ELECTRICALLY- CAUSED FIRE

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1 Introduction to ELECTRICALLY- CAUSED FIRE Richard Nute Product Safety Consultant San Diego Rev A.01, 0

2 agenda DEFINITION ELECTRICALLY-CAUSED FIRE VIDEO DEMONSTRATIONS FIRE SAFETY and TV SETS, FIRE CONCEPTS and BEHAVIOR GE COFFEEMAKER FIRE PYROLYSIS, IGNITION, FLAMING, FIRE, and COMBUSTION ELECTRICAL ENERGY CONVERSION TO THERMAL ENERGY Rev A.01, 1

3 Electrically-caused fire Electrically-caused fire is electrical heating of a material to ignition temperature followed by ignition and combustion. Rev A.01, 2

4 Fire Video Demonstration European Flame Retardants Association Fire Safety and TV Sets 17 minutes Rev A.01, 3

5 Fire Video Demonstration NFPA Fire Concepts and Behavior circa 1970 > Note the physical state of the fuel necessary for flame. < 18 minutes Rev A.01, 4

6 Fire Video Demonstration ABC News GE Coffeemaker Fire Excerpted from Prime Time, October 17,1991 > Note the description of the physical state of the flaming fuel. < 3 minutes Rev A.01, 5

Gases Pyrolysis products include non-combustible gases combustible gases liquids solids,

7 Pyrolysis Pyrolysis is the transformation (usually chemical decomposition) of a compound into one or more other substances by heat alone. Gases Pyrolysis products include non-combustible gases combustible gases liquids solids, including soot Liquids Fuel Solids Jurgen Troitzsch, International Plastics Flammability Handbook, Hanser Publishers, Rev A.01, 6

8 Conservation of energy Radiated power output Convected power output Fuel Conducted power output Electrical power input Rev A.01, 7

9 Ignition process Flames Oxygen Gases Igniter or more heat Fuel Rev A.01, 8

10 Ignition and ignition types Ignition is the process of initiating self-sustained combustion of gases. Oxygen Flames Flash/pilot ignition is ignition of the gases evolved from the fuel by a spark or flame. Gases Igniter or more heat Auto-ignition/self-ignition is ignition in the absence of a spark or flame. Spontaneous ignition is ignition by an internal chemical or biological reaction producing sufficient thermal energy to raise the material temperature to auto-ignition temperature. Fuel Fire and explosion investigations, NFPA 921, National Fire Protection Association, Rev A.01, 9

11 Flaming combustion processes Heat Gases Flames Heat Oxygen Oxygen Fuel Rev A.01, 10

Diffusion flame has the oxygen diffused into the gas mixture from the surrounding atmosphere, e.g., a candle flame, a cigarettelighter.

12 Flame and flame types Flame is the luminous portion of burning gases. Pre-mixed flame has the oxygen-gas composition fixed prior to combustion, e.g., a Bunsen burner flame, a gas stove. Diffusion flame has the oxygen diffused into the gas mixture from the surrounding atmosphere, e.g., a candle flame, a cigarettelighter. Jurgen Troitzsch, International Plastics Flammability Handbook, Hanser Publishers, Rev A.01, 11

13 Flame behavior Flames are burning gases. The path of the burning gas is the same as the path of a hot gas. The flame is always vertically-oriented unless deflected by an object or by air currents. The volume of the flame is nearly constant. Rev A.01, 12

14 Fire and fire types Fire is a rapid oxidation process evolving thermal, chemical, and light energy in the form of flames. Fuel-regulated fire is a fire where the heat release rate and fire growth rate are controlled by the fuel characteristics. The supply of oxygen is relatively unlimited. Oxygen-regulated fire is a fire where the heat release rate and fire growth rate are controlled by the supply of oxygen. The supply of fuel is relatively unlimited. Jurgen Troitzsch, International Plastics Flammability Handbook, Hanser Publishers, Rev A.01, 13

15 Combustion Combustion is a self-sustained hightemperature oxidation reaction. Flaming is a gas-phase combustion process. Glowing is a solid-phase combustion process. Smoldering is an oxygen-regulated solid-phase combustion process. Jurgen Troitzsch, International Plastics Flammability Handbook, Hanser Publishers, Vytenis Babrauskas, Ignition Handbook, Fire Science Publishers, Rev A.01, 14

16 Glowing combustion process Gases Fuel Liquids Solids Heat Glowing Oxygen Rev A.01, 15

17 Electrical heating Electrical heating occurs when ELECTRICAL ENERGY is converted to THERMAL ENERGY. Electrical energy is converted to thermal energy in a RESISTANCE. Electrical heating is expressed in WATTS. 1 watt = 1 joule/second P = I 2 * R P = E 2 / R P = E * I Rev A.01, 16

18 Conversion to thermal energy Power distribution devices I I Zsource Rdist Zsource Rdist Esource Z load Esource Z load Rdist Rdist Effects of load faults P = I 2 * R Effects of distribution faults P = I 2 * R Rev A.01, 17

19 Conversion to thermal energy Power consuming devices I I Zsource Zsource Esource Z load Esource Z load Effect of component faults. P = E * I Effects of source faults. P = E 2 / R Rev A.01, 18

20 Heating All heating (temperature rise of an object) is an exponential rise as a function of time. Start temperature is object s initial temperature. End temperature is heat source s temperature minus coupling and environmental losses. Rev A.01, 19

21 400 Thermal Time Constant 350 Temperature, degrees C Time, minutes Rev A.01, 20

22 Thermal Time Constant Effect of TC on curve shape Thermal t ime const ant TC = 10 TC = 7.5 TC = 5 TC = 2.5 TC = 1 30 T t = T f (1- e -t/ TC ) 20 T t is t emperat ure at any t ime T f is f inal t emperat ure 10 t is time TC is t he t hermal t ime const ant Time, minut es Rev A.01, 21

23 FIRE CONCEN- TRATION GASES AND IGNITER OXYGEN PYROLYTIC GASES AND THERMAL ENERGY FUEL MATERIAL AND ELECTRIC ENERGY RESISTANCE Rev A.01, 22

24 Heat Rev A.01, 23 Solids Gases Fuel Glowing Heat Igniter or more heat Oxygen Flames Heat Oxygen Liquids

25 Introduction to ELECTRICALLY- CAUSED FIRE end Rev A.01, 24

Introduction to Fire Protection Systems

PDHonline Course M110 (4 PDH) Introduction to Fire Protection Systems Instructor: Lawrence J. Marchetti, P.E. 2012 PDH Online PDH Center 5272 Meadow Estates Drive Fairfax, VA 22030-6658 Phone & Fax: 703-988-0088