Questions related to fire:
What is fire?
Why does smoke come from fire?
What should you do in case of a fire?
"Should I Try to Fight this Fire?"
What are the classes of fires?
What is fire?
Fire is a chain reaction between different elements. In order to have fire three elements must be present: Fuel, something which will burn, heat and oxygen.
Fires occur when something flammable like wood or plastic, the fuel, come in contact with enough heat to begin breaking down some of its cellulose materials. These cellulose materials then begin to release volatile gases known as smoke. Once the gases are hot enough they begin to combine with oxygen creating a flame and starting a fire. The fire will then continue to burn until one or more of the elements are removed.
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Why does smoke come from a fire?
(Excerpt taken from howstuffworks.com)
Let's say you have a nice fire going, and it has burned down to the point where what you see is a collection of hot "glowing embers." The fire is still producing a lot of heat, but it is producing no smoke at all. You might have gotten to this point either by starting with logs in a fireplace or by starting with charcoal. If you now toss a piece of wood, or even a sheet of paper, onto this fire, what you will notice is that the new fuel produces a lot of smoke as it heats up. Then, all of a sudden (often with a small pop), it bursts into flame and the smoke disappears.
If you have a fireplace or wood stove, or if you have been around a lot of campfires, this little scene is very familiar to you, and it tells you a lot about smoke -- let's look at what is happening.
There are four things that you find in any piece of wood:
- Water - Freshly cut wood contains a lot of water (sometimes more than half of its weight is water). Seasoned wood (wood that has been allowed to sit for a year or two) or kiln-dried wood contains a lot less water, but it still contains some.
- Volatile organic compounds - When the tree was alive, it contained sap and a wide variety of volatile hydrocarbons in its cells. Cellulose (a chief component of wood) is a carbohydrate, meaning it is made of glucose. A compound is "volatile" if it evaporates when heated. These compounds are all combustible (gasoline and alcohol are, after all, hydrocarbons -- the volatile hydrocarbons in wood burn the same way).
- Carbon
- Ash - Ash is the non-burnable minerals in the tree's cells, like calcium, potassium and magnesium.
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What should you do in case of a fire?
In case of a fire you should ACTIVATE and ASSIST then ATTEMPT.
ACTIVATE the building alarm system or notify the fire department by calling 911.
ASSIST any persons in immediate danger or those incapable of exiting the building on their own, making sure there is no immediate risk to yourself.
ATTEMPT to extinguish the fire.
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When should you consider fighting a fire?
Before you ever consider fighting a fire you should first:
- Call 911 and report the fire
- Make sure the building is being evacuated
- Make sure YOU have a safe path to an exit
Key factors you should consider/know when fighting a fire:
- Know how to properly use a fire extinguisher
- Make sure the fire will not block your exit from the building
- Determine that the fire extinguisher available is the proper type for the fire
- Determine whether the fire is too large or is spreading
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What are the classes of fires?
There are five different classes of fires:
Class “A” - Common combustibles such as wood, cloth, paper and rubber.
Class “B” - Flammable liquids such as gasoline, oil, grease and oil-based paint.
Class “C” - Electrical fires, those involving energized electrical equipment such as wiring, fuse boxes, circuit breakers, machinery and appliances.
Class “D” - Flammable metals such as magnesium, sodium, potassium or lithium.
Class “K”- Fires involving vegetable oils, animal oils or fats in high temperature cooking appliances; commercial kitchens require a Class K Fire Extinguisher.
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Questions related to fire extinguishers:
How do multi-class dry chemical fire extinguishers work?
Why are there various fire extinguisher sizes?
Are there different types of fire extinguishers?
What are the limitations of fire extinguishers?
Using an Extinguisher? Remember P.A.S.S.
How do multi-class dry chemical fire extinguishers work?
In order to put out any fire you need to remove one of the three elements; either, the fuel, heat or oxygen. Dry chemical fire extinguishers are by far the most common fire extinguishers in the home. They can handle all three types of potential fires found in a kitchen or workshop: combustible solids like wood or paper, combustible liquids like gasoline or grease, and electrical fires. The idea behind a dry chemical fire extinguisher is to blanket the fuel with an inert solid (similar to dirt or sand). A dry chemical extinguisher sprays a very fine power of sodium bicarbonate (normal baking soda), potassium bicarbonate (nearly identical to baking soda), or ammonium phosphate. These solids coat the fuel and smother the fire.
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Why are there various fire extinguisher sizes?
Portable fire extinguishers have various ratings to determine the size and type of fire they can handle. This rating is expressed as a number from 1 to 40 for Class A fires and from 1 to 640 for Class B fires. This rating will appear on the label-- 2A:10B:C, for example. The larger the numbers, the larger the fire of a specific class on which the extinguisher can be used. No number accompanies an extinguisher's Class C rating. The C on the label indicates only that the extinguisher is safe to use on electrical fires. Extinguishers for Class D fires must match the type of metal that is burning. These extinguishers do not use numerical ratings. Extinguishers for Class D fires are labeled with a list detailing the metals that match the unit's extinguishing agent.
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What are the different types of fire extinguishers?
There are different types of fire extinguishers, the type of extinguisher must be appropriate for the type of fire being fought. Multi-purpose fire extinguishers, labeled ABC, may be used on all three classes of fire. If you use the wrong type of extinguisher, you can endanger yourself and make the fire worse. Depending on their intended use, portable extinguishers store specific extinguishing agents. The types of fire extinguishers include:
- Pressurized Water Models are appropriate for Class A fires only. These must never be used on electrical or flammable-liquid fires.
- Carbon Dioxide extinguishers contain pressurized liquid carbon dioxide, which turns to a gas when expelled. These models are rated for Class B and C fires, but can also be used on a Class A fire. Carbon dioxide does not leave a residue.
- Dry Chemical extinguishers are either stored-pressure models or cartridge-operated models. They are usually rated for multiple purpose use and the dry chemicals leave a residue that must be cleaned up after use. These include: Ammonium Phosphate extinguishers for Class A, B and C fires; Sodium Bicarbonate extinguishers for Class B and C fires; Potassium Bicarbonate, Urea-Base Potassium Bicarbonate and Potassium Chloride for Class B and C fires.
- Foam (AFFF and FFFP) extinguishers coat the surface of a burning flammable liquid with chemical foam. When using a foam extinguisher, blanket the entire surface of the liquid to prevent oxygen from reaching it.
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What are the limitations of fire extinguishers?
Portable extinguishers are not designed to fight large or spreading fires. Even against small fires, they are useful only under certain conditions:
- The operator must know how to use the extinguisher.
- The extinguisher must be within easy reach, in working order, and fully charged.
- The extinguisher must match the type of fire being fought. (Extinguishers containing water are unsuitable for use on grease or electrical fires.)
- The extinguisher must be large enough to put out the fire. Many portable extinguishers discharge completely in as few as eight to ten seconds.
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Using an Extinguisher? Remember P.A.S.S.
Although there are many different sizes and types of fire extinguishers they all work in relatively the same way. Always keep your back to an unobstructed exit, stand six to eight feet away from the fire, and follow the PASS four-step procedure.
PASS --- Pull – Aim – Squeeze – Sweep
Pull the pin - This unlocks the operating lever and allows you to discharge the extinguisher. Some extinguishers may have other lever-release mechanisms.
Aim low - Point the extinguisher nozzle (or hose) at the base of the fire.
Squeeze the lever above the handle - This discharges the extinguishing agent. Releasing the lever will stop the discharge. (Some extinguishers have a button instead of a lever.)
Sweep from side to side - Moving carefully toward the fire, keep the extinguisher aimed at the base of the fire and sweep back and forth until the flames appear to be out. Watch the fire area. If the fire re-ignites, repeat the process.
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Questions related to smoke detectors:
How Do Photoelectric Smoke Detectors Work?
How Do Ionization Smoke Detectors Work?
How Do Photoelectric Smoke Detectors Work?
All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120-volt house current.
Inside Photoelectric smoke detectors there is a light and a sensor, but they are positioned at 90-degree angles to one another, like this: In the normal case, the light from the light source on the left shoots straight across and misses the sensor. When smoke enters the detection chamber of the smoke detector, the smoke particles scatter the light and some amount of light hits the sensor. The sensor then sets off the horn in the smoke detector. Photoelectric detectors are better at sensing smoky fires, such as a smoldering mattress.
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How Do Ionization Smoke Detectors Work?
(Excerpt taken from about.com)
Ionization detectors have an ionization chamber and a source of ionizing radiation for detecting smoke. The source of ionizing radiation is a minute quantity of americium-241 (perhaps 1/5000th of a gram), which is a source of alpha particles (helium nuclei). The ionization chamber consists of two plates separated by about a centimeter. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the americium knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber.
The positively-charged oxygen and nitrogen atoms are attracted to the negative plate and the electrons are attracted to the positive plate, generating a small, continuous electric current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The drop in current between the plates triggers the alarm.
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The staff at St. Cloud Fire Equipment receives many questions related to fire, fire prevention and fire protection. We have provided answers to some of the more common questions.