Plant Fire Safety - 4th Class Edition 3 - PDF

Unit A-4 • Introductionto Plant and Fire Safety OBJECTIVE == 1 Discuss the theory, terminology, and the life safety issues associated with fires. ( FIRE THEORY Combustion is defined as an exothermic reaction (gives off heat). This self-sustaining reaction involves a solid, liquid, and/or gaseo...

Unit A-4 • Introductionto Plant and Fire Safety OBJECTIVE == 1 Discuss the theory, terminology, and the life safety issues associated with fires. ( FIRE THEORY Combustion is defined as an exothermic reaction (gives off heat). This self-sustaining reaction involves a solid, liquid, and/or gaseous fuel. The reaction is usually associated with the oxidation (combining with oxygen) of a fuel, generation of heat, and the emission of light. There are many types of fuel and many sources of oxygen besides what is found in the air. Some fuels contain enough oxygen in the fuel material itself that combustion is possible even in an inert atmosphere. For combustion to occur, the following four criteria must be met. 1. There has to be a fuel to burn. 2. There has to be oxygen to "oxidize" it. 3. There has to be an ignition source. 4. The fire must be able to continue burning. When a wood log is completely burned, only ashes are left. The combustible parts of wood will burn with the oxygen in the air and generate heat. Fuel is technically identified as a reducing agent. The air that supplies the oxygen for burning is an oxidizing agent. There are many different types of reducing agents that will burn in the presence of an oxidizing agent, so that when intense heat is added, then a fire starts. While burning, the temperature stays ( high enough to increase the molecular activity of the reducing agent - which enables the fire to continue. Reducing Agent = Fuel Oxidizing Agent = Anything that supplies oxygen Intense Heat = A spark, a match, or anything else hot enough to raise the temperature and ignite the fuel Therefore, to be a self-sustaining, uninhibited chain reaction, the fuel must: a) Continue to burn b) Generate heat c) Maintain a high enough temperature to sustain ignition Experience shows that wet wood is very difficult to burn. The water in the wood converts to steam and draws heat away from the fire. The remaining heat may be insufficient to keep the temperature of the combustion reaction above its ignition temperature. The wetter the wood, the lower the temperature. Wood that is too wet will not generate enough heat to sustain the chain reaction, and the fire will go out. ( 4-4 <(-------------------------------4t_ h _C-I_ as_s_E_d_ft_w_n_3• P _a_r_l_ A Plant Fire Safety • Chapter 4 ============================== == Oxidizing Agent Oxidizing agent refers to any chemical element or compound that can provide oxygen and combine with a fuel in the combustion process. Oxygen is the simplest and most common oxidizing agent. However, many other chemicals that are found in power plants can also be oxidizing agents. The following are examples: a) Oxygen and ozone- ozone is highly reactive with fuel - and has extra oxygen readily available for combustion b) Hydrogen peroxide c) Members of the halogen group such as fluorine, chlorine, bromine, and iodine d) Concentrated nitric and sulfuric acids e) Oxides of heavy metals such as manganese dioxide and lead oxide f) Nitrates, chlorates, percholates, and peroxides g) Chromates, dichromates, permanganates, hypochlorites, and hypobromites Most accidental fires involve a reaction primarily with air. Atmospheric air is about 21% oxygen by volume. The balance is mainly nitrogen, which plays no part in the combustion process. Reducing Agent As mentioned above, a reducing agent is any combustible material. This fuel combines with oxygen provided by an oxidizing agent and burns. The following are the most common materials involved as fuels (reducing agents) in fires. a) Nonmetals such as carbon, sulfur, and phosphorous. b) Hydrogen. ( c) Carbon monoxide. Carbon monoxide can result from incomplete combustion. It will combine with oxygen to generate heat as it forms carbon dioxide. d) Compounds rich in carbon and hydrogen. Materials high in both carbon and hydrogen content include common fuels, and are highly flammable. Examples of hydrocarbons that burn readily are: • Methane • Ethane • Propane • • • • • Butane Natural gas Acetylene Gasoline Fuel oils • Wood • Coal • Cellulose e) Metals such as aluminum, magnesium, titanium, zirconium. f) Alkali metals such as sodium and potassium. ( 4th Class Edition 3 • Part A 4-5 Unit A-4 • Introduction to Plant and Fire Safety A fire requires four components to burn, and is represented by the fire tetrahedron illustrated in Figure 1: ( Figure 1 - Fire Tetrahedron Temperature Fuel (Reducing Agent) Oxygen (Oxidizing Agent) Uninhibited Chain Reaction All four components of the fire tetrahedron are required for there to be a fire. 1. Fuel 2. Oxygen ( 3. Ignition (heat) 4. Uninhibited (self-sustaining) chain reaction Therefore, in order to extinguish or prevent a fire, remove any one of four components. a) Remove the fuel so there is nothing to burn. b) Remove the oxygen by smothering the fire (such as with an inert gas). c) Keep the fuel or air below the ignition temperature. No matter how combustible a material is, and how much oxygen is present, it must be hot enough to ignite or there will be no fire. d) Stop the chemical chain reaction. A Power Engineer may notice a buildup of soot on an oil-fired burner in a boiler where there is insufficient combustion air or turbulence. This incomplete combustion will result in unburned particles of soot coating the boiler furnace surfaces. Rapid combustion is when a fire quickly releases large amounts of heat and light energy, which results in a rapidly expanding flame. This form of fire occurs in internal combustion engines. Detonation is the term used to describe the rapid ignition that occurs in an internal combustion engine. Many solid fuels, such as coal and wood, contain both volatile combustible material (VCM) and carbon. The VCMs are organic hydrocarbons that become gaseous when the fuel is heated. These vapours ignite and burn with a visible flame. The carbon in the solid fuel burns without a flame. Liquid fuels do not burn directly. They must first be heated to a high enough temperature to produce sufficient flammable vapour to support combustion. Then, the vapours ignite, producing visible flames. Some liquids, such as methanol, produce faint flames that may not be visible, depending on the lighting conditions. 4-6 €--/ S _ 4th Class Edition 3 • Part A ( Plant Fire Safety • Chapter 4 ( Gaseous fuels do not require preheating to produce combustible vapours. They only require sufficient mixing with air or oxygen and an ignition source. Gaseous fuels burn with visible flames. Hydrogen gas burns with such a faint visible flame that it may not be noticeable, depending on the lighting conditions. The first stage of a solid fuel fire is the preheating phase, where the fuel is heated up hot enough to burn. The next stage is the distillation phase or gaseous phase, where the mixture of air and flammable gases have been ignited. In the gaseous phase, flames are visible and the fire is selfsustaining. The third stage, known as the charcoal phase or solid phase, is when a solid fuel such as wood or coal is reduced to embers. In this stage, combustion of the remaining glowing carbon takes place with nearly invisible flames. This form of combustion may be called flameless or glowing combustion. The embers burn, giving off light and heat, but the self-sustaining reaction is much slower. Fires can burn in this slow, self-sustaining way for prolonged periods of time, such as in subsurface peat bogs or coal mine fires, and can be very difficult to extinguish. FIRE SAFETY The threat to life from a fire comes from: • High temperatures • The gaseous products of combustion • The depletion of oxygen in the vicinity of the fire The gaseous products of combustion are toxic and can have immediate and long-term health effects, including death. Also, these gaseous combustion products displace air, which leads to oxygen deficiency. Note: a) At oxygen concentrations of about 17%, a person will suffer impaired thinking and reduced muscular coordination. b) In the range of 10 to 14%, the individual may still be conscious, but will show abnormal fatigue on exertion and impaired judgement. c) Below a concentration of 10%, an individual will lose consciousness and will quickly need fresh air or oxygen to be revived. The levels of impairment will be greater if the person requires increased oxygen due to exertion. In a fire, smoke fills the environment, causing it to be difficult to see and breath. The toxicity of the smoke causes irritations to the eyes and lungs. Disorientation can result. People can get lost even in a familiar layout. Therefore, when in a fire, stay as close to the floor as possible where heavier oxygenated air is concentrated. If possible, breathe through a wet filter, such as clothing or a towel. Additional precautions must be taken when entering an enclosed fire area. The oxygen in the room may become depleted and the fire may be diminished. However, the fire can resume rapidly if air (oxygen) is reintroduced when a door or a window is opened. This allows more air to flow into the room. When the fresh oxygen feeds the hot combustible gases, it can result in an explosion. Early detection is a major way to effectively control a fire condition. Power Engineers working in commercial buildings, hospitals, or schools are often trained as first responders to a fire situation. They will recognize the importance of a quick response in order to catch a situation early before it can develop into something bigger. Minutes, even seconds can count. Responding to a situation in the very early stages can be the difference between fighting a small paper fire or a large, tougher to extinguish fire. Fire and other emergency situations can cause major physical and psychological stress. People will often behave erratically, which will have negative impacts in emergency situations. Panic, confusion, and disorientation can rapidly set in. 4th Class Edition 3 • Part A 4-7 Unit A-4 • Introduction to Plant and Fire Safety For example, people may head in the wrong direction or simply freeze-up, unable to perform routine tasks in familiar surroundings. Mistakes can be made, if the person attempting to respond to the fire is panicking. It is often difficult to determine why one person will be calm and another person will be in a state of panic. When people panic, it can significantly interfere with the ability of others to respond to a fire or other emergencies. ( An effective training method for people to deal with emergency situations is to have repeated exposure by practicing. Simulated emergencies teach people how to respond calmly in real situations. Most companies will have regula r "fire drills': where an alarm is sounded and the building is evacuated. This gives everyone in the company an opportunity to calmly "walk through" what would need to happen in the case of a real emergency. Fire Drills One of the most effective ways to prepare for a fire emergency is by having regular fire drills. Steps are established and practiced repeatedly until everyone is familiar with the procedures. Fire drills are often initiated by sounding a fire alarm. This notifies the occupants that they need to exit the building calmly, quicldy, and in an orderly manner. For fires local to a small area, some staff may be trained as first responders to take action. For example, a method called "REACT" can be used for this purpose. REACT is an acronym outlining a set of steps that can be initiated as follows: • Remove people from immediate danger • Ensure the doors are closed • Activate the alarm • Call the fire department • Try to extinguish the fire, BUT ONLY IF IT IS SAFE TO DO SO! The above steps are intended to be followed in order. Note that the last step is to "try to extinguish the fire:' Taldng care of people is the first priority. After ensuring the occupants are safe, isolate the fire behind barriers such as doors. Then, sound the alarm to warn others and to notify the local fire department of the emergency. Finally, attempt to extinguish and contain the fire while waiting help. Posters containing these steps are often available from jurisdictional safety services. These posters should be located in areas with high visibility throughout the workplace as a reminder to employees in case of a fire emergency. As part of the safety orientation, employees are informed of the locations of the fire alarm pull stations and trained how to activate them. Power Engineers often receive firefighting training specific to the type of industry where they are employed, and are designated as first responders. For example, in a hospital or school they may be expected to be familiar with the building equipment and services (such as gas lines and electrical power), so when a fire occurs they know where to shut off the services. They may also participate in a number of tasks such as: a) How to reset pull stations. b) How to shut off sprinlder lines that have been activated when they are no longer required. c) How to attend to the fire alarm panels in the building and reset them, if necessary. d) How to determine from fire panels where fires are located or when a system is experiencing "trouble:' e) How to activate and deactivate fire alarm zones during construction or maintenance. f) How to service fire dampers. g) How to reset fire doors and smoke hatches. h) How to use fire hoses. 4-8 i) How to drain and roll up fire hoses that may have been used. j) How to use the various fire extinguishers available to fight fires. <(-------------------------------4-t_h_C_Ias_s_E_d_ii_l_on 3•_P __ ar_t_A ( Plant Fire Safety • Chapter 4 ================================ All jurisdictions across North America require regular fire drills, depending on the building occupancy, for the following reasons: ( a) To allow employees to practice and memorize fire response procedures. b) To assess and improve fire response procedures. c) To provide an opportunity to test the fire alarm system. Power Engineers must consult site-specific requirements. This also includes evacuation procedures. 4th Class Edition 3 • Part A 4-9