Questions and Answers
What is the primary consideration when isolating an electrical problem in high-rise buildings?
Which hazard is presented by the UPS rooms in commercial occupancies?
When should the electricity be shut off at a residential fire?
What should thermal imaging cameras (TICs) be used for in residential occupancies?
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What indicates an open neutral or faulty ground in a residential occupancy?
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What is the potential danger of a wire with 'reel memory'?
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What happens after a recloser detects a fault and energizes the circuit?
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What should firefighters be cautious of when responding to manholes that are smoking or on fire?
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When will the TFD enter or attempt to fight fires in manholes?
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What is a critical piece of information about the Wilbur TAC stick?
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What is the primary risk when a downed, energized wire is in contact with the ground?
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What is the safest immediate action a responder should take if experiencing a tingling sensation near a downed wire?
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What configuration will typically be seen in the service wires entering a residential structure?
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What voltage will each of the two main service wires carry in a typical residential setup?
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Which scenario accurately describes step potential?
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What should firefighters do when investigating lines down?
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What is the purpose of establishing a 'Danger Zone'?
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How far should the 'Danger Zone' extend around damaged poles or wires?
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What action should be taken if an energized vehicle poses an imminent fire or explosion risk?
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What should be included in the report to PSO when responding to downed lines?
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Study Notes
Service Connections
- Service connections deliver power to customers through wires that enter the structure via weatherhead or conduit.
- Triplex wiring is common in residential structures, consisting of two 120-volt wires and one neutral wire.
Electrical Hazards
Ground Gradient
- A downed, energized wire in contact with the earth creates a current running to ground at the point of contact.
- A gradient of decreasing current emanates from the point of contact, potentially extending several feet.
- This creates a step potential hazard.
Step Potential
- Step potential occurs when responders create a circuit with their feet near a downed wire.
- This can cause a shock or even death if the voltage is great enough.
- To escape, bring both feet together and hop away from the downed wire location.
Reel Memory
- Electrical wire/cable can recoil in the direction of its original winding when unrolled from a spool.
- This can cause the wire to whip back towards the point of connection, especially if under extreme tension.
Recloser or Line Restorer (LR)
- A recloser recognizes a problem, waits a few seconds, and then energizes and tests the circuit.
- If the fault persists, the recloser repeats the process up to four times before requiring manual reset.
- Be aware of this when checking a downed wire using a TAC Stick.
Manholes
- Manholes are confined spaces where PSO splices wires.
- Beware of the cover becoming airborne due to an explosion.
- TFD will not enter or attempt to fight fires in manholes until PSO is on scene.
Wilbur TAC Stick
- The TAC stick manual is available on the Intranet.
- The manual covers the use and limitations of the TAC stick.
- Use the TAC stick when responding to downed lines.
Commercial Occupancies
- High-rise buildings may have electrical rooms on every floor.
- Isolating an electrical problem to a particular floor is crucial to avoid interrupting service to the entire building.
- Commercial occupancies may have UPS rooms with batteries that can deliver over 500 volts of direct current.
- These batteries pose an additional hazard of acid release.
Residential Occupancies
- When dealing with electricity at residential occupancies, consider the following:
- Shut off electricity to the house as soon as possible.
- TFD members will not engage in fire suppression or property conservation if energized electrical circuits or objects create an imminent life safety risk.
- Exercise extreme caution when using ground ladders.
- Be aware of signs of electrical issues, such as flickering lights, dimming lights, and shocks from appliances or plumbing.
- Thermal Imaging Cameras (TICs) can be useful in locating potential fires inside walls and identifying overheating wires and equipment.
Response to Downed Lines
- Attempting to locate a downed line/wire is extremely dangerous and has resulted in firefighter fatalities.
- Use extreme caution when carrying out these activities.
- Identify where the electricity will enter the structure and proceed to locate both ends of the downed wire.
- Always consider that there may be multiple downed wires or wires in contact with fences.
- Use the TAC stick to check gates before entering.
- Do not attempt to move downed electrical lines.
- Establish a guard around the scene and protect the public.
- Beware of covered overhead wires, as the covering is designed to protect the wire from weather or tree contact, not to protect responders.
- Establish a "Danger Zone" around damaged or downed electrical lines.
- The danger zone should extend at least one full wire span beyond damaged poles or wires.
- Instruct persons in energized vehicles to remain in the vehicle until the electrical energy is eliminated by PSO.
- In situations with an imminent life safety risk, instruct occupants to jump clear of the vehicle.
- Do not attempt to rescue persons in contact with energized lines or objects.
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Description
Learn about electrical service connections, triplex wiring, and ground gradient hazards, including downed energized wires and current flows.