How Fire extinguishers work?:
A fire extinguisher is an device used to extinguish or control small fires, often in emergency situations. It is not designed, for use on an out-of-control fire, such as one which has reached the , endangers the user (i.e. no escape route, smoke, explosion hazard, etc.), or otherwise requires the expertise of a . Typically, a fire extinguisher consists of a handheld cylindrical containing an which can be discharged to extinguish a .
There are two main types of fire extinguishers: Stored pressure and generated pressure. In stored pressure units, the expellant is stored in the same chamber as the fire fighting agent itself. Depending on the agent used, different propellants are used. With dry chemical extinguishers, is typically used; water and foam are pressurized with air. Stored pressure is the most common types of fire extinguishers. Cartridge-operated extinguishers, contain the expellant gas in a separate cartridge that is punctured prior to discharge, exposing the propellant to the agent. These types as are not as common, used primarily in areas such as industrial facilities, where they receive higher-than-average use. They have the advantage of simple and prompt recharge, allowing an operator to discharge the extinguisher, recharge it, and return to the fire in a reasonable amount of time. Unlike stored pressure types, these extinguishers utilize compressed instead of nitrogen, although nitrogen cartridges are used on low temperature (-60 rated) models. Cartridge operated types are available in dry chemical and dry powder in the US and water, wetting agent, foam, and dry powder (ABC, BC, or D) in the rest of the world.
Fire extinguishers are further divided into handheld and cart-mounted, also called wheeled extinguishers. Handheld extinguishers weight from 2 to 30 pounds (1 to 14 kilograms), and are hence easily portable by hand. They exist in both stored- and generated-pressure types and contain all types of suppressants. Cart-mounted units typically weigh 50+ pounds (23+ kilograms), are cartridge-operated, and typically contain either dry chemical, , foam, Halon, Halotron-1 or CO2. Wheeled models are most commonly found at , , , and temporary landing sites.
Classification:
Fire needs fuel, oxygen and heat in order to burn. In simple terms, fire extinguishers remove one of these elements by applying an agent that either cools the burning fuel, or removes or displaces the surrounding oxygen.
Fire extinguishers are filled with water or a smothering material, such as CO2. By pulling out the safety pin and depressing the lever at the top of the cylinder (the body of the extinguisher), this material is released by high amounts of pressure.
How it Works
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.
Although the temptation is to aim the extinguisher at the flames, the proper way to use the extinguisher is to aim it directly at the fuel.
Water Extinguishers
Water extinguishers are filled with regular tap water and pressurized with oxygen. 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
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.
Carbon Dioxide (CO2) extinguishers
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.
FIRES:
Fire is the and released during a , in particular a . Depending on the substances alight, and any impurities outside, the of the and the fire's might vary. Fire in its most common form can result in , and has the potential to cause physical damage through .
Fires start when a and/or a material with an adequate supply of or another is subjected to enough and is able to sustain a . This is commonly called the . No fire can exist without all of these elements being in place.
Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of in the process of and may propagate, provided there is a continuous supply of an and .
Fire can be by removing any one of the elements of the fire tetrahedron. Fire extinguishing by the application of water acts by removing heat from the fuel faster than combustion generates it. Application of is intended primarily to starve the fire of oxygen. A forest fire may be fought by starting smaller fires in advance of the main blaze, to deprive it of fuel. Other gaseous fire suppression agents, such as or , interfere with the chemical reaction itself.
A flame is an , self-sustaining, oxidizing chemical reaction producing and glowing hot matter, of which a very small portion is . It consists of reacting gases and solids emitting visible and light, the of which depends on the chemical composition of the burning elements and intermediate reaction products.
In many cases, such as the burning of , for example wood, or the incomplete of gas, solid particles called produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue colour due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but burning in also produces a flame, producing (HCl). Other possible combinations producing flames, amongst many more are and , and and .
The glow of a flame is complex. is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also emission by de-excited and in the gases. Much of the radiation is emitted in the visible and bands. The colour depends on temperature for the black-body radiation, and on chemical makeup for the . The dominant colour in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, the fire is white, the hottest colour possible for organic material in general, or yellow. Above the yellow region, the colour changes to orange, which is cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.
The (NASA) of the has recently found that plays a role. Modifying the gravity causes different flame types. The common distribution of a flame under normal gravity conditions depends on , as soot tends to rise to the top of a general flame, as in a in normal gravity conditions, making it yellow. In , such as an environment in , convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although it will go out if not moved steadily, as the CO2 from combustion does not disperse in microgravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs. Experiments by NASA reveal that in microgravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behave differently in microgravity when compared to normal gravity conditions. These discoveries have potential applications in and , especially concerning .
In combustion engines, various steps are taken to eliminate a flame. The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such as .
Typical temperatures of fires and flames:
flame: 9000 or above (3645 °F)
flame: 1300 to 1600 °C (2372 to 2912 °F)
flame: 1,300 °C (2372 °F)
flame: 1000 °C (1832 °F)
:
Temperature without drawing: side of the lit portion; 400 °C (750 °F); middle of the lit portion: 585 °C (1110 °F)
Temperature during drawing: middle of the lit portion: 700 °C (1290 °F)
Always hotter in the middle.
Temperatures of flames by appearance:
The temperature of flames with carbon particles emitting light can be assessed by their colour:
Red
Just visible: 525 °C (977 °F)
Dull: 700 °C (1290 °F)
Cherry, dull: 800 °C (1470 °F)
Cherry, full: 900 °C (1650 °F)
Cherry, clear: 1000 °C (1830 °F)
Orange
Deep: 1100 °C (2010 °F)
Clear: 1200 °C (2190 °F)
White
Whitish: 1300 °C (2370 °F)
Bright: 1400 °C (2550 °F)
Dazzling: 1500 °C (2730 °F)
services are provided in most developed areas to extinguish or contain uncontrolled fires. Trained use , water supply resources such as and or they might use A and B class foam depending on what is feeding the fire. An array of other equipment to combat the spread of fires.
Fire prevention is intended to reduce sources of ignition, and is partially focused on programs to educate people from starting fires. Buildings, especially and , often conduct fire drills to inform and prepare citizens on how to react to a building fire. Purposely starting destructive fires constitutes and is a criminal offence in most jurisdictions.
Model building require and systems to minimize . The most common form of active fire protection is . To maximize passive fire protection of buildings, and in most developed countries are tested for , and . , and used in and are also tested.
Fire blankets:
Fire blanket is a safety device designed to extinguish small incipient (starting) . It consists of a sheet of fire retardant material which is placed over a fire in order to smother it
Small fire blankets, for use in kitchens and around the home, are usually made of , and are folded in to a quick-release container for ease of storage.
Larger fire blankets, for use in and industrial situations, are often made of (sometimes treated with a flame retardant fluid). These blankets are usually mounted in vertical quick-release cabinets so that they can be easily pulled out and wrapped round a person whose clothes are on fire.
Some older fire blankets were made of woven fibre. This can pose a hazard during the decommissioning of old equipment.
How fire blankets work:
In order for a fire to burn, all four elements of the must be present: heat, fuel, oxygen and a sustaining chemical chain reaction. A fire blanket either completely surrounds a burning object or is placed over a burning object and sealed closely to a solid surface around the fire. Whether the blanket is placed on top or surrounding it, the job of the blanket is to cut off the oxygen supply to the fire, and put it out.
In using a fire blanket, it is important to protect the hands; the picture at the top of this page shows the correct procedure, in which the blanket is folded around the hands to protect them from the heat whilst it is applied.
