Question (science related)

apeZ · 21 Mar 2009 at 22:01

A little random, but I was thinking about this earlier...

If there is a fire, does it make a difference if you use hot or cold water to put it out?

Azagoth · 21 Mar 2009 at 22:03

Not really, you could use Heavy Water, Dideuterium monoxide, if you wanted and it'd still put the fire out. It all depends on what's ablaze though really.

V4NT0M · 21 Mar 2009 at 22:04

In theory cold water, in practice it doesn't really matter much.

The general idea of covering fire with water is that it is not flammable and suffocates the fire. I guess the hotter the water is the easier it would be for the fire to vaporise the water as it would take less energy and time for the water to turn to steam.

amirite?

Kristoph · 21 Mar 2009 at 22:08

I'm sure there's probably a balancing point somewhere.

It would depend entirely on:

Temperature of hot water (i.e. is it close to boiling point or near freezing?)
Quantity of water
Dispersion of the water as its sprayed or poured
Intensity of the fire

I'm sure there's a point at which the water *could* be near boiling point, lacking enough volume, far too dispersed, and just turned into steam or vapour.

I could be completely wrong though and everything above is rubbish.

MattandJet · 21 Mar 2009 at 22:08

Azagoth said:
Not really, you could use Heavy Water, Dideuterium monoxide, if you wanted and it'd still put the fire out. It all depends on what's ablaze though really.

Why stop there, go the whole hog!

Tritium monoxide!! (Super-heavy radioactive water!!) Lol

MattandJet · 21 Mar 2009 at 22:10

mp3kla said:
I'm sure there's probably a balancing point somewhere.

It would depend entirely on:

Temperature of hot water (i.e. is it close to boiling point or near freezing?)
Quantity of water
Dispersion of the water as its sprayed or poured
Intensity of the fire

I'm sure there's a point at which the water *could* be near boiling point, lacking enough volume, far too dispersed, and just turned into steam or vapour.

I could be completely wrong though and everything above is rubbish.

I would imagine cold water due to it needing energy to reach its specific heat capacity and it's high latent heat of vapourisation (Nerd words F.T.W)

which it could take from the fire's 'energy'

Kristoph · 21 Mar 2009 at 22:12

MattandJet said:
I would imagine cold water due to it needing energy to reach its specific heat capacity and it's high latent heat of vapourisation (Nerd words F.T.W) which it could take from the fire's 'energy'

Yeah I was just saying why hot water would be less effective.

thepeganator · 21 Mar 2009 at 22:14

Fire needs three things:

Heat, Oxygen, Fuel.

You need to take one away to stop a fire, CO2 takes oxygen away, water takes heat away.

Hotter water will take less energy to boil, and therefore evaporate quicker (therefore removing itself) and remove less heat, meaning you need more of it.

So colder water would be better.

Liquid *insert something non flammable and very cold here* would be better.

MattandJet · 21 Mar 2009 at 22:17

You can tell who does a science degree or are science-y minded

lol

Kristoph · 21 Mar 2009 at 22:17

thepeganator said:
Liquid *nitrogen* would be better

Kristoph · 21 Mar 2009 at 22:18

MattandJet said:
You can tell who passed their year nine science SATs lol

thepeganator · 21 Mar 2009 at 22:20

MattandJet said:
You can tell who does a science degree or are science-y minded lol

I do maths.

And I was going to put nitrogen, I wrote it an deleted it.

I couldn't remember if it was flammable or not and couldn't be bothered to be flamed.

MattandJet · 21 Mar 2009 at 22:20

SATs

lol

Well I like my science words, it makes me sound clever...ish

V4NT0M · 21 Mar 2009 at 22:20

thepeganator said:
Fire needs three things: Heat, Oxygen, Fuel.

Correct me if i'm wrong but fire does not need heat, it generates heat. I.e. you can light a fire in the depths of space al long as you have oxygen.

thepeganator · 21 Mar 2009 at 22:22

Skyfall said:
Correct me if i'm wrong but fire does not need heat, it generates heat. I.e. you can light a fire in the depths of space al long as you have oxygen.

Fire needs heat to sustain itself, if you cool it it stops.

But I think you are right in the fact that you don't need heat to start it, just some kind of spark/reaction.

Energize · 21 Mar 2009 at 22:22

You can put your hand in fire without being burnt depending on the source, cold water is better as it takes more energy to evaporate it.

Kristoph · 21 Mar 2009 at 22:23

MattandJet said:
I got Level 6 for year 9 SATs if I remember, this was about 5 years ago!

Thats out of 8 levels

I got 7 6 7. Bit above average iirc. 6 in English

MattandJet · 21 Mar 2009 at 22:25

mp3kla said:
Thats out of 8 levels

I got 7 6 7. Bit above average iirc. 6 in English

I meant year 6, I got 7 for the year 9 ones, but then I didn't really care about SATs - its not exactly going to be a decision maker in a job interveiw

lol

thepeganator · 21 Mar 2009 at 22:27

Energize said:
You can put your hand in fire without being burnt depending on the source, cold water is better as it takes more energy to evaporate it.

That's generally because of the time your hand is in there and the time is takes for your hand to heat up/feel the heat.

But yes, things like alcohol burn at a comparatively low temperature.

V4NT0M · 21 Mar 2009 at 22:29

thepeganator said:
Fire needs heat to sustain itself, if you cool it it stops.

But I think you are right in the fact that you don't need heat to start it, just some kind of spark/reaction.

Oh right I see what you mean... Sorry, as usual I'm crap at reading