Incidents involving electricity - PN 769

Question 1

Incidents involving electricity - PN 769

Electricity company premises include (5)

Answer 1

1. Power stations - Generally powered by a range of methods including fossil fuels such as coal, oil, gas or wood chip.
2. Sub-stations - Indoor or outdoor and may be present within another building such as an office block or large factory.
3. Distribution cables/equipment - Including cables mounted on poles, towers and pylons and those run underground, including pavement level electrical ducting (see appendix 2).
4. Fenced enclosures - containing transformers and other electrical distribution equipment. Some are continually staffed while others are monitored remotely (see appendix 3).
5. Wind turbines - These consist of a number of rotor blades attached to a horizontal or vertical axis shaft connected to a generator via a gear box housed inside a casing called a nacelle. As the rotor turns, wind energy is converted into electrical energy. This assembly is generally mounted high above the ground or exposed enough to harvest wind, dependant on site geography (see appendix 4).

Question 2

Incidents involving electricity - PN 769

At premises where a sub-station has been provided within a building, the transformer chamber/sub-station will be situated where?

The walls and floors separating it from the remainder of the building will have at least a [what] hour standard of fire resistance.

Answer 2

• Against an outer wall
• At least 4 hours

Question 3

Incidents involving electricity - PN 769

Irrespective of the voltage, ALL premises or equipment concerned with the generation and supply of electricity are potentially hazardous, and access to such equipment is restricted by what? (2)

Answer 3

1. Secured doors to switch rooms and transformer installations.
2. Fencing around installations and by placing equipment out of reach whether below ground or overhead (cable tunnels and pylons).

Question 4

Incidents involving electricity - PN 769

Smoke issuing from pavements or explosions in pavements can often involve pavement level electrical ducting.

How should crews deal with them?

Answer 4

Under no circumstances should crews seek to lift covers or further expose a pavement level cable system to extinguish the fire, unless the authorised person has confirmed that power has been isolated and any residual current has been discharged.

(leave, await authority, cover surrounding risks)

Question 5

Incidents involving electricity - PN 769

The following list outlines the specific hazards related to electricity (6)

Answer 5

1. Trip hazards
2. Hazardous gases or liquid
3. Electric shock
4. Explosion
5. Fire

THEEF

Question 6

Incidents involving electricity - PN 769

Electric shock is one of the main hazards associated with incidents involving electricity.

In what ways can this present problems (7)

Answer 6

1. Water. The application of water or foam directly onto live apparatus, equipment and appliances.
2. Touching. Touching live or damaged apparatus, equipment and appliances.
3. Heat/Smoke. When high voltage equipment, including overhead transmission lines, comes into contact with heat or smoke, ionisation of the air surrounding the conductor may occur. This increases the conductivity of air and will allow electricity to arc from the cables to earth or to adjacent structures, trees or fire brigade equipment.
4. Illegal. Illegal activity and overloading of electrical supply equipment. The safety of electrical supply equipment can be compromised by the overloading of electrical circuits, illegal bypassing of electricity meters and the illegal access to electricity.
5. Residual charge. Switching off the current to a high or low voltage installation, such as a cable, transformer or switch-gear does not necessarily render it safe, as a residual charge of electricity may be present in the apparatus. This residual charge may be sufficiently powerful to cause electrocution and needs to be made safe by an ‘authorised person’. If this equipment is damaged by fire and the supply to it is isolated, the risk is considerably reduced; this may allow firefighting and rescue operations to commence.
6. Standing. Standing in water, oil or other fluids or wearing wet PPE which is exposed to live electricity.
7. Theft. The theft of electrical components including earth straps may render parts of the site live, which would otherwise be assumed to be safe; this may include metal gates and fences.

WTHIRST

Question 7

Incidents involving electricity - PN 769

Fire is one of the main hazards with incidents involving electricity. If a fire situation is present what four hazards should be considered?

Answer 7

1. Large quantities of fuel may be stored within power generating stations. Hazardous substances such as methanol, propane, hydrogen, methane, chlorine and oxygen may also be found.
2. Oil filled transformers and switchgear can fail without warning and may pose a risk of explosion.
3. Insulating materials paper, oil or plastics may create a large amount of toxic and irritant smoke.
4. Gearbox oils may be present in relatively large quantities in the nacelle of the turbine. These oils are generally combustible and may present a risk of burning oil dropping inside or outside of the tower if ignited during a fire.

Question 8

Incidents involving electricity - PN 769

Explosion – Short circuiting and associated violent electrical arcing can cause an explosion in pavement level electrical ducting. What could crews potentially encounter?

Answer 8

These explosions can be violent enough to damage pavements and lift inspection covers, scattering debris over a significant area.

Also, other inspection covers in the same system can be affected.

Be aware of glass buildings.

Question 9

Incidents involving electricity - PN 769

Hazardous gases/liquids are one of the main hazards associated with incidents involving electricity.

In what ways can this present problems (2)

Answer 9

1. Some transformers and switchgear are protected by fixed installations which when operated, will fill compartments with carbon dioxide, sulphur hexafluoride or vaporising liquid, this may cause asphyxiation.
2. Battery acids are present in some wind turbines and usually consist of lead acid batteries similar to those found in cars. Battery acid may cause burns on contact with skin or eyes and may generate hydrogen during charging.

Question 10

Incidents involving electricity - PN 769

Trip hazards are one of the main hazards associated with incidents involving electricity.

In what ways can this present problems (4)

Answer 10

(a) Uneven or broken concrete covers on cable ducting.
(b) Uneven ground; open excavations; rubber mats in enclosed substations.
(c) Grease and oil, present in wind turbines, are used to minimise the level of friction and ensure smooth running of the turbine. Leaks are common and surfaces may be slippery or contaminated.
(d) Sumps and wells.

Question 11

Incidents involving electricity - PN 769

Insulating materials are one of the main hazards associated with incidents involving electricity.

In what ways can this present problems (3)

Answer 11

(a) PVC insulation: When involved in fire will produce large volumes of toxic and irritant smoke which will contain hydrogen-chloride gas.
(b) Polychlorinated Biphenyls (PCBs): PCBs, which are used in some transformers and other electrical equipment as an insulating liquid, are highly toxic and have harmful environmental effects if released, as they are not biodegradable. Some, but not all, transformers are labelled to indicate if they contain PCBs.
(c) Sulphur Hexafluoride (SF6): This gas is used as an insulating and interrupting medium in many types of electrical apparatus. It is heavier than air and will not disperse easily and can act as an asphyxiate in confined or low lying areas. BA and full fire kit should be worn when encountering SF6, and in the event of it being involved in a fire or other reaction, the advice of a hazardous materials and environmental protection officer (HMEPO) or scientific adviser should be sought since hazardous breakdown products may be present in the form of a gas or powder. This powder may contaminate the immediate area.

Question 12

Incidents involving electricity - PN 769

Attendance to incidents involving electricity should be made to where?

Answer 12

Attendance should be made to the main entrance to the premises or site, unless a previously agreed RVP has been identified during the pre-planning phase or the fire situation dictates this to be inappropriate.

Question 13

Incidents involving electricity - PN 769

The commander of the first appliance in attendance is to locate the ‘responsible person’ where available, and gather all relevant information to formulate a firefighting/rescue plan.

Explain the specifics for:

• Power Stations
• Overhead cables
• Substations
• Fire and explosions in pavement level ducting
• Wind turbine sites

Answer 13

(a) At power stations liaise with site personnel and comply with site specific or operational contingency plans.
(b) Overhead cables and pylons contact National Grid and request urgent attendance of authorised person.
(c) At a substation or part of the distribution network (EG - London Power Networks PLC/EDF Energy/Scottish Power) request urgent attendance of authorised person.
(d) Fire and explosions in pavement level ducting. Request the immediate attendance of the authorised person.
(e) At wind turbine sites the IC should liaise with onsite personnel and request the isolation of any power supplies to the wind turbine and have it confirmed that the blades have been “locked out” prior to taking any offensive action. Locking the blades in position does not remove the electrical risk posed by the turbine.

Question 14

Incidents involving electricity - PN 769

How should crews respond to warning signs or areas which have warning signs restricting access?

Answer 14

Wait until the responsible or authorised person is in attendance

Question 15

Incidents involving electricity - PN 769

If any high voltage equipment is identified as being involved, the relevant authorised person must be requested to attend. When requesting the attendance of the authorised person the IC must include what information?

Answer 15

• Info gathered from identification signs and plates
• Where appropriate advise them of any RVPs or access restrictions.
• The IC should include the areas affected and where known, the involvement of electrical apparatus.

Question 16

Incidents involving electricity - PN 769

The attendance time for the authorised person may take up to how long?

What hours of the day can the authorised person be deemed to be available?

Answer 16

The attendance time for the authorised person may take up to 2 hours.

The authorised person is available on a 24/7 basis. They will be carrying relevant identification and should liaise with the IC upon their arrival.

Question 17

Incidents involving electricity - PN 769

ICs must consider the effect of isolating power supplies in premises where…?

(3)

Answer 17

1. Where there are machine processes.
2. Where the absence of electrical supplies will affect occupants’ safety or welfare, or
3. Where there may be an adverse impact on business continuity.

Question 18

Incidents involving electricity - PN 769

In some instances, after all reasonable efforts have been made the authorised person may not be able to confirm all electrical supplies are isolated, without entering the compartment and testing the apparatus.

1. What if there is any possibility that high voltage supplies may be present?
2. What if it is confirmed the residual electrical supply is of low voltage?

Answer 18

1. If there is any possibility that high voltage supplies may be present no entry into the risk area should be made.
2. If it is confirmed the residual electrical supply is of low voltage then action can be taken, provided appropriate controls are put in place.

Question 19

Incidents involving electricity - PN 769

Substations sited within buildings will be situated against an outside wall and are constructed to provide [?] hours fire protection.

Answer 19

4 hours

Question 20

Incidents involving electricity - PN 769

Ladders and aerial appliances should not be used at external substations without what?

Answer 20

An assurance from the authorised person that it is safe to do so.

Question 21

Incidents involving electricity - PN 769

What important factor regarding extinguishing media, should be remembered when dealing with incidents involving delicate and complex apparatus such as that found in switchboards in generating stations, substations, telephone exchanges, or other electronic equipment such as computers.

Answer 21

That carbon dioxide or vaporising liquids do not damage electrical equipment.

Question 22

Incidents involving electricity - PN 769

List 2 scenarios where guidance must be sought from the authorised person before working near overhead power lines.

+

What can the authorised person help with.

Answer 22

1. Any No tower, structure or pole should be not be climbed without authorisation from an ‘authorised person’ of the relevant electricity company.
2. If it is necessary to use ladders or aerial appliances in close proximity to overhead power cables, guidance must be sought from the authorised person, and any equipment should be at least 10 metres from them. Attention should be paid to prevailing weather conditions as these will affect the movement of cables and visibility

+

The authorised person should also give an indication of the dangers and minimum distances necessary for safety.

Question 23

Incidents involving electricity - PN 769

What SSOW should be implemented to ensure the appropriate proximity to electrical apparatus is maintained?

Answer 23

Safety officers must be appointed to continually inform crews of their proximity to electrical apparatus, ensuring that constant communications are maintained with equipment/aerial operators during any movement/manoeuvring

Question 24

Incidents involving electricity - PN 769

In the case of high voltage overhead power lines there is the possibility of ‘arcing’ from a conductor to earth/ground or adjacent structures, trees or fire brigade equipment when there is dense smoke or flames rising close to the conductors and which may be affected by the prevailing weather conditions.

When working in these circumstances, firefighters should avoid positioning themselves or their equipment within a ‘corridor’ [how many] metres either side of the overhead power line (measured along the ground)?

Answer 24

10 metres either side of the overhead power line

Question 25

Incidents involving electricity - PN 769

Wind turbines

Any fire involving the nacelle or at a height will require the setting up of safety cordons, the size of which will depend on the height of the wind turbine.

What diameter cordon is usually recommended as a starting point?

Answer 25

300 metres

Question 26

Incidents involving electricity - PN 769

1. What does UPS stand for?

(not the delivery company!)

2. What are they?

Answer 26

1. Uninterruptible power supplies
2. Auxiliary means to provide electrical power in the event that the national grid/energy provider fails to maintain a constant supply. (Generators or battery banks)

Question 27

Incidents involving electricity - PN 769

Prior to attempting rescue or retrieval of persons from contact with electrical apparatus, the supply must be shut down.

Under what circumstances can LFB crews isolate the supply?

Answer 27

If the voltage is known to be 3300V or less, LFB electrical gloves will provide adequate protection.

Question 28

Incidents involving electricity - PN 769

Should a person be seen lying on top of a transformer, switch, or, anywhere else above ground level, can crews effect a rescue?

Answer 28

Crews must NOT be touched until word is received from an ‘authorised person’ of the Electricity Authority that it is safe for rescue work to be carried out.

Question 29

Incidents involving electricity - PN 769

After completion of the incident, the IC will assist other agencies where applicable.

The incident will be handed over to who?

Answer 29

The occupier, relevant authority and/or Police Service.

Question 30

Incidents involving electricity - PN 769

High voltage - greater than ?

Answer 30

1000 volts ac (or 1500 volts DC).

Question 31

Incidents involving electricity - PN 769

Low voltage - Less than ?

Answer 31

1000 volts ac (or 1500 volts DC)

Question 32

Incidents involving electricity - PN 769

Overhead cables

if crossing under overhead lines with ladders or tall equipment how should the equipment be carried?

Answer 32

The equipment should be kept horizontal and as near to the ground as possible.

Question 33

Incidents involving electricity - PN 769

Overhead cables

When carrying out a rescue in the vicinity of overhead lines, substations and other electrical equipment belonging to the electricity supply industry, what is the minimum safe approach distance?

Answer 33

5 metres

Question 34

Incidents involving electricity - PN 769

Overhead cables

When using ladders/aerial appliances or tall equipment (no hose), what is the minimum safe approach distance?

Answer 34

10 metres

(20 metres in training scenarios)

Question 35

Incidents involving electricity - PN 769

Overhead cables

In dense smoke or if flames are approaching the conductor, what is the minimum safe approach distance?

Answer 35

10 metre corridor

Question 36

Incidents involving electricity - PN 769

Overhead cables

When using hand-held jets what is the minimum safe approach distance?

Answer 36

20 metre corridor

Question 37

Incidents involving electricity - PN 769

Overhead cables

When using monitors (ground or aerial) what is the minimum safe approach distance?

Answer 37

30 metre corridor

Question 38

Incidents involving electricity - PN 769

Overhead cables

PTO for a table of the safe working distances

Answer 38