Week 4-Fire Hazards and Controls PDF

# Welcome to: Fire Hazard and Controls ## Upon completion of this module, you should be able to: ### Remember - Identify the three elements of the fire triangle. - Define the flammability parameters: lower flammability limit, upper flammability limit, flashpoint temperature, and autoignition temp...

# Welcome to: Fire Hazard and Controls ## Upon completion of this module, you should be able to: ### Remember - Identify the three elements of the fire triangle. - Define the flammability parameters: lower flammability limit, upper flammability limit, flashpoint temperature, and autoignition temperature. ### Understand - Explain how each flammability parameter provides insight into the fire hazard and risk of a material or process. ### Apply - Identify and classify fire hazards in given examples. ### Evaluate - Determine prevention and mitigation controls for targeting each side of the fire triangle. # Topic 1: The Basic Principles of Fire ## Fire and Humans - Of all the species on Earth, humans alone have learned to produce, maintain, and control fire. - Scientists estimate that early humans learned to control fire over one million years ago. - Early humans' ability to use fire changed the course of human evolution, allowing humans to cook food, stay warm, have light for work and socializing, ward off predators, and create new tools. - Fire has been an integral part of human development and human history. - Sometimes fire is controlled and useful, such as a candle providing light or a fire in a woodstove providing warmth. - But other times, fire is uncontrolled and destructive. - Throughout history, fire has destroyed cities and killed thousands. - Fire has changed the urban landscape of several major cities. For example: - In 1666, much of the City of London was destroyed by a fire that is believed to have started in a baker's shop. - In 1871, the Great Chicago Fire killed 300 people and destroyed more than 17,000 buildings across 2,000 acres in under 30 hours. - Today, fire continues to make headlines, destroying property, damaging businesses, and claiming lives: - On Feb 20, 2003, 100 people died when fire erupted in The Station Nightclub in West Warwick, Rhode Island. - On March 25, 2018, an estimated 60 people died in a fire at a shopping mall in Kemerovo, Siberia. - On June 14, 2017, fire broke out in the 24-story Grenfell Towers apartment building in London killing 71 people. ## The Definition of Fire - If you were asked to describe fire, you might speak of flickering orange flames, glowing embers, and radiating warmth. But what is fire really? - Scientists define fire as a chemical reaction where a fuel combines with an oxidant and releases energy, part of which is used to sustain the reaction. This type of reaction is referred to as combustion. - In general, combustion reactions can be thought of as: $Fuel + Oxidant → Combustion products + Energy$ - This relationship can be described visually by the fire triangle. For a fire hazard to exist, all three elements of the fire triangle must be present: - Fuel - Oxidant - Ignition Source ## The Fire Triangle - The fire triangle is a simple model for understanding the chemical reaction that must take place for fire to ignite. - Let's look at each element of the fire triangle in more detail. ### Oxidant - An oxidant is an agent that removes electrons (oxidizes) from other reactants in a specific type of chemical reaction called a redox reaction. Combustion is a type of redox reaction. - Oxidants are oxygen-rich or oxygen-like materials. - Examples of oxidants include: - Solid: peroxides, perchlorates. - Liquid: liquid oxygen, hydrogen peroxide. - Gas: oxygen gas (pure or in air), chlorine gas, fluorine gas. ### Ignition Source - An ignition source is a source of potential energy, in the form of heat, that can start a combustion reaction. - Heat is also needed to maintain the fire and enable it to spread. - Ignition sources can include any material, equipment, or operation, that emits a spark or flame or radiates heat. - Examples of ignition sources: - Sparks: starting a camp fire. - Lightning: natural starting of forest fires. - Hot surfaces: grease catching fire on a stovetop. - Flames: lighting a birthday candle. ### Fuel - A fire requires fuel to ignite. - Fuel is any oxygen deficient material that can undergo a combustion reaction. - The moisture content, size, shape, and quantity of the fuel will determine how easily it will burn and at what temperature. - Examples of fuel include: - Solid: candle wax, wood, coal, metal powder. - Liquid: acetone, pentane, gasoline. - Gas: hydrogen, acetylene, propone, natural gas. ## Exercise One - Sort the following items into three groups according to which element of the fire triangle they correspond to: - Wood - Gasoline - Oxygen gas - Hydrogen peroxide - Sparks in an electric switch - A hot lightbulb ## Exercise Two - Please read the following scenario: - A container of motor oil is sitting on a shelf in the storage shed behind a house. - There is a hole in the bottom of the container, and oil is leaking out of the container and off the edge of the shelf. - The homeowner has just finished mowing the lawn and wheeled the lawnmower into the shed, placing it under the shelf. - The lawnmower's casing is still hot. ### Question 1 - Which elements of the fire triangle are present in this scenario? Check all that apply: - Fuel. - Oxidant. - Ignition source. ### Question 2 - Is there a fire hazard? - Yes. - No. # Topic 2: Flammability Parameters ## Flammability Parameters - Different materials present different levels of fire hazard. - The degree of fire hazard a material poses depends on the material's specific chemical properties, includng: - Lower flammability limit. - Upper flammability limit. - Flashpoint temperature. - Autoignition temperature. ## Flammability Limits and Range - Flammability is the ability of a material to ignite and burn. - A gas or vapour will burn when an ignition source is present only if the fuel vapour concentration is within a specific range. - The concentration is generally expressed as percent of fuel by volume. - The upper and lower limits of this range are referred to as the flammability limits or explosive limits. - If there is too little or too much fuel vapour, the reaction mixture cannot burn. - The flammable range is the range of fuel vapour concentrations where a fire can occur. - The flammability limits of a gas are usually reported in air (21% oxygen) at 20°C and at atmospheric pressure, but can be found for any concentration of oxygen. - Flammability limits in pure oxygen are important for some applications, such as medical treatments where pure oxygen is supplied to patients. - For more information about flammability limits and the ranges of some common laboratory solvents, refer to McGill University's Environmental Health and Safety Unit's Laboratory Safety Manual. ## Lower Flammability Limit - The Lower Flammability Limit (LFL) is the lowest concentration of fuel vapour at which a fire can occur. - At this concentration the fuel vapour is also described as being "too lean" to burn even if a source of ignition is present. - LFL can be measured experimentally. - It can also be estimated as the concentration where oxygen in air provides half the stoichiometric amount of oxygen (i.e. the amount of oxygen required for complete combustion). ## Upper Flammability Limit - The Upper Flammability Limit (UFL) is the highest concentration of fuel vapour at which a fire can occur upon contact with a source of ignition. - Above this concentration the fuel vapour is also described as "too rich" to burn. - This means there is not enough oxygen in the air-vapour mixture. - UFL of a gas can be measured experimentally. - It can also be estimated as the concentration where oxygen in air provides three-and-a-half times the stoichiometric amount of oxygen. ## Saturation Vapour Pressure - If a liquid is placed in a closed container, after time some of the liquid particles will evaporate. - In other words, they will leave the liquid phase and enter the gas phase, occupying the space above the liquid. - Eventually, some of these gaseous particles will return to the liquid phase. - So there is movement both ways: liquid <=> vapour. - When the number of particles moving from liquid to gas phase and gas to liquid phase is equal, the two phases are in equilibrium. - In a closed container, the gaseous particles exert a pressure against the walls of the container. - The pressure is the saturation vapour pressure. - The concentration of the vapour when vapour and liquid are in equilibrium is indicated by the saturation vapour pressure curve on the adjacent graph. - Notice that as temperature increases the saturation vapour pressure increases ## Flashpoint Temperature - The flashpoint temperature is the lowest temperature at which a liquid evaporates to form an ignitable mixture with air. - The flashpoint temperature provides us with useful information about the possiblity of a liquid forming a flammable mixture of vapour with air. - The lower the liquid's flashpoint temperature, the easier it is to ignite. - To protect against a fire hazard when working with liquids, it is important to know the liquid's flashpoint. - The risk of a fire occurring is lower for a process that takes place at a temperature below the flashpoint temperature than for a process that takes place at a temperature above the flashpoint. - The flashpoint temperature can be determined experimentally, but it can also be estimated as the intersection of the LFL with the saturation vapour pressure curve. ## Flammable versus Combustible Liquids - The National Fire Protection Association classifies liquids in terms of their flashpoint: - Flammable liquid: A liquid with a flashpoint temperature below 38°C (100°F). - Combustible liquid: A liquid with a flashpoint temperature above or equal to 38°C (100°F). - So while both flammable and combustible liquids can burn, in general flammable liquids will ignite and burn easily at normal working temperatures, while combustible liquids burn at temperatures that are usually above working temperatures. ## Autoignition Temperature - Autoignition temperature is the lowest temperature at which a vapour-and-air mixture can ignite without the presence of an ignition source, such as a spark or flame. The mixture ignites spontaneously from the energy of the environment. - The fire triangle still applies in this situation: fuel and oxidant must both be present for a fire to erupt. In autoignition, however, the ignition source is the energy from the high temperature. - Autoignition can occur in a couple of different ways, including self-heating and adiabatic compression. ### Self-heating hazard - Oily rags left in a garbage container can catch fire without an external source of ignition. How does this happen? - The oil on the rags is exposed to air and slowly oxidizes. This reaction releases heat that accumulates faster than it dissipates. The heat causes the temperature to rise to the autoignition temperature and the rags may ignite spontaneously.. - The self-heating process is a greater hazard for liquids with low vapour pressure.. - Conversely, for liquids with high vapour pressure the heat is removed quickly by evaporative cooling before the temperature rises to the autoignition temperature. ### Adiabatic compression ignition - Adiabatic compression refers to an abrupt increase in temperature as a result of a rapid increase in pressure. - When a gas is compressed quickly, the heat that is generated cannot be released into the environment quickly enough, and the temperature of the gas rises significantly. - If the gas is a fuel-air mixture in the flammable range and the heating increases the gas temperature above the autoignition temperature, the mixture can combust. - Adiabatic compression ignition is a hazard associated with air compressors - If the compressor inlet gas includes flammable vapours, a fire could result. - Adiabatic compression ignition is also the process at work in diesel engines. # Topic 3: Hazard Control and the Fire Triangle ## Hazard Control and the Fire Triangle - We can reduce the risk associated with fire hazards by intentionally including control measures in our processes. - These controls can target all three sides of the fire triangle: fuel, ignition and oxidant. - Federal and provincial legislation exists that addresses fire controls. - Pertinent legislation and regulations can be found in provincial and national codes such as: - The National Building Code of Canada 2015. - National Fire Code 2015 - Canadian Electrical Code - In addition, many provinces follow the codes and standards of the National Fire Protection Association (NFPA). ## The Hierarchy of Controls and Fire Hazards - The Hierarchy of Controls is a way of thinking about controlling risk. - It describes five methods for controlling risk arranged in order of decreasing effectiveness: ### Elimination - Elimination is the most effective way to control hazards. - If the hazard no longer exists, then the risk no longer exists. - Eliminating a hazard ensures everyone and everything is safer. ### Inherent Safety - An inherently safer design is one that permanently eliminates or reduces hazards, to avoid or reduce the consequences of incidents. - A process can be made inherently safer using one of four inherently safer design principles: - Minimization: Minimization means reducing the amount of a hazard that is present. - Substitution: Substitution is the replacement of a hazard with a lesser hazard. - Moderation: Moderation refers to using a less hazardous form of a hazard. - Simplification: Simplification means operating around a hazard in as easy and direct a manner as possible, thus minimizing the probability of errors. ### Engineering Controls - Engineering controls are systems added on to a process in order to prevent or mitigate a loss of containment. - A loss of containment event occurs when the energy corresponding to the hazard is released in an unwanted way. ### Administrative Controls - Administrative controls are controls that reduce risk by instructing how work must be done safely. - They include activities such as training, and written rules and procedures for how to act when around hazards. ### Personal Protective Equipment - Personal protective equipment is equipment that a worker wears to protect themselves from hazards. - It is the final item on the hierarchy of controls. ## Fuel Controls - All fires need fuel to ignite, which is why it is one of the elements of the fire triangle. - Any oxygen-deficient material-solid, liquid or gas-that can undergo a combustion reaction is a potential fuel source. - By controlling the fuel source, we can control the fire hazard. ### Elimination - According to the Hierarchy of Controls, the most effective control we could put in place to reduce the risk of a hazard is one that eliminates the hazard altogether. - Without fuel, the fire triangle collapses and a fire cannot start. ### Inherent Safety and Engineering Controls - It is not always or even often possible to eliminate fuel from a process. - However, we may be able to make a process inherently safer by minimizing the fuel or substituting it for something less hazardous: - Minimize the amount of fuel present at a location and store it in enclosures where oxidants are not present. - The NFPA standard and other building codes contain detailed guides for the storage of fuel that is less hazardous. ## NFPA Standards - The NFPA has spent decades thinking about and learning from fire incidents with the goal of improving the safety of designs. - The Association publishes over 300 codes and standards that are intended to minimize the risk and effects of fire. - These comprehensive standards cover the design, installation, maintenance and operation of a wide range of systems. - Most Canadian fire codes are based on the NFPA standards. ### NFPA standards for fuel storage - The NFPA recommends storing fuels in minimal quantities and in enclosures where oxidants are not also stored. - NFPA-30 standard, the Flammable and Combustible Liquids Code, includes detailed information on the design of fuel storage facilities of all sizes. - The standard lists the requirements for the maximum size of small portable containers used by a single worker, to relief venting and minimum ventilation rates for large underground storage bunkers. ## Oxidant Controls - All fires need an oxidant to ignite. - It is another element of the fire triangle. - The most common oxidant is oxygen in air (Air contains approximately 21% oxygen.) ### Reduction of Oxidants - Like fuel controls, controls that target the oxidant side of the fire triangle are aimed at preventing flammable-range conditions to form. - Oxidant controls prevent these conditions from forming by removing oxygen, thus reducing the range of vapour concentrations that result in a flammable mixture. ### Use of Inert Gases - One control method for reducing the concentration of oxygen uses inert gases and is referred to as "inerting." - Inert gases, also known as noble gases, do not react with many substances, which makes them very useful in certain situations. - In the inerting process, an inert gas is introduced into a confined space to displace the oxygen. - Because of the oxygen present in air, inerting can only be applied to a closed system. - Inert gases used in this process include: - Carbon dioxide. - Nitrogen. - Argon. - Helium. - Steam and flue gas. ## Inerting as a Hazard Control - There are four methods commonly used for replacing oxygen with an inert gas. - The method used depends in part on the type of vessel or container being used. ### Method 1: Vacuum inerting - Vacuum inerting is the most common inerting method. - It is used only on vessels that have been designed to withstand vacuum pressure. - The procedure is relatively simple but slow: a vacuum is drawn on the vessel, then the vessel is refilled with an intert gas. - This process is repeated until the desired concentration of oxidant is reached. ### Method 2: Pressure inerting - In this method, the inert gas is added under pressure to the vessel's maximum design pressure, then the vessel is vented down to operating pressure. - This process is repeated until the desired oxidant concentration is reached. - Positive pressure inerting avoids some of the hazards associated with vacuum inerting by increasing the pressure in the vessel and then venting to a lower pressure, instead of drawing the pressure below ambient with a vacuum pump. - Pressure inerting can only be used on vessels rated to operate at pressures above atmospheric. - Pressure inerting also introduces hazards related to pressure vessels, venting of high-pressure gases, and inert atmosphere hazards, such as asphyxiation hazards. ### Method 3: Sweep through inerting - As the name implies, in this procedure, gas is introduced into a vessel at one opening, and mixed gas is withdrawn from another opening. - The sweep through procedure is commonly used for vessels or equipment that is not rated for pressure or vacuum. ### Method 4: Siphon inerting - The siphon inerting procedure involves filling the vessel with a liquid such as water, or any other liquid compatible with the product, then adding the inert gas as the liquid is drained from the vessel. ## Ignition Controls - The third element of the fire triangle is ignition. - Sources of ignition are a challenge to completely eliminate, but we can take measures to minimize ignition hazards. - Open flames, hot surfaces, and static electricity are common ignition hazards that we can control: ### Flames - Flames are present in boilers, furnaces, and many welding operations (referred to as hot work). - Open flames should be extinguished whenever the other two sides of the fire triangle, i.e. fuel and an oxidant, may be present in an area. ### Hot surfaces - Hot surfaces can occur on electrical heaters, overheated equipment, and short-circuited electronics or result from the friction of two surfaces rubbing together. - We can control these hazards by thoroughly inspecting equipment and performing regular maintenance. ## Static Electricity: An Ignition Hazard - Static electricity results from an imbalance between positive and negative charges (electrons) in an object. - These charges can build up on the surface of the object until they are released. - If one surface has a surplus of negative charges compared to another surface, then an electrical potential (voltage) exists between the two surfaces. - If the charge difference is large enough, when these two surfaces are brought close together, the negative charges will flow from the surface with more charges to the surface with fewer charges creating a spark. - A common example of static electricity in action occurs when you walk across a carpet in your sock feet then touch a metal door knob and get a shock. - When you walked across the carpet, you collected electrons. The electrons clung to you until toughed the door knob. Because the door knob has a lower charge, the electons flowed from you to the knob. - A common industrial example occurs when a non-conductive fluid such as gasoline is pumped through a non-conductive tube such as a plastic hose. - To protect against static buildup, flammable liquid dispensing systems are designed to be bonded and grounded. ### Bonding - Electrical bonding is the practice of connecting all metallic, non-current carrying objects using a protective bonding conductor to ensure the objects are at the same potential. - In the example of the gas containers, a metal conductor electrically connects the supply and target containers so that any difference in voltage that accumulates is equalized by charge flowing through the conductor instead of a spark. ### Grounding - Electrical grounding refers to the practice of connecting an electrical circuit to the ground. - Any excess current traveling through the circuit is absorbed by the ground. - In the example of the gas container, the container is grounded to prevent it from forming a voltage difference with its surroundings. - The container is connected with a metal conductor to the ground so that voltage is equalized by charge flowing through the conductor instead of a spark. ## The National Electric Code Categories - All electrical systems, from transformers and breakers to cell phones and smart watches, can cause sparks. - The NFPA has established standards to reduce the risk of fire or explosion occurring due to sparks from electrical systems. - The NFPA-70 standard, also known as the National Electrical Code, classifies areas with possible fire or explosion risk due to the presence of explosive gases or mixtures as hazardous (or classified) locations or areas and categorizes these areas into classes and divisions. - Class: Defines the general nature of the hazardous material in the surrounding atmosphere. - Division: Defines the probability of hazardous material being present in the surrounding atmosphere. - A hazardous area is described in terms of both Class and Division. - For example, an area might be Class I, Division 2 or Class II, Division 1. - Engineers use this classification system to determine whether the electrical systems in an area must be explosion proof, i.e. specially designed so that if a spark occurs inside an electronic device, the ignited flames cannot spread outside of the device. ## Self Check - At this point in the module, you should be able to: - Describe the flammability parameters: lower flammability limit, upper flammability limit, flashpoint temperature, and autoignition temperature. - Explain how each flammability parameter provides insight into the fire hazard and risk of a material or process. - Identify and classify fire hazards in given examples. - Describe the prevention and mitigation controls for targeting each side of the fire triangle. - The following questions are intended to help you monitor your own learning. - You must determine the correct answer for each question in order to proceed, but you may make multiple attempts. - If you have difficulty answering these questions, review the content in this section before continuing. ### Question 1 - It is recommended that a flammables cabinet for storing pentanes and hexanes contain a maximum of 45 gallons of liquids. - None of these liquids should be peroxides. - Which side(s) of the fire triangle does this design control? - Fire - Fuel - Oxidant - Ignition Source ### Question 2 - A system for transferring petroleum products from a rail car to a storage tank requires that a metal cable be clipped to the rail car and the storage tank. - Which elements of the fire triangle does this design control? - Fire - Fuel - Oxidant - Ignition Source # Module Summary - You have reached the end of this module. - You should now be able to: - Identify the three elements of the fire triangle. - Define the flammability parameters: lower flammability limit, upper flammability limit, flashpoint temperature, and autoignition temperature. - Explain how each flammability parameter provides insight into the fire hazard and risk of a material or process. - Identify and classify fire hazards in given examples. - Determine prevention and mitigation controls for targeting each side of the fire triangle. - You can review the course content anytime by accessing the course menu. - If you are ready to take the module exam, click the 'Complete' button below to close this module and access the exam.