Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How water, CO2, sand etc extinguish fire?

  1. Jan 12, 2015 #1
    Well all answer this basic question by saying that water decreases the heat energy of fire, CO2 blocks O2 from reaching fire.But what about coke, higher molecular gases.
     
  2. jcsd
  3. Jan 12, 2015 #2

    Doug Huffman

    User Avatar
    Gold Member

    There are fuels which combustion will not be prevented by particular extinguishers.

    I once had to watch a beautiful little race car burn completely to ashes for the proper fire extinguisher being too far away to arrive in time. The car spun out, rolled the tire off the magnesium wheel which ignited and spread to the magnesium engine block and transmission.
     
  4. Jan 12, 2015 #3
    Then what is the reason for fire being extinguished when wind blows. There is more amount of oxygen in air then CO2. So it should burn?
     
  5. Jan 12, 2015 #4

    Doug Huffman

    User Avatar
    Gold Member

    Fire extinguished by a current of N2 and O2 is due to cooling. Remember combustion as a triangle of necessity, fuel, oxidant, and heat.

    I was a state certified fire control technician in California (Sixties) and Georgia (Eighties). I certified in Georgia specifically to provide automobile race track-side assistance.
     
  6. Jan 12, 2015 #5
    That doesn't seem so sound.When wind blows how it cools? It may be hot air. Then by your logic still air must also extinguish fire?
     
  7. Jan 12, 2015 #6

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Well, what about coke? This is a substance with a high percentage of elemental carbon, i.e., it's a fuel. No one tries to extinguish a fire by adding more fuel to it.

    Which 'higher molecular gases' are you talking about? (This term is unclear)

    Water extinguishes many types of fires because it 1) keeps oxygen away, and 2) it cools the burning material by absorbing heat.

    However, water should not be used to extinguish a grease fire, for example, because it will disperse the burning grease, possibly creating additional fires, and because grease floats on water, which allows the fire continued access to oxygen.
     
  8. Jan 12, 2015 #7
    Sorry . I am talking of coke(drinkable) like Pepsi or diet coke. Gases like SO2 or there are many gases except organic ones.
     
  9. Jan 12, 2015 #8

    Doug Huffman

    User Avatar
    Gold Member

    The result of adding water to a grease fire is a spectacular and common demonstration at firefighting schools.

    A half-full drum of oil is ignited and self-heated to a rolling boil. Then a liter of water at the end of a long manipulator is plunged into the boiling oil, flashes to steam and launches a large fire ball.

    A lesson shortly following has the training structure (concrete, multi-level, grated decks, drains, emergency flooding capability) flooded with fuel and the trainee hose team is directed to wait until the fuel is well ignited and enter. The hose is spun to splash the fuel and flames away and everyone huddles around the nozzle for the fresh cool air entrained in the water stream. I'm still impressed fifty years later. I first served on an ammunition ship, USS Paricutin AE-18 (so old that my mother remembered grinding on it).
     
  10. Jan 12, 2015 #9

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Unlike CO2, sulfur dioxide is capable of further combustion to form SO3. Sulfur oxides are also capable of forming choking fumes which can incapacitate anyone unfortunate enough to breathe these gases, even in concentrations not sufficient to asphyxiate. SO3, when it comes into contact with water or moisture, turns into sulfuric acid.

    Soft drinks can be used to extinguish a fire in a pinch, but this is a very expensive way. Although carbonated beverages contain small amounts of dissolved CO2, when this gas comes out of solution, there is generally not enough of it to provide a sufficient displacement of oxygen to starve the fire. The water from the beverage would be the extinguishing agent.
     
  11. Jan 12, 2015 #10
    So is there any liquid other than water, a economical one which can extinguish fire and any gas for the same other than CO2? How does wind extinguish small range fire? The number 4 post of Doug Huffman did not seem so sound.
     
  12. Jan 12, 2015 #11

    Bystander

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Not a whole lot of things come to mind.
    Nitrogen will suffocate and cool most fires. Do the job in a pinch.
    The same way you blow out candles or matches, by cooling the flame before it can transfer heat to the fuel. That's if "range" means stove/cooking appliance. If "range" means prairie/steppe/grassland, the heat is transferred down wind to other fuel, and you've got problems.
     
  13. Jan 12, 2015 #12
    But the wind could be hot. I know it would be relatively less hot than flame but then still air which sometimes might be cooler than wind must also extinguish fire?
     
  14. Jan 12, 2015 #13

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Wind is actually an enemy to controlling wild fires big and small. In addition to bringing more oxygen to the flames, changes in wind direction can cause a fire to change direction suddenly, potentially trapping firefighters or others in places which put them at risk from being injured or killed by the fire.

    At one time, a gas called Halon 1301 was used instead of CO2 to smother fires in enclosed spaces, like the engine rooms of ships. Because it was in a class of chemical compounds similar to CFCs, its use was banned by the Montreal Protocol because it damaged the ozone layer of the atmosphere.

    http://www.facilitiesnet.com/firesa...-Fire-Suppression-Systems-Were-Banned--10300#

    There are several other fire suppression systems which use a variety of different gases:

    http://en.wikipedia.org/wiki/Gaseous_fire_suppression
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How water, CO2, sand etc extinguish fire?
  1. Fire+water = ? (Replies: 9)

Loading...