Unit 2g Fire Hazards PDF

Fire Hazards ______________________________________________ Lecture Objectives i. Define Fire, and describe Fire triangle and tetrahedron; fire as chemical reaction ii. Describe the American and European fire classification and identify the classification used for Trinidad and Tobago ii...

Fire Hazards ______________________________________________ Lecture Objectives i. Define Fire, and describe Fire triangle and tetrahedron; fire as chemical reaction ii. Describe the American and European fire classification and identify the classification used for Trinidad and Tobago iii. Explain the basic principles of fire prevention using the fire triangle and describe the prevention of fire spread in buildings iv. Identify the different types of extinguishers for first aid response and list the corresponding class of fires they could extinguish v. Outline the relevant regulatory requirements under OSH Act _______________________________________________________________________ The personal and economic costs of fires are enormous. It is important to know how to prevent or reduce the potential for fires and also to be able to effectively deal with a fire situation should one occur. How Fires Start An understanding of the chemical reaction of a fire forms the basis for the knowledge necessary to extinguish a fire. Ordinary fires result from the combination of fuel (any material that is burned or altered to obtain energy and to heat or to move object), oxygen and heat. When a combustible substance is heated to its ignition temperature, it will burn as long as there is a supply of oxygen. Thus fuel, oxygen and heat are the three ingredients necessary for a fire to start.  Fire hazards eg  Overloaded electrical system, broken electrical wires, sockets  Fuel store areas with high oxygen content or sparks  Objects that block fire exits, extinguishers, escapes, muster points  Faulty or empty extinguishers, fire alarms  Inadequate emergency response ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 1   Overloading of equipment eg pumps for flammable gases  Overcrowding  Smoking in non-designated areas  Oily rags can spontaneously combust  Volatile liquids etc. that give off flammable vapours  Static electricity  Controls eg  Fire proofing areas, isolating areas  Fire walls  Proper storage and housekeeping  Proper maintenance of equipment  Correct selection, placing, training, use, and inspections on fire safety equipment  Proper ventilation to diffuse flammable gases  Proper emergency response including drills  Administrative controls eg proper procedures, provision of MSDS  Training of personnel in fire fighting Ignition Sources Heat is the most common source of ignition. Consequently anything that can supply heat to a fuels source is a potential ignition source. We will now briefly look at some common ignition sources: Friction – there are two elements to consider here; friction in machinery and those metals which tend to give a thermite reaction (A pyrotechnic composition of a metal powder and a metal oxide which produces a short burst of extremely high temperatures focused on a very small area for a short period of time.) Friction in machinery arises from friction in beatings or from metal surfaces in direct or contact and moving relative to each other. The spread of the fire can then be further accelerated by the oil and grease on nearby surfaces. The way to control this situation is prevention via proper maintenance, including appropriate lubrication and proper machine setting. The second aspect concerns certain metals which have an affinity for oxygen and in a thermite reaction with rust can produce temperatures of 3000 C. For example, if a tool of aluminum alloy is dropped onto rusty steel a thermite flash can result. Hot surfaces can occur in many processes and hazards can be reduced by appropriate insulation. For example, consider at the end of the day staff using tools for welding, cutting ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 2  and drilling. If they are packed away, before they have cooled down, in a storage area with gas cylinder, solvents and other flammable materials. A recipe for disaster! Proper checks should be made at the end of the day to ensure that no such potential fire situations exist. Electricity and electrical equipment – electricity itself is not a source of ignition. It is the arcing that results from making or breaking a circuit, or the heat that arises from the passage of current through a wire that is the source. These issues are of particular importance where electrical equipment is used in flammable or explosive atmospheres. Under such conditions, the equipment must not produce a spark and be protected in some way to prevent any arcing. Under normal conditions, arcing, sparking or overheating can be eliminated by using proper maintenance programmes. Static electricity – occurs when there is relative motion between and/or separation of two dissimilar materials. The charge can be transported some distance before it becomes great enough to cause a discharge which is the source of ignition. Some examples of static charge generation include conveying of powders, belts and pulleys, flow of liquids in pipelines and setting of particles in liquid e.g. rust. The solution to this problem, lies with prevention this is usually achieved by providing an earth to facilitate safe discharge. Where there are flammable materials precautions such as anti-static clothing and footwear are advisable as well as anti-static flooring. Electrostatic charges build up when liquid is pumped through pipelines, the charge depending on the electrical conductivity of the liquid. If this is high then the charge is easily generated but quickly dissipated. The charge rate increases with increased fluid flow and where there are constrictions in the pipe such as filters and valves or bends. Earthing is normally effective, except for liquids with low electrical conductivity; in such cases the use of an anti-static additive may be desirable as this would increase the electrical conductivity to a safe value. Open flames – cigarette smoking is one of the principal causes of fire particularly arising from careless disposal of the match or stub end of the cigarette. The obvious approach is to ban smoking in the work are or anywhere around flammable material. We have looked at potential ignition sources and how these can be controlled. Another way to minimize the likelihood of fire is to control the fuel source. Much of it comes down to the basic concept of GOOD HOUSEKEEPING. Waste and spillage – discarded waste material such as oily rags, paper and packaging should be cleared away and stored in non-flammable containers. Flammable liquids – the safe use, storage and transport of these substances will minimize any fire risk. These issues will be discussed in module 9. ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 3  Gases – The fire risk occurs when there is a release of the gas from the container or pipeline. This can be controlled or prevented by careful system design, implementation of safe systems of work and good maintenance programmes. Dusts – a dust cloud can have many of the fire characteristics of a gas. Control measures would involve preventing dust accumulation, damp sweeping or vacuuming and the use of appropriately designed electrical equipment i.e. flameproof. Classification of Fires Symbol/Pictogram Classification of fire Appropriate Extinguisher CLASS A Water, Foam, ABC Dry Powder and Wet All solid materials, usually organic nature Chemical (contains compounds of carbon) and generally Extinguishers. produce glowing embers – i.e. wood, textiles, Extinguishers with curtains, furniture and plastics. white, yellow or blue labels. CLASS B Foam, ABC Dry Powder, Monnex Dry All flammable liquids and solids, which can Powder and CO² Gas also be sub-divided into: Extinguishers.  Non- miscible with water i.e. petrol, oils, Extinguishers with solvents, paints & waxes yellow, blue (not L2 or  Polar liquid Fires with water e.g. alcohol, M28 Powder) or black methanol, acetone, propanol & ethanol. labels. CLASS C ABC Powder and Monnex Dry Powder Class ‘C’ fires involve Natural mains gas, liquid Extinguishers. Petroleum Gases (e.g. LPG – Butane & Propane Extinguishers with etc) and medical or industrial gases. blue labels (not L2 or M28 Powder). CLASS D L2 Powder and M28 Powder Extinguishers Class ‘D’ fires involving metals or powdered (M28 Powder does not metals etc (where water is generally ineffective cover lithium). and/or dangerous). Extinguishers with Specialist Dry powders are produced for certain blue labels (not ABC Class “D” fires particularly those a\involving or Monnex Dry alkali metals such as sodium & potassium to Powders). form a crust, which excludes oxygen from the ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 4  surface of the molten metal. A specific agent is added to prevent the powder from sinking into the surface of the molten metals. ABC Powder, Electrical fires are not considered to constitute a Monnex Dry fire class on their own, as electricity is a source Powder and of ignition that will feed the fire until removed. CO² Gas When the electrical supply has been isolated, Extinguishers. the fire can be treated (generally) as ‘Class A’ Extinguishers for extinguishing purposes. However, you with blue (not should always isolate the supply before fighting L2 or M28 the fire; if this is not possible then a non- Powder) or electrical conducting extinguishing agent is to black labels. be used regardless of the power status, on all occasions. Warning Note! – Some electrical equipment can store in capacitors, lethal voltages even if their power supply has been isolated. Always use extinguishers containing a non-electrical conducting extinguishing agent specifically designed for use on electrical equipment such as carbon dioxide or Dry Powder. Wet Chemical Class F : Extinguishers. New class specifically dealing with high Extinguishers with temperatures (≥ 360C) cooking oils used in yellow labels large industrial catering kitchens, restaurants and takeaway establishments` etc. Cooking oil fires, because of their high auto-ignition temperatures, are difficult to extinguish. Conventional extinguishers are not effective for cooking oil fires, as they do not cool sufficiently or may even cause flash back, thereby putting the operator at risk. These extinguishers contain a specially formulated wet chemical which, when applied to the burning liquid, cools and emulsifies the oil, extinguishing the flame, sealing the surface and preventing re-ignition. ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 5 Fire Extinction Once a fire has started the objective is to extinguish it, preferably as quickly as possible to minimize damage and to prevent injury. In other words you are removing one or more sides of the fire triangle. Starvation – Removal of unburnt material or removal of burning material. If the fuel is being supplied from a pipe or tank, closing the supply valve will clearly stop the supply. Smothering – Essentially this method is restricting the oxygen supply. This can be done by introducing an inert gas or covering the burning area with foam or sand. Cooling – this is the most common means of extinguishing a fire, water being the cheapest and most effective medium. Ultimately insufficient heat is supplied to the fuel and continuous ignition ceases. Direct interference with the oxidation reaction - can be achieved by using fluorocarbons. Portable fire extinguishers – contain an extinguishing medium which can be expelled by the action of internal pressure and directed at the fire. It's easy to remember how to use a fire extinguisher- simply follow the steps- "P-A-S-S" Pull the Pin: Pull the pin at the top of the extinguisher that keeps the handle from being pressed. Break the plastic seal as the pin is pulled. Aim: Aim the nozzle or outlet toward the fire. Some hose assemblies are clipped to the extinguisher body. Release the hose and point. Squeeze: Squeeze the handle to release the extinguishing agent. The handle can be released to stop the discharge at any time. Before approaching the fire, try a very short test burst to ensure proper operation. Sweep: Sweep from side to side at the base of the fire until it is out. After the fire is out, watch for remaining smoldering hot spots or possible reflash of flammable liquids. Make sure the fire is out. Care of Portable Fire Extinguishers Fire extinguishers require regular, periodic inspection and maintenance to ensure efficient and safe operation. Portable fire extinguishers should be given a quick check every three months to give reasonable assurance that: ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 6  1. They have not been activated. Wire seals should be intact. 2. Hose and horn are free obstructions. 3. There is no physical damage or deterioration. Record the inspection date on the tag and initial it. Extinguishers must be kept fully charged at all times and must be recharged immediately after use even though only partially discharged. Fire Protection Fire precautions can be divided into fire prevention and fire protection. We have already looked at many ways of preventing fires. This section now looks at ways of fire protection. There are two elements to fire protection, namely:  Structural precautions  Early fire detection.  Structural Precautions: in the event of a fire in a building, the more the spread of the fire can be controlled and the longer the building remains intact i.e. before collapsing, then the greater the chance that people will escape without injury. Certain requirements may be specified in legislation.  Sprinklers (free of corrosion, adequate water supply, proper design/elevation, free of debris/clogging,  Hydrants and hoses ( stored in dry heated areas, leak and pressure tested, folded and unfolded regularly)  Alarms (manual or automatic) Early Fire Detection: There are two ways that the early presence of fire can be detected and these are via fire detectors and/or fire alarms. Fire detectors work on one of these three principles: Thermal Detector - activated by heat sound only when the temperature rises to a certain level. They are not as safe as the ionization and photoelectric types in that the fire must be more intense it will sound. Can be used in areas where smoke triggers false alarm eg near stoves. Ionization Detector - responds to smoke and gas particles from a flaming fire. Invisible particles are ionized in the heat of combustion. A current passes through this "ionized" air. When smoke particles enter the detector, they impede the flow of current. An alarm is programmed to sound when the current gets too low. Photoelectric Detector - responds to smoke from a smoldering fire. They use a small lamp adjusted to direct a narrow light beam across the detection chamber. Next to this light source is a light-sensitive photocell. Smoke entering the detection chamber scatters the light beam reflecting it in all directions. Some of this reflected light is picked up by the photocell which, at a preset level, triggers the alarm. ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 7   OSH Act makes fire provisions under Part V  Certification by fire authority & Recertification when establishment changes  Maximum number of persons  Drills  Emergency exits and escapes clearly marked, free of obstruction, unlocked or easily opened, well-lit or use of emergency lighting where necessary  Audible warning alarms  Fire equipment provided, maintained readily available Exercise 8.1 1. Name and describe the major categories of fires, stating the types of extinguishers used in each case. 2. Why are electrical fires not categorized? 3. What type of extinguishers can be used on electrical fires and what types cannot? 4. What type of extinguisher is used to put out electrical fires? 5. Why is it sometimes necessary to spray a sealed container, such as a drum or tank truck, with water if there is fire nearby? 6. What makes electricity capable of causing fires? 7. Identify conditions for which a Portable Fire Extinguisher should NOT be used. 8. Discuss, fire exit signs should be made with a white background and red letters. 9. Discuss, water can be used to extinguish fires started by paper. 10. Discuss, class F is the most recent Class of Fire to be added to the list and covers fires started from high temperature cooking oils or fats. 11. How many persons must be employed in an industrial establishment for the requirement of a Company Fire Plan? 12. What is the recommended method for using a fire extinguisher? ________________________________________________________________________ HSEV 1005 – Introduction to health, safety and environment Unit 2g - Fire Hazards Amna S Imamshah 8