-voltage lines energizes the entire apparatus,
and the apparatus is then potentially deadly. The essential point is never providing a ground for an
electrical contact. The safest course of action for the operator is to touch nothing until the power is off. The operator is usually safe remaining at the controls. If the operator decides to jump clear, be sure not to touch any part of the equipment when it is electrically charged; this should be done in such a manner that contact is not made between the truck and the ground at the same time.
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TB 8 Electrical Hazards
If apparatus touches a high-voltage line, the operator should back the equipment away or lower the aerial to break contact with the power line.
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TB 8 Electrical Hazards
Spot apparatus and have responding personnel maintain at least one span (the distance between two poles) from the affected wire or pole. If the pole is damaged don’t count the damaged pole. For optimum safety, remember the distance between two undamaged poles will provide the best margin of safety.
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TB 8 Electrical Hazards
Although LAFD ladders are wood construction, they are still conductive.
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TB 8 Electrical Hazards
Falling conductors often create much sparking, after which the conductors appear deenergized. Circuit breakers in these systems are designed to kick out and then kick back in automatically. The circuits will be energized again unless there is a ground or short circuit. The fact that wires on the ground do not spark or sputter is no indication that they are dead.
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TB 8 Electrical Hazards
Sheared hydrants impacting high voltage lines
Unless a life hazard exists, notify and await arrival of LADWP personnel.
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TB 8 Electrical Hazards
Overhead transformers
Applying water should be avoided as it is not effective and it can cause adjacent wires to fall. Fire Department personnel should extinguish only after LADWP has de-energized the equipment.
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TB 8 Electrical Hazards
Pad mounted transformers
let them burn and protect exposures
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TB 8 Electrical Hazards
Utilize the 30/33/100 Rule for using hose streams around high voltage:
The fog spray should be set at a 30-degree fog pattern. Straight streams or foam should not be used on high voltage sources.
Firefighters applying water should maintain a distance of at least 33 feet from the energized source.
Ensure a minimum of 100 psi. is pumped to the nozzle.
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TB 8 Electrical Hazards
The clearly identified method to assure that fire personnel and other responders do not enter Life
Hazard Zones includes the use of a minimum of three (3) horizontal strands of barrier tape that state “Do Not Enter” or “Do Not Cross”.
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TB 8 Electrical Hazards
If the vehicle is on fire or is in a position where an exigent-life threatening situation exists such as dangling off a freeway overpass, the people inside should attempt to self extricate. There are two methods that can be used from removing oneself from an energized vehicle:
Jump or leap from the vehicle without touching it, keeping both feet together and taking small hops from the car.
Jump from the vehicle without touching it and shuffling the feet together.
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TB 8 Electrical Hazards
Make no attempt to extinguish fires involving above ground or underground electrical equipment until notified by the LADWP that the electrical current is turned off.
The smoke from an electrical vault or manhole fire is both toxic and potentially explosive because the fire burning inside is most likely conduit and the fact that the fire is burning underground results in the fire being oxygen-starved. Any spark from power tools can cause serious or even deadly hazards to rescuers.
The explosive range for carbon monoxide (co) is 12.5 to 74 percent.
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TB 8 Electrical Hazards
Manhole covers often weigh 300 pounds and have been blown 75 feet into the air and a distance of 125 feet.
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TB 8 Electrical Hazards
Do not reach over charged wires. Cut the closest conductor first.
Do not cut two or more triplex cables at the same time.
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TB 8 Electrical Hazards
Remember that the main fire hazard within electrical vaults lies in the cooling oil used in the transformers, which has a flash point below ____F.
300
TB 8 Electrical Hazards
Location of the cables in vault is no longer an indication of voltage. High-voltage cables, up to 230,000 volts, may be located close to the floor inside a conduit containing 200-psi oil pressure.
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TB 8 Electrical Hazards
____ of an amp of electricity going through the body for just two seconds is enough to cause death.
1/10
TB 8 Electrical Hazards
Extremely high voltage: voltages in excess of ____ volts. Usually transmission voltage.
60,000
TB 8 Electrical Hazards
High voltage: voltage from ___ volts up to ____ volts.
600 to 59,999 volts
TB 8 Electrical Hazards
Low Voltage: Usually below ___ volts.
600
TB 8 Electrical Hazards
what is the 30/33/100 rule
30 degree cone
33 feet away
100 PSI minimum to nozzle
TB 8 Electrical Hazards
Voltages on transmission lines range from ____ to over ____.
69kv to 1000kv
TB 8 Electrical Hazards
All voltages above ___kv are referred to as transmission voltages.
69kv
TB 8 Electrical Hazards
Each primary has an average of ___ consumers.
750
TB 8 Electrical Hazards
Heart paralysis occurs at 4 amps, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.
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TB 8 Electrical Hazards
Ultimately, the danger from electrical shock depends on the:
Amount of the shocking current through the body
Duration of the shocking current through the body
Path of the shocking current through the body
TB 8 Electrical Hazards
The clearly identified method to assure that fire personnel and other responders do not enter Life Hazard Zones includes the use of a minimum of ___ horizontal strands of barrier tape that state “Do Not Enter” or “Do Not Cross”.
3
TB 8 Electrical Hazards
A charge of static electricity capable of jumping ___ to ___ inches may build up in a person’s body when climbing a tower.
two or three
TB 8 Electrical Hazards
Water by nature is not a good conductor but there are factors that increase the conductivity of water: dissolved minerals and impurities in water.
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TB 8 Electrical Hazards
if there is a square manhole, which indicates a ______.
transformer vault
TB 8 Electrical Hazards
Location of the cables in vault is no longer an indication of voltage. High-voltage cables, up to 230,000 volts, may be located close to the floor inside a conduit containing 200-psi oil pressure.
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TB 8 Electrical Hazards
Underground lines can be found in conduits or ducts and are identified by warning signs labeled UG (underground). Electrical distribution lines placed directly in the ground are designated direct buried (DB).
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TB 8 Electrical Hazards
Dry skin may have a resistance of 100,000 ohms or more. Wet skin may have a resistance of only 1,000 ohms.
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