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Fire extinguisher Essay

The fire triangle or combustion triangle is a simple model for understanding the necessary ingredients for most fires. The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent (usually oxygen). A fire naturally occurs when the elements are present and combined in the right mixture and a fire can be prevented or extinguished by removing any one of the elements in the fire triangle. For example, covering a fire with a fire blanket removes the “oxygen” part of the triangle and can extinguish a fire.

To stop a combustion reaction, one of the three elements of the fire-triangle has to be removed. Without sufficient heat, a fire cannot begin, and it cannot continue. Heat can be removed by the application of a substance which reduces the amount of heat available to the fire reaction. This is often water, which requires heat for phase change from water to steam. Introducing sufficient quantities and types of powder or gas in the flame reduces the amount of heat available for the fire react in the same manner. Without fuel, a fire will stop. Fuel can be removed naturally, as where the fire has consumed all the burnable fuel, or manually, by mechanically or chemically removing the fuel from the fire. Fire stops because a lower concentration of fuel vapor in the flame leads to a decrease in energy release and a lower temperature. Removing the fuel thereby decreases the heat.

A fire extinguisher, flame extinguisher, or simply an extinguisher, is an active fire protection device used to extinguish or control small fires, often in emergency situations. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user (i.e., no escape route, smoke, explosion hazard, etc.), or otherwise requires the expertise of a fire department. Fire extinguishers can be classified into different types based on many factors: Fire extinguishers are divided into handheld and cart-mounted, also called wheeled extinguishers. Handheld extinguishers can weigh 1 to 30 pounds or more, and are easily portable by hand. Cart-mounted units typically weigh 50+ pounds. These wheeled models are most commonly found at construction sites, airport runways, heliports, as well as docks and marines. There are two main types of fire extinguishers in this type: stored pressure and cartridge-operated. In stored pressure units, the expellant is stored in the same chamber as the firefighting agent itself. Depending on the agent used, different propellants are used. Cartridge-operated extinguishers contain the expellant gas in a separate cartridge that is punctured prior to discharge, exposing the propellant to the extinguishing agent. This type is not as common, used primarily in areas such as industrial facilities, where they receive higher-than-average use.

Fire extinguishers are typically fitted in buildings at an easily-accessible location, such as against a wall in a high-traffic area. They are also often fitted to motor vehicles, watercraft, and aircraft- this is required by law in many jurisdictions, for identified classes of vehicles. All commercial vehicles must carry at least one fire extinguisher, with size depending on type of vehicle and cargo (i.e. fuel tankers typically must have a 9.1 kg, while most others can carry a 2.3 kg). The revised rule created criteria on the placement of “Fast Flow Extinguishers” in locations such as those storing and transporting pressurized flammable liquids and pressurized flammable gas or areas with possibility of three dimensional class B hazards are required to have “fast flow” extinguishers. Varying classes of competition vehicles require fire extinguishing systems, the simplest requirements being a hand-held portable extinguisher mounted to the interior of the vehicle.

A dry chemical agent called sodium bicarbonate. It is non-toxic, non-conductive and non-corrosive. It is easy to cleanup, requiring only vacuuming, sweeping or flushing with water. Extinguishers with sodium bicarbonate are usually used in residential kitchens, laboratories, garages, etc. Carbon dioxide removes oxygen to stop a fire but has limited range. It is environmentally friendly and leaves no residue, so cleanup is unnecessary. Extinguishers with carbon dioxide are usually used in contamination-sensitive places such as computer rooms, labs, food storage areas, processing plants, etc. A vaporizing liquid that is ozone friendly and leaves no residue. Because it requires no cleanup, fire extinguishers with halotron are ideal for computer rooms, telecommunication areas, theaters, etc. Foam floats on flammable liquids to tame the fire and helps prevent reflashes.

To cleanup the affected area, it must be washed away and left to evaporate. Fire extinguishers with foam are usually used in garages, homes, vehicles, workshops, etc. A dry chemical called potassium bicarbonate (K2CO3). It is non-conductive and non-corrosive. Clean up requires vacuuming, sweeping or flushing with water. Extinguishers with potassium bicarbonate are usually used in military facilities, oil companies, vehicles, etc. The most common agent is water; however, it cannot be used for class B or C fires because it is conductive. Water-based fire extinguishers are usually used in stockrooms, schools, offices, etc.

The potassium acetate based agent discharges as a fine mist which forms a soapy foam that suppresses any vapors and steam or the risk of fire reflash as it extinguishes the fire. Dry chemicals, CO2 and halon can be used on Class A fires, but may not be effective on their own. They need to be supplemented with water. ** Halon extinguishers are no longer made but some may still be in use. Dangerous gases are formed when halon is used to put out fires. Wear proper respiratory equipment, particularly in enclosed spaces. After use, do not allow anyone to enter the area until it has been well ventilated.

Fires are classified by the types of fuel they burn.

Class A Fires consist of ordinary combustibles such as wood, paper, trash or anything else that leaves an ash. Water works best to extinguish a Class A fire. Class B Fires are fueled by flammable or combustible liquids, which include oil, gasoline, and other similar materials. Smothering effects which deplete the oxygen supply work best to extinguish Class B fires. Class C Fires. Energized Electrical Fires are known as Class C fires. Always de-energize the circuit then use a non-conductive extinguishing agent. Such as Carbon dioxide. Class D Fires are combustible metal fires. Magnesium and Titanium are the most common types of metal fires. Once a metal ignites do not use water in an attempt to extinguish it. Only use a Dry Powder extinguishing agent. Dry powder agents work by smothering and heat absorption. Class K Fires are fires that involve cooking oils, grease or animal fat and can be extinguished using Purple K, the typical agent found in kitchen or galley extinguishers.

Unfortunately, there is not a universal fire extinguishing agent and therefore there is a possibility that using particular types of fire extinguishers on ignited materials or liquids may make the fire considerably worse and place the user at risk. To standardize the use of different extinguishers, fires have been divided into broad classifications for extinguishing purposes. This will assist in selecting the most effective fire-extinguishing agent to be used, on the most appropriate type of fire and burning material.

Depending on what type of flammable metals you are dealing with will decide which type of fire extinguisher you will require. The cheapest and most widely used fire extinguishers. Used for Class ‘A’ fires. Not suitable for Class ‘B’ (Liquid) fires, or where electricity is involved. More expensive than water, but more versatile. Used for Classes ‘A’ & ‘B’ fires. Foam spray extinguishers are not recommended for fires involving electricity, but are safer than water if inadvertently sprayed onto live electrical apparatus.

Often termed the ‘multi-purpose’ extinguisher, as it can be used on classes ‘A’, ‘B’ & ‘C’ fires. Best for running liquid fires (Class B). Will efficiently extinguish Class C gas fires. Carbon Dioxide is ideal for fires involving electrical apparatus, and will also extinguish class B liquid fires, but has NO POST FIRE SECURITY and the fire could re-ignite. Specialist extinguisher for class F fires.

For Metal Fires: A specialist fire extinguisher for use on Class D fires – metal fires such as sodium, lithium, manganese and aluminum when in the form of swarf or turnings.

The working of a Fire Extinguisher is rather very simple. At the top of the cylinder, there is a smaller cylinder filled with compressed gas. A release valve acts as a locking mechanism and prevents this gas from escaping. When you pull the safety pin and squeeze the lever, the lever pushes on an actuating rod which presses the valve down to open a passage to the nozzle. The compressed gas is released, applying a downward pressure on the fire-extinguishing material. This pushes the material out the nozzle with high amounts of pressure. Working of different types of extinguishers is explained below: Water extinguishers are filled with regular tap water and are typically pressurized with air.

The best way to remove heat is to dump water on the fire but, depending on the type of fire, this is not always the best option. Dry chemical extinguishers are filled with either foam or powder, usually sodium bicarbonate (baking soda) or potassium bicarbonate, and pressurized with nitrogen. Baking soda is effective because it decomposes at 158 degrees Fahrenheit and releases carbon dioxide (which smothers oxygen) once it decomposes. Dry chemical extinguishers interrupt the chemical reaction of the fire by coating the fuel with a thin layer of powder or foam, separating the fuel from the surrounding oxygen. CO2 extinguishers contain carbon dioxide, a non-flammable gas, and are highly pressurized. The pressure is so great that it is not uncommon for bits of dry ice to shoot out. CO2 is heavier than oxygen so these extinguishers work by displacing or taking away oxygen from the surrounding area. CO2 is also very cold so it also works by cooling the fuel.

A fire extinguisher typically deprives fire from oxygen. If you encounter a fire at home, on a stovetop, for example, you can smother the fire by putting a lid over your pan or pot. In some cases, you can toss a non-flammable chemical on the fire to reduce the combustion reaction. Good choices include table salt (sodium chloride) or baking soda (sodium bicarbonate). When baking soda is heated, carbon dioxide gas is given off, suffocating the fire. In this project, you’ll cause a chemical reaction to produce carbon dioxide gas. The carbon dioxide sinks in the air, displacing it and removing oxygen from the fire.

baking soda (sodium bicarbonate)
vinegar (weak acetic acid)
jar with lid, with hole in the lid.
Fill the jar about halfway full with vinegar.
To activate the fire extinguisher, drop in a spoonful of baking soda. Immediately shake the jar and point the hole of the jar toward your fire. Test out your fire extinguisher on a candle or small intentional fire so you will know what to expect.

If you want a directional fire extinguisher, you can insert a straw into the hole in the jar or bottle. Use caulk or tape to secure the straw so that it won’t shoot out of the jar when you use the homemade fire extinguisher.

Don’t add too much vinegar to the container! You want enough room to add the baking soda and to prevent excessive build-up of pressure. You can prepare sachets of baking soda for easier use. Simply wrap a spoonful of baking soda in a piece of tissue or toilet paper. When you’re ready to use the fire extinguisher, drop the packet of baking soda into the jar and close the lid.

For making the fire extinguisher shoot farthest, we apply a simple and basic chemistry equation i.e; IDEAL GAS Equation.
This equation is a simple equation to study the behavior different amount of gases under different temperature and volume. It states that
Product of Pressure and Temperature at a constant temperature is directly proportional to number of moles of the gas and its temperature i.e. PV=nRT
P is the pressure in the bottle
V is the volume of the bottle
n is the number of moles of gas in the bottle
R = Ideal Gas Constant
T = temperature Kelvin
We can increase the range by:
By Maximizing pressure by increasing the temperature and the number of moles of gas inside the bottle.

Solving for pressure or P, you get:
P = nRT / V
So, to maximize the amount of pressure and thus the distance you can shoot the carbon dioxide, you can: Minimize the volume of the container (V).
Maximize the amount of gas produced by the chemical reaction (n). Maximizing the temperature i.e. we can use vinegar at lukewarm temperature.

Home-made fire extinguisher is a non-rechargeable fire extinguisher while commercially used extinguishers are mostly rechargeable. Home-Made fire extinguisher which is shown, is a dry chemical fire extinguisher type using Sodium Bicarbonate and Vinegar but commercial ones can be of any type. Home-made fire extinguishers are intended for one time use only. If you use your home-made fire extinguisher even once, you must replace it. It will not be effective in fighting a fire. Commercial fire extinguishers are intended to be recharged once they are used, or when it loses pressure over time. Once a year or according to your local fire codes, fire extinguishers in business or commercial applications should be serviced by a certified fire equipment dealer, in accordance with the service manual and as identified on the fire extinguisher label. If it is discharged, commercial fire extinguisher must be refilled by a certified fire equipment dealer regardless of how much of the contents were used. Never test a fire extinguisher by using it.

Once used, it will gradually lose pressure and will not be fully charged for use in an emergency. Home-made fire extinguisher are always foam type fire extinguisher as they use CO2 as their extinguishing agent which is produced by the action of Baking Soda and Vinegar. Commercial fire extinguisher may be of any types mentioned above. Also, home-made fire extinguishers are always handheld while the commercial fire extinguishers may be handheld or the cartridge based. Home-made fire extinguishers can’t control the fire at a very high level. It can only control the small fires like kitchen fires etc. and if we use them for fires with high risk they may cause life risk to the user. For high risk fire, we must use a commercial fire extinguisher.

Apart from the efforts of myself, the success of any project depends largely on the encouragement and guidelines of many others. I take this opportunity to express my gratitude to the people who have been instrumental in the successful completion of this project. I would like to show my greatest appreciation to Prof.. I can’t say thank you enough for her tremendous support and help. Without her encouragement and guidance this project would not have materialized. Also, I am grateful to my friends who shared their knowledge with me and helped me in materializing my project. Last but not the least, I would like to thanks my parents and sister who were a constant support during my efforts. Thank you everyone.

Sunidhi Sharma
B.Tech. Computer Science
Roll No: 2013/368

Sites considered:
www.google.com
www.chemistry.about.com
www.ask.com
www.ehow.com
http://fireextinguishersinmetromanila.wikia.com
www.wikianswers.com
www.yahoo.com
www.openbookproject.com

Books:
Science and Life Textbook


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