Intro | Test 1, 2, 3, 4 | Conclusions
This
lab investigates fire extinguishers. There are scientific processes that
make these extinguishers more efficient than other fire suppressants such
as water. However, in understanding how these extinguishers work, we found
that these are good alternatives to extinguishers around the house. One
important thing to note is that there are different types of fires:
Type A: Wood, Paper, Etc.
Type B: Flammable Liquids
Type C: Electrical
All of them are different, and one should note that only type A fires can be treated with water.
Also to understand these fires more we must know what fire is. It is a chemical combustion reaction that is a result of a fuel (wood, gas, etc.) that has reached its combustion temperature reacting with a gas like oxygen to combust. Woods combustion temperature is 260ºC.
Our experiments tested extinguishers against water to see how they worked for conventional purposes, but again, note that using water to put out type B fires is very unwise. Anyway, we did four trials, and ended up with our final results.
Test 1: Extinguishers with Type A Fires
We created a large fire with wood on a fire resistant surface and we let it grow until all of the wood was alight (1), we then began to spray it with the extinguisher (2) and after two or three seconds, the whole thing was out (3). One important effect to note is that right after the fire was put out, there was very little smoke (4), and the wood was not hot.
The way the extinguisher dealt with this was with monoammonium phosphate foam. This foam covers the fuel keeping it away from oxygen, while it decomposes to create carbon dioxide, which also acts as a barrier. The foam also enables the material to cool down. All told it acts quickly and prevents the fire from restarting after it is out.
Test 2: Water with Type A Fires
We created a similar fire again (2) and this time began to spray it with water (2) from a garden hose. It took longer than the extinguisher to put out (3) and still when the fire was out completely, there was a great deal of smoke and steam (4) and the wood remained hot.
The results showed that water was very effective against Type A fires, but the fact that the wood remained hot after the fire was put out showed that the fire could easily return because if the temperature of the wood rose, it could combust. This is often the case with large fires.
Test 3: Extinguishers with Type B Fires
This time we created a fire with gasoline only. The fire was rather violent at first so we would advise against doing this at home. To put it into perspective—we, the experts (cough! cough!)—had our own accident doing this test. Our gas can caught on fire, and the fire could have spread had we not put it out immediately. Liquid fires are dangerous because they can spread so make sure not to try one near any grass or vegetation. Keep it isolated because it can get messy. Anyway, once we got the fire burning it looked like this:
After we sprayed it with the extinguisher the fire went out very quickly and we were left only with the extinguisher’s foam. There was not heat and the gasoline was perfectly covered. The extinguisher proved very effective in this case.
Type 4: Water with Type B Fires
Water will not put out a liquid fire. It will often make the fire float on top and it will help spread it. We found that because the extinguisher is the best solution, if you need to put out a Type B fire and do not have one; you could use a similar technique. If you smother a fire with a heavy blanket or better yet Baking Soda it will go out. We would recommend baking soda as the best alternative to an extinguisher in this situation. It sounds crazy but it works. Anyway, to make this demo work we decided to use very little gas and a lot of water. We displaced the fire a bit, but put it out by smothering it with water. We would not recommend this technique though, so stick with the baking supplies.
A Note About Electrical Fires
Electrical fires are very dangerous and hard to contain. Never use water to fight them because you will get hurt. Water conducts electricity, and that is why some extinguishers can only treat them. When you buy an extinguisher for your house (which we recommend), we suggest that you make sure it covers Types A, B, & C.
When it came to Type A fires water and extinguishers seemed pretty equal. They took similar amounts of time, but the major point was that the extinguisher made sure that the fire did not come back. If you are dealing with a large fire, it is a different story though. It is hard to come across tons of foam, so here is how the fire department deals with Type A:
They use their pumper trucks to douse the fire with water, they wait until it is all out and then they use foam to prevent the fire from coming back. The biggest risk is for a fire scene to catch on fire again, so most fire trucks carry about 20 gallons of foam for this purpose.
For Type B the extinguisher won. Water should not be an option, so if you are out of luck you should use baking soda instead!
Finally remember, only treat a fire if it is small and you know what you are doing. We recommend that you buy an extinguisher, but we suggest that if the fire gets out of hand, leave as safely as possible and then contact your local fire department. They have the coolest equipment and they best know-how to make sure that you are safe and that the fire is contained.
Also if you buy an extinguisher make sure you know how to use it, put it in a readily available location, and check it often to make sure it is pressurized.
Cite
Our Experiments & Research
If you have used any of this information or any of these images
please go ahead and cite them in your bibliography. For your convenience,
this is what the citation would look like in MLA format:
Family, Afrooz. “Fire Extinguishers.” May 02, 2005 Mad Physics. dd mmm. yyyy †
<http://www.madphysics.com/exp/fire_extinguishers.htm">
We are glad to share our knowledge with you as long as you cite all of our info, and contact us before you use anything for non-educational purposes (commercial, etc.).
† In the bibliography you must insert the day you visited the site (this is relevant because the site could change at some point), therefore, in the bibliography above replace dd with the day you visited, mmm with the abreviated month, and yyyy with the year (ex: dd mmm. yyyy becomes 23 Dec. 2004).
