5
$\begingroup$

I think most have heard the advise that you should put flour (or baking soda) on a grease fire to absorb the oil before. While this is certainly better than using water, I'm skeptical.

For starters it is know that flour is excellent at demolishing flour mills, but in these instances it is a dust explosion (actually a deflagration) in a confined space versus a splash of mostly unaerated powder onto a fire. Even the fine particles that fall off should only cause mild flames compared to the on going grease fire. The main cause of skepticism is the potential charring of the flour releasing water and causing splattering (i.e. bigger fire).

Alternatively baking soda has been suggested, but this also seems dodgy as it starts to decompose at 50 °C releasing carbon dioxide and water, and how many people have enough baking soda to fill a pan in their kitchen ready to go? It seems that a lid would be the most appropriate response and of course would not recommend someone to do their own fire fighting if not prepared to do so, but when seconds count help is only minutes away.

I suppose that decomposition would be less of an issue if sufficiently slow kinetically. But debating physical sciences is a fools errand so I ask: Is flour or baking soda really suitable for extinguishing grease fires?

$\endgroup$
  • $\begingroup$ Not sure about flour, but baking soda definitely sounds good. Its decomposition is precisely why is it good. $\endgroup$ – Ivan Neretin Oct 12 '18 at 14:59
  • 1
    $\begingroup$ If the flour is coarse, it might be OK. But if it's very fine and powdery, you might just be making a very flammable aerosol, depending on how you deliver it. $\endgroup$ – Zhe Oct 12 '18 at 15:09
  • $\begingroup$ Putting on a lid is the best solution. Soda decomposes not at 50, but 1600°C. No chance of that happening, but if it did, it would, as you say, release CO2, which is also fine. You might have a larger supply of table salt in your kitchen, an excellent fire extinguisher. If none of the above is at hand, a kg of wheat flour serves the same purpose, at the cost of a bit more of a mess to clean up afterwards. $\endgroup$ – Karl Oct 12 '18 at 20:14
  • $\begingroup$ Id have to look up the composition of flour, but unless the stipulation of grease fire has a caveat im unaware of... the decomposition of baking soda is good for two reasons off the top of my head. 1. It's a heat sink. Energy absorbed from the fire is energy that doesnt go into sustaining the chain reaction of combustion (ie. the fire) after ignition. NaCl salt is used similarly (against class D metal fires i believe). 2. Evolving CO$_2$ gas displaces the air around the fire and insulates it from oxidation by O$_2$ in the air. This use of CO$_2$ is a common mechanism for fighting fires. $\endgroup$ – Blaise Oct 12 '18 at 23:32
1
$\begingroup$

The reason these substances are advocated for is to quickly remove the oxygen source from the burning oil. The lids to the pan is a great option, but if the flames are too high, someone might struggle to get the lid on.

The idea with a powder substance is to dump a bunch on, beating down the fire, then continue to fight it. Now put the lid on. If all the flames are out, you can add water to cool the mixture, perhaps, but be careful.

The main point is to have something other than water to reduce the flames. Yes, it will make a mess, but it will buy a little time by cutting off the oxygen supply.

$\endgroup$
  • $\begingroup$ Don't put water on it until everything has cooled well below 100°C! Pull the pan off the hot plate, extinguish the flames with lid, salt, soda, or whatever you have at hand, and wait. $\endgroup$ – Karl Oct 12 '18 at 20:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.