Fire extinguishers-principles of operation and factors affecting their efficient use

Introduction: (Initial Observation)

Fire is very useful; however, when it gets out of control, our only hope for survival and saving our belongings is in having necessary knowledge and skills to control it.

Proper knowledge of controlling fire can save lives and prevent expansion of fire in emergencies.

To control fire, you must know what material are flammable, what material are fire retardant and what material are fire extinguisher. Many flammable, fire retardant and fire extinguisher substances may be found around your home. In this project you will study fire extinguishers and fire extinguisher materials that may be found at home. Compare different household liquids or solids for their ability to extinguish fire.

Safety Warning: The experiments of this project require adult supervision and a fire safe environment (Open space is prefered). You must be away from any possible combustible material while performing fire related experiments.

Information Gathering:

Find out about fire extinguishers and how they work. Read books, magazines or ask professionals who might know in order to learn about different fire extinguisher material that are used in fire extinguishers. Keep track of where you got your information from.

Following are samples of information that you may find:

Fire Extinguisher is a portable device used to put out fires of limited size. Such fires are grouped into four classes, according to the type of material that is burning.

Class A fires include those in which ordinary combustibles such as wood, cloth, and paper are burning.

Class B fires are those in which flammable liquids, oils, and grease are burning.

Class C fires are those involving live electrical equipment.

Class D fires involve combustible metals such as magnesium, potassium, and sodium.

Each class of fire requires its own type of fire extinguisher.

Standards for the selection, placement, and testing of portable fire extinguishers are issued by the National Fire Protection Association, a nonprofit technical and educational organization in Quincy, Massachusetts. The standards establish the minimum requirements for all types and sizes of extinguishers that are listed and rated by testing laboratories against standard test fires of the types they are designed to control. Each extinguisher is rated as to both type and size of the fire extinguished. For example, a 20-B extinguisher should extinguish a flammable-liquids fire that is 20 times the size of a fire that an extinguisher rated 1-B would extinguish. Extinguishers that cannot extinguish the minimum size test fires are not listed or rated. Some extinguishers will put out only one class of fire; others are used for two or even three classes; none is suitable for all four classes.

Fire extinguishers may go unused for many years, but they must be maintained in a state of readiness. For this reason, periodic inspection and servicing are required, and that responsibility rests with the owner. Fire department inspectors check at periodic intervals to see that extinguishers are present where required by law and that they have been serviced within the specified time period.

I. Extinguishers for Class A Fires

Class A fire extinguishers are usually water based. Water provides a heat-absorbing (cooling) effect on the burning material to extinguish the fire. Stored-pressure extinguishers use air under pressure to expel water. Pump-tank extinguishers are operated by a hand pump.

III. Extinguishers for Class B Fires

Class B fires are put out by excluding air, by slowing down the release of flammable vapors, or by interrupting the chain reaction of the combustion. Three types of extinguishing agents—carbon dioxide gas, dry chemical, and foam—are used for fires involving flammable liquids, greases, and oils. Carbon dioxide is a compressed gas agent that prevents combustion by displacing the oxygen in the air surrounding the fire. The two types of dry chemical extinguishers include one that contains ordinary sodium or potassium bicarbonate, urea potassium bicarbonate, and potassium chloride base agents; the second, multipurpose, type contains an ammonium phosphate base. The multipurpose extinguisher can be used on class A, B, and C fires. Most dry chemical extinguishers use stored pressure to discharge the agent, and the fire is extinguished mainly by the interruption of the combustion chain reaction. Foam extinguishers use an aqueous film forming foam (AFFF) agent that expels a layer of foam when it is discharged through a nozzle. It acts as a barrier to exclude oxygen from the fire.

IV. Extinguishers for Class C Fires

The extinguishing agent in a class C fire extinguisher must be electrically non-conductive. Both carbon dioxide and dry chemicals can be used in electrical fires. An advantage of carbon dioxide is that it leaves no residue after the fire is extinguished. When electrical equipment is not energized, extinguishers for class A or B fires may be used.

V. Extinguishers for Class D Fires

A heat-absorbing extinguishing medium is needed for fires in combustible metals. Also, the extinguishing medium must not react with the burning metal. The extinguishing agents, known as dry powders, cover the burning metal and provide a smothering blanket.

The Underwriters’ Laboratories, Inc., has available lists of approved fire extinguishers that may be purchased from different manufacturers. The extinguisher label gives operating instructions and identifies the class, or classes, of fire on which the extinguisher may be used safely. Approved extinguishers also carry the labels of the laboratories at which they were tested.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

This is a sample question for fire extinguishing studies:

How do different beverages affect a class A fire? Can we use beverages to extinguish fire? How do they compare with water in extinguishing class A fires?

This is another possible question for fire extinguisher project:

How do different household powders such as salt, baking soda, sand and powder detergents compare in their ability to extinguish class A fires?

Note that adults and higher grade students may try similar experiments on class B, C or D fires.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

This is how you may define variables for the first question.

Independent variable (also known as manipulated variable) is the type of beverage.

Dependent variable (also known as responding variable) is the effect of the beverage in extinguishing fire.

Controlled variables are temperature and wind.

Constants are the source, the type and the size of fire as well as the experiment procedures.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis:

I hypothesize that among beverages, carbonated water has the highest effect on extinguishing water. Carbonated water contains CO2 gas that can stop fire by depriving it from oxygen. Beverages with alcohol, sugar and other organic material such as fruit juices may increase the fire or reduce the fire at a lower rate.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Introduction: In this experiment you compare different beverages or household liquids for their abilities to extinguish a class A fire. Use a spray bottle to simulate the action of a fire extinguisher.

Procedure:

1. Prepare some same size and identical combustible sets for your experiment. You need one set for each of the liquids that you need to test. A combustible set can be a combination of one or more combustible material such as charcoal, cardboard, wood and some fire starter fuel.
2. Fill up a spray bottle with a sample of the liquid that you want to test. Adjust the nozzle so it can spray to a distance of about 3 feet.
3. Weigh the bottle with it’s content and record it.
4. Light up one set and wait for 30 seconds so it gets hot.
5. Spray the liquid from the distance of 3 feet on a constant pace until you extinguish the fire.
6. Weigh the bottle again and calculate the amount of liquid used to extinguish the fire. Record it in your results table.
7. Repeat the steps 2 to 6 with each of the liquids that you need to test. Records your results in a table like this:

Liquid name	Initial bottle weight	Final bottle weight	Consumed liquid
Water
Carbonated Water
7Up
Apple Juice

You may try any other household liquids or beverages of your choice. Do not try solvents and alcoholic beverages that may increase the fire.

Make a graph:

Make a bar graph to visually demonstrate the results of your experiments. Make one vertical bar for each of the liquids that you test. The height of each bar represents the amount of one liquid used to extinguish fire. The most effective extinguisher liquid is the one that you use the least amount of that to extinguish fire.

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Experiment 2:

In this experiment you compare different household powders for their ability to extinguish a class A fire. Use a can with holes at the top as a sprinkler of the powders.

Procedure:

1. Prepare some same size and identical combustible sets for your experiment. You need one set for each of the liquids that you need to test. A combustible set can be a combination of one or more combustible material such as charcoal, cardboard, wood and some fire starter fuel.
2. Fill up a can or a jar with a sample of the powder that you want to test. Close the lid. (the lid must have holes so you can sprinkle the powder over the fire.)
3. Weigh the can with it’s content and record it.
4. Light up one set and wait for 30 seconds so it gets hot.
5. Sprinkle the powder from the distance of 3 feet on a constant pace until you extinguish the fire.
6. Weigh the can again and calculate the amount of powder used to extinguish the fire. Record it in your results table.
7. Repeat the steps 2 to 6 with each of the powders that you need to test. Records your results in a table like this:

Liquid name	Initial bottle weight	Final bottle weight	Consumed liquid
Sand
Salt
Starch
Baking soda

You may try any other household powder of your choice. Do not try powders that are known to be flammable.

Make a graph:

Make a bar graph to visually demonstrate the results of your experiments. Make one vertical bar for each of the powders that you test. The height of each bar represents the amount of one powder used to extinguish fire. The most effective extinguisher powder is the one that you use the least amount of that to extinguish fire.

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Experiment 3: Construct a CO2 fire extinguisher

Introduction: Class A, B and C fires can be extinguished with carbon dioxide gas. There are two types of carbon dioxide fire extinguishers. One type contains compressed carbon dioxide gas and the other contains chemicals that can react and produce carbon dioxide gas when needed. In this experiment you will construct a carbon dioxide fire extinguisher that use a chemical reaction to produce CO2 gas.

Procedure:

Fill up a bottle up to a third with baking soda.

Fill up a balloon (without inflation) with vinegar.

Attach the balloon to the mouth of the bottle as shown in the picture. Use a string to secure the balloon in place.

slowly lift the balloon so the vinegar can gradually enter the bottle.

Balloon starts to inflate. Wait until the balloon is fully inflated. Tie another string on the neck of the bottle and untie the one that holds the balloon on the top of the bottle.

Now you should have a balloon filled with carbon dioxide.

Test your balloon as a fire extinguisher. How effective it is for different types of fire.

Materials and Equipment:

Material used for this experiment include:

1. Charcoal, paper, cardboard or other combustible material
2. Lighter fluid (may be required to start the fire)
3. Matches or lighter
4. Samples of beverages (or any other substance that you may want to test for its ability to extinguish fire)
5. Samples of household powders such as salt, baking soda
6. Metal container to hold the fire during the experiment.
7. Fire safe place for experiments
8. Adult supervision

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

Description

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

http://www.ilpi.com/safety/extinguishers.html

http://www.hanford.gov/fire/safety/extingrs.htm