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Electrical Fire Safety- Guide for Electrical & safety engineers

Among different categories of fire, electrical fire is considered as one of the most common and hazardous. According to the U.S. Fire Administration, in 2014, short circuit is solely responsible for 6.3% nearly 24000 fire accidents. Among them 11% caused death of the subjects. Due to increasing frequency and casualties, electrical fire safety and protection is really being emphasized. This article focuses on electrical fire protection in substations.

1)   What is fire?

Fire is an oxidation process that happens very fast, so that light, heat and sound are released results in smoke, the toxic waste of fire’s leftovers.

2)   What is electrical fire?

Fires directly caused by the flow of electric current or by static electricity is called electrical fire. They are one of the important types of structure fires.

3)   Causes of fire due to Electricity

Physical mechanisms causing electrical fires, ranked according to importance.

Mechanism Importance
Poor Connections Most

 

 

 

 
Least

Arcing across a carbonized path
Arcing in air
Excessive thermal insulation
Overload
Ejection of hot particles
Dielectric breakdown in solid or liquid insulators
Miscellaneous phenomena

Causative factors for electrical distribution systems fires, according to CPSC study.

Factors Leading to fire Percent
Improper alterations 30.4
Improper initial installation 16.6
Deterioration due to aging 13.8
Improper use 12.7
Inadequate capacity 12.2
Faulty product 9.4
Unknown 5.5

4)   Types of fire

Following are the classes of fires categorized as follows:

Class A: SOLIDS such as paper, wood, plastic etc
Class B: FLAMMABLE LIQUIDS such as paraffin, petrol, oil etc
Class C: FLAMMABLE GASES such as propane, butane, methane etc
Class D: METALS such as Aluminium, magnesium, titanium etc
Class E: Fires involving ELECTRICAL APPARATUS
Class F: Cooking OIL & FAT etc

 5)   Possible Sources of electrical fire in Substation

Following are the possible causes of fire in substation:

  • Energized cables
  • Batteries
  • Surge arresters
  • Direct-stroke lightning
  • Grounding
  • Fault-sensing & interrupting devices
  • Metal -clad switchgear
  • Oil-filled reactors
  • Power capacitors
  • Diesel / Gasoline Engines
  • Fuel handling systems
  • Relay & Control Panels
  • Gas-insulated components
  • High pressure oil-filled cable pumping plants

6)   Fire Hazards:

Following are the types and origins of substation fires as reported by Major Utility 1971-1994 as:

Types and Origins of Fires Percentages
Oil-insulated circuit breakers 14.0
Current transformers 14.0
Power transformers 9.3
Hot work procedures (welding, cutting and grinding) 9.3
Potential transformers 7.8
Engine-driven generators 7.0
Arson 6.3
Smoking 6.0
Lightning 4.7
Flammable liquid storage or handling 3.1
Terrorism 1.6
Miscellaneous fires 15.8

 7)   Fire Protection Measures:

7.1      Manual system

To prevent a fi re that has already started from spreading, you must remove one or more of the three elements of fuel, oxygen and heat from the fire.

Electrical Fire safety chart which type of fire extinguisher used for which type of fire
electrical fire safety and protection chart

7.2      Passive Fire Suppression system

Passive fire protection measures shall be provided where the risk of fire spread is identified as too high.

Passive measures shall be adopted in preference to the provision of active systems.

7.3      Active fire suppression system

Active fire suppression systems shall be used where the risk of fire is too great or the consequences of fire are unmanageable.

Active fire suppression system options appropriate substations include:

  • Fixed automatic aqueous fire fighting systems;
  • Hydrant systems for fire fighting purposes;
  • Extinguishers for first aid fire fighting;
  • Gaseous suppression systems.
  • Foam inlets

7.4      Fire Alarm System

The primary purpose of fire alarm systems is to provide notification of fire alarm, supervisory, and trouble conditions. Its secondary purpose includes alert to occupants; summon aid; and to control fire safety functions.

Automatic detection systems shall be provided within substation switchrooms.

Oxygen masks, smoke detection and alarm systems shall be provided within substation buildings.

The air sampling systems shall have the following alarm levels.

  1. a) Stage 1 – Initial detection. Signal to SCADA system.
  2. b) Stage 2 – Alarm to SCADA System recommending investigation/ evacuation.
  3. c) Stage 3 – Full alarm. Operations centre evaluate alarm.
  4. d) Stage 4 – Intervention by brigade. The detection devices must be fully monitored for alarm and/or fault condition to ensure reliable service. The device should be able to transmit a fire alarm signal to emergency control center.
Fire extinguishers used for electrical fires must no increase the risk of electrocution to fire fighter.
Water based systems shall only be used within the fire area after the electrical systems is isolated and made safe.

7.5      Exits

An exit is that part of a means of egress that leads from the floor area it serves to a public thoroughfare or to an approved open space.

7.6      Emergency lightings

Emergency lighting ensures that exits, corridors and principal routes providing access to exits are illuminated in the event of loss of power.

Resource:

NFPA 72 (2002), Research on Electrical Fires- Fire Science & Technology Inc., IEEE 979 (1994), BC Hydro, Substation Design Guide- VESDA, Industrial Fire Safety Plan Guidelines, Substations Fire Protection And Detection Standard, Advanced Electrical Installation Work- Trevor Linsely

About Syed Noman ud din

Syed Noman ud din is an Electrical Engineer and working in Industry from last 3 years. He writes technical articles for electrical and electronic engineers. He has also published several research publications in renowned international journals.

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