Basic Fire Science : Test 1 – 9 February 2019 What is Fire? - Fire is a chemical reaction, a rapid oxidation reaction called combustion that combined fuel and oxygen with an applied ignition source. Thus resulting the release of products such as smoke, heat and light at a different intensity. Ignition sources? - Electrical equipment, hot surfaces, static electricity and naked flames. Controlling of elements: 1. Most difficult: Oxygen 2. Almost likely can be controlled : Ignition sources 3. Definitely easily to be controlled: fuel, housekeeping and storage management Principle of Fire Prevention: 1. Control of Fuel - Achieve through good housekeeping and storage management such as local exhaust ventilation, purging and degassing, permit to work system. 2. Control of Ignition sources - Achieve through bonding and grounding, area and equipment classification and permit to work system. 3. Control Oxygen Achieve through inerting, blanketing and use of flammability diagram to limit oxygen concentration. Stages of combustion: 1. 2. 3. 4. Induction/ Initiation stage Growth/ Propagation stage Fully developed Decay Induction/Initiation stage 1. Interaction of correctly proportion fuel, oxygen and heat source 2. Combustion reaction starts Growth/Propagation stage 1. Sustained or self-sustained 2. Zone A : Flashover zone 3. A flashover is a temperature dependent fire phenomenon that will accelerate the rate of reaction rapidly and increase the temperature of the fire at the short span of time, involving burning the items at the same time, moving the combustion process to the next stage. Fully developed stage 1. Steady rate of fire 2. Characterized by massive flames and high temperature of 500C. Decay stage 1. Rate of reaction decreases 2. As the amount of fuel depleted the rate of reaction slows down and eventually extinguished itself. 3. Temperature decreases 4. Fuels depleted 5. Fire reaction stops Heat transfer methods: 1. Conduction, convection and radiation - Conduction is a method of heat transferred that involves direct contact of surface materials. Most commonly solid made materials within the building. Not the most prevalent method of fire spread, as the materials are limited to the thermal conductivity. - Convection is a method of heat transferred that involves indirect contract of surface material. Fire spread involves the movement of gas-layer of liquid layer from hot area to cooler area. - Radiation is a method of heat transferred that involved no contact of material. Fire spread involves solid or liquid material being exposed to thermal infrared electromagnetic radiation. Absorbed infrared radiation raises the temperature of solid and liquid exposed. Combination of all 3 = Direct burning/Flame impingement Factors influencing the spread: - Fuel load, occupant load, ventilation and element of structure Fire Classification National Fire Protection Association (NFPA) Classification of Fire (SS 578: 2012) – 5 Categories 1. Class A : fire involving ordinary combustible solids such as clothing, paper and wood 2. Class B: fire involving flammable or combustible liquids such as gasoline, kerosene and diesel 3. Class C: fire involving flammable or combustible gases such as Methane, Propane Liquified Petroleum gas 4. Class D: fire involving combustible metals such as sodium, lithium, magnesium and aluminium 5. Class F: fire involving cooking media/oil in commercial kitchens such as vegetable oil Basic Fire Science – Explosion Explosion is a superfast and violent oxidation reaction, that gives off heat, smoke, light and overpressure with great intensity. Types of explosion: 1. Physical and chemical explosion 2. Physical explosion : overfilled balloon burst 3. Chemical explosion: a violent oxidation reaction Chemical explosion - Combustion wave front : flame front Pressure wave front : Blast front How to prevent explosion? 1St Principle: Fuel control - Eliminating an explosive atmosphere Prevention method: local exhaust ventilation (lev), use of inert gases, removal of dust 2nd Principle: Ignition control - Eliminating an ignition sources Hazardous area classification Use of intrinsically safe equipment 3rd Principle : Diverting explosion effects - Protection methods : explosion venting, rapid explosion suppression system
