TB Electrical Hazards Continued. Flashcards
Overhead Transformers - Pole-mounted transformers are the most ___ distribution transformer.
common
Overhead Transformers -
They are installed on the 4.8kv circuits to step the voltage down to ___ volts for most residential consumers.
120/240
Transformers for subsurface electrical are mounted above ground on concrete bases called ____.
pad-mounted transformers
Pad-mounted transformers :
These large boxes are connected to ____ circuits and are located in parking lots of small and medium size businesses or in the front yard of some residences.
4.8kv
The conductors are materials that allow an electric current to flow through them ___.
easily.
Insulators are appliances which will ___ the flow of electricity and provides support to the conductor. They are most commonly made of glass or porcelain.
prevent
The most effective methods of identifying different voltages are:
1. ___ signs on the cross arms.
High voltage
The most effective methods of identifying different voltages are:
2. The size and shape of ____; remember, the ___ at the top of poles will appear smaller than they really are.
insulators
The most effective methods of identifying different voltages are:
3. The distance between ___; the higher the voltage, the greater the distance between _____.
conductors
Common Electrical Distribution Lines:
Primary wires = up to ____ volts of electricity
21,000
Common Electrical Distribution Lines:
Secondary wires = up to ____ volts of electricity
240
Common Electrical Distribution Lines:
Transformer = reduces ____ voltage to secondary voltage
Primary
Common Electrical Distribution Lines:
Electric Service = to house up to ___ volts of electricity
240
Common Electrical Distribution Lines:
Lowest lines =
Phone and Cable service
___ of an amp of electricity going through the body for just ___ seconds is enough to cause death.
1/10 / two
The amount of internal current a person can withstand and still be able to control the muscles of the arm and hand can be less than _____.
10 milliamps (mA).
Currents above ____ can paralyze or “freeze” muscles.
10 mA
People have stopped breathing when shocked with currents from voltages as low as ___ .
49 volts
Usually, it takes about ___ of current to cause respiratory paralysis.
30 mA
Currents greater than ___ may cause ventricular fibrillation (very rapid, ineffective heartbeat).
75 mA
Heart paralysis occurs at ____, which means the heart does not pump at all. Tissue is burned with currents greater than 5 amps.
4 amps
At ___ volts, the current through the body may be as great as 4 amps, causing damage to internal organs such as the heart.
600
Dry skin may have a resistance of ___ ohms or more. Wet skin may have a resistance of only 1,000 ohms.
100,000
The cutting of wires by firefighters must be confined to ____ wires.
low-voltage
Voltage Gradient: Is a ____ created when a energized wire is in contact with the earth.
decreasing current
Touch Potential: Occurs by contacting a ____ source. Touch potential commonly occurs when a vehicle, fence, or other conductor is in contact with a live conductor such as a downed wire.
live or energized
Step potential: Occurs when responders or victims create a ______ as they walk over or across a voltage gradient created by an electrical source, such as a downed wire.
circuit with their feet
Even overhead communication cable normally found on the lowest level of a power pole can be energized with up to ___.
50 volts
Spot apparatus and have responding personnel maintain at least one span (____) from the affected wire or pole.
the distance between two poles
For optimum safety, remember the distance between ___ poles will provide the best margin of safety.
two undamaged
Pad-mounted fires should be treated the same as overhead transformers by____, protect exposures and keep people away from the area.
letting them burn
Overhead Transformers :
Applying water should be ___ as it is not effective and it can cause adjacent wires to fall.
avoided
Streetlights can be fed from conductors carrying ___ volts or more.
120-6150
Utilize a ___ stream. The air spaces between the drops of water in the stream limit electrical conductance.
fog
Utilize the 30/33/100 Rule for using hose streams around high voltage:
The fog spray should be set at a _____ fog pattern. Straight streams or foam should not be used on high voltage sources.
30-degree
Utilize the 30/33/100 Rule for using hose streams around high voltage:
Firefighters applying water should maintain a distance of at least ____ from the energized source.
33 feet
Utilize the 30/33/100 Rule for using hose streams around high voltage:
Ensure a minimum of ___. is pumped to the nozzle. A strong stream will reduce conductivity.
100 psi
Occupants trapped : The vehicle should be driven clear of the wires by at least ____.
35 feet
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 ___ from the car.
small hops
There are two methods that can be used from removing oneself from an energized vehicle:
Jump from the vehicle without touching it and ___ the feet together.
shuffling
Maintain a safe distance from transmission towers: a minimum of ____ should be adhered to.
35 feet
Maintain clearance a minimum of ___ feet beyond the outermost wire of electrical transmission lines.
100
Operations Near Transmission Lines:
Never direct hose streams at ______.
high voltage wires
Operations Near Transmission Lines:
Keep hose streams ___ the height of individual operating it.
below
Operations Near Transmission Lines:
Never direct hose streams into heavy plumes of smoke within ___ of high-voltage wires
100 feet
With heavy smoke present, firefighters should be especially cognizant of remaining at least ___ from transmission lines and ___ from transmission towers.
100 feet / 35 feet
The explosive range for carbon monoxide (co) is____ percent.
12.5 to 74
Manhole covers often weigh 300 pounds and have been blown ___ into the air and a distance of ____.
75 feet / 125 feet.
Remember that the main fire hazard within electrical vaults lies in the ____ used in the transformers, which has a flash point below ____.
cooling oil / 300F
