UMH MINE FIRES By PK Maheswary SS college
UMH MINE FIRES By PK Maheswary SS college of Engineering
Three basic ingredients are necessary for occurrence of fire: • Fuel • Oxygen and • Heat source
Fire Triangle • A basic knowledge of a fire triangle is essential to the understanding and control of fires.
• Without sufficient heat, a fire cannot begin and cannot continue. • Heat can be removed by • dousing with water • Introducing particles of powder or any gas in the flame • Turning off the electricity in an electrical fire removes the ignition source. • Without fuel, a fire will stop. • Without sufficient Oxygen, a fire cannot begin and cannot continue. – With a decreased oxygen concentration, the combustion velocity lowers down.
GENERAL CLASSIFICATION OF FIRES • There are four classes of fires depending upon the kind of material involved. • Each class designates the fuel involved in the fire, and thus classifications allow selection of most appropriate extinguishing agent. • For example, non-conductive extinguishing agents are used for electrical fires. • Class A fires are the "Ordinary combustible" fires involve solid, organic material such as – Paper – Wood – Cloth – Rubber and – Plastics • These materials leave ashes or residue.
• This class of fire is fairly simple to fight and contain - by simply removing the heat, oxygen, or fuel, or by suppressing the underlying chemical reaction. • The most common way to do this is by removing heat by spraying the burning material with water. • Oxygen can be removed by smothering the fire with foam from a fire extinguisher.
• Class B fires involve flammable liquids, gases and greases such as – Petrol – Oils – Paints and – Solvents • Most effective way to extinguish a liquid or gas fueled fire is by inhibiting the chemical chain reaction of the fire, which is done by dry chemical and halon extinguishing agents. • A CO 2 fire extinguisher used for flammable liquids and gasses. • For liquids, foam is also sometimes effective.
• Class C fires-Electrical fires involving live electrical equipment, viz. – Motors – Switches and – Other electrical appliances • Caused by, for example, short-circuiting machinery or overloaded electrical cables. • These fires can be a severe hazard to firefighters using water or other conductive agents: Electricity may be conducted from the fire, through water, the firefighter's body, and then earth. • Electrical shocks have caused many firefighter deaths. • Electrical fire may be fought in the same way as an ordinary combustible fire, but water, foam, and other conductive agents are not to be used. • CO 2 and dry chemical powder extinguishers are especially suited to extinguish this sort of fire. • Once electricity is shut off to the equipment involved, it will generally become an ordinary combustible fire.
• Class D fires involve combustible metals such as – Magnesium – Titanium and – Sodium • Magnesium and titanium fires are common. • When one of these combustible metals ignites, it can easily and rapidly spread to surrounding ordinary combustible materials. • Water and other common firefighting materials can excite metal fires and make them worse. • It is recommended that metal fires be fought with 'dry powder' extinguishing agents, viz. chloride granules and graphite powder. • Dry Powder agents work by smothering and heat absorption.
Classification of Mine Fires in mines may be divided into two types: 1. Open fires and 2. Incipient or concealed fires 1. Open fires: • Caused as a result of ignition of a combustible material. • Characterized by visible active combustion or flame. • These fires usually originate in open mine workings, viz. – shafts, – roadways, – coal faces and – other openings that form part of the ventilation system of the mines.
• They spread quickly in direction of ventilation, the rate being depending upon – the kind and quantity of the combustible material, – the amount of air reaching it, and – velocity of the air current. • In any case they develop much faster than the incipient fires.
2. Incipient or concealed fires: • These fires are also called seam fires. • They usually occur in the areas that are difficult or impossible to access, viz. – caved or abandoned zones, – discontinued mine workings, – goaves, – fall of roof coal, – fractured coal pillars and – vicinity of geological disturbances. • These are usually, but not necessarily initiated as a result of spontaneous combustion and can occur in both coal and sulphide ore minerals. • They account for 75 -90% of all underground mine fires, and are difficult to detect in their early stages. • The degree of fire propagation and polluting the mine atmosphere depends upon the rate at which air leaks through the areas affected.
On the basis of the origin/mode of ignition fires in mines may be classified as • Exogenous fires: – Initiated due to piloted ignition i. e. ignition from an external source of energy. – Most incidences of fires in mines of US and UK are exogenous origin. • Endogenous fires: – Due to spontaneous heating phenomenon of the fuel/material concerned (coal/pyrites). – More common in Indian mining scenario.
Causes of mine fires For mine fire to break out, the following three conditions must be fulfilled. 1. Combustible material must be available in sufficient quantity 2. Sufficient supply of O 2 must be available 3. A source of ignition of adequate energy must be present.
The various causes of mine fires may be grouped under the following headings: 1. Open flames • Use of naked or open lights in mines • Careless handling of lamps • Carrying matches or other flame making devices 2. Spontaneous heating • Due to self heating of coal or easily oxidizable substance due to auto oxidation 3. Electricity: • Due to short-circuiting and sparking due to improper methods of installation may ignite any combustible material present in the immediate vicinity
4. Friction • Fires due to frictional causes occur in roadways and inclines in which rope haulage and belt conveyors are installed • In coal faces which are cut by coal cutting machines, continuous miners or shearer loaders. • Belt conveyor fires form the largest percentage of these fires. Causes of belt conveyor fires: • Overheating at the drive pulley due to their continuous rotation against the stalled or slipping belt. • Overheating at the carrying and return idlers rotating against obstruction and • Overheating of brakes and gears
5. Blasting (minor cause) • Blown-out shots in coal especially when coal dust is present in shot-holes may cause mine fires through ejected glowing particles • Blasting can also ignite unknown methane blower which in turn may set an entire coal face on fire
6. Explosions: • Fire damp and coal dust explosions may lead to smoldering and active fires • Explosion flames, explosion gases and coal dust taking part in an explosion may set on fire – – – wooden doors, paper, non-fireproof brattice line, pieces of clothing, unburnt coal dust and loose coal, and ultimately coal faces.
7. Miscellaneous: • Welding, cutting and soldering operations with open flame u/g may result in mine fires • Methane blowers may catch fire • Static or frictional electricity may cause fire indirectly from flammable fire damp-air or coal dust-air mixtures • Friction of belt against pulleys and passing of dust laden air trough ducting • Diesel powered equipments
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