Have you ever thought that it was odd that paper is reputed to burn at 451 degrees Fahrenheit? Doesn’t that seem a little high? After all, we’ve all seen how quickly and easily paper can burn when exposed to a match, right? So, why does it appear to be so hard to burn when we look at that number? It has to do with the fact that there are a few ways to define “burning” as we found out for you.
The temperature at which paper will burn can vary by material, moisture, and thickness. The average temperature at which it will ignite and burn is between 424 and 475 degrees Fahrenheit (218 and 246 degrees celsius).
Let’s take a closer look at the proposed burning temperature of paper and see what they look like in the real world. We will also explore how cardboard’s burning/ignition temperatures compare to those of paper.
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The Burning Temperature of Paper
Before we get too deep into this – we need to acknowledge that different types of paper will have substantially different numbers associated with them. The age of the paper may also cause a variation in the burning temperature of the paper too.
So, we’ve tried, wherever possible, to take an average between different types of paper for this article, but that isn’t a measure of increased accuracy – it’s a ballpark figure.
This only really matters if you’re trying practical experiments to force paper to burn, something that we wouldn’t recommend trying outside of a lab environment with plenty of fire safety equipment on hand. Otherwise, you may find that the exact numbers are less of a problem than the fire, that you just started, is.
But then we also need to acknowledge that there are several definitions that we might apply to the term “burn” when asking, “At what temperature does paper burn?” These include:
- The temperature at which a naked flame can set the paper on fire.
- The temperature at which paper “just” catches fire by itself (spontaneously).
- The temperature which burning paper gives off or produces.
These numbers are not the only possible definitions, changing the atmospheric pressure around a fire, for example, can also impact on these temperatures.
But unless you intend to light a fire on top of Everest or at the bottom of the Marianas Trench, in most environments such changes are minimal at best and don’t offer a significant impact on the figures generated.
By this, we mean at “what temperature can a naked flame or spark set the paper on fire?” as opposed to paper just sitting around getting warmer before it goes up in smoke à la Ray Bradbury.
Well, nearly any naked flame ought to do the trick but mainly because most naked flames are very hot in the first place. They may have a very localized heat in that you can place your fingers an inch or two above or to the side of the flame and keep them cool but place your finger in the hottest burning area of the flame and you’ll regret it.
The hottest area of a flame is not the tip of the flame but the slight “blue” aura around it, this is the zone in which the material being burned is undergoing a process of absolute combustion (that is all the material is being burned and thus, releasing the maximum amount of energy).
This blue aura is more visible with some flames than others but it is always there.
Typical temperatures from a naked flame include 4,074 degrees from a Butane cigarette lighter, 1670 degrees from a candle, and 3,488 for an ethanol (alcohol) flame!
It becomes very clear when we do this exercise that the heat of a naked flame is considerably higher than the auto-ignition temperature of paper. That is the temperature at which paper catches fire all by itself.
Also read: Is Fiberglass Flammable or Fire Resistant?
So, Ray Bradbury’s claim of 451 degrees Fahrenheit belongs here and to be fair to the master of science fiction – in his day, this was the number that was most widely believed to be true.
He couldn’t have known that his book about the burning of books (and thus, the title “Fahrenheit 451”) would catch on so well that the number would become permanently associated with the temperature that paper combusts at.
However, all the modern evidence says that Bradbury’s number is probably a little on the low side. In particular, old textbooks (of the kind burned in Bradbury’s book) seem to burn at around 481 degrees Fahrenheit. That’s not a huge difference but it is significant enough to be interesting.
This does not mean that if you throw a book into an oven at this temperature that it immediately bursts into flame.
Paper is an insulator and thus, at least to begin with, it will absorb quite a bit of heat and the peculiar density of paper in the center would ensure that heat was funneled away from the surface of the outside pages – which are the only bit that can catch fire because they need a fuel source, oxygen in the air, to burn.
So, it will take a few minutes but when it happens, the book ought to go up in a few seconds and then over a minute or two, it should be reduced entirely to ash as long as the temperature remains constantly higher than 481 degrees Fahrenheit. Of course, the act of burning the book will help with this as burning a book releases heat.
Take a look here:
Note: We would also like to offer an outlying opinion on this temperature, from the Handbook of Physical Testing of Paper, Volume 2 by Borch et al. This unusual journal suggests that paper combusts at around 475 – 550 degrees celsius! That’s a lot hotter than 481 degrees Fahrenheit.
However, they also say they are using paper made from Cotton and Rayon. Given that most paper is made of wood pulp, we are leaving this information as an interesting side note and sticking with our assertion that most paper combusts at 481 degrees Fahrenheit.
How much heat does the burning of a book release? Well, a lot.
While a book may go up in flame at 481 degrees Fahrenheit, it most certainly doesn’t burn at that temperature. In fact, it burns much hotter still, rather like our naked flames (which a burning book is) the temperature can get very high, indeed.
We’d estimate that the hottest part of a paper fire, assuming that nothing had been done to the environment to increase the temperature, would be around 1,600 degrees Fahrenheit! More than enough to keep our oven getting warmer as the book burns.
Also read: How Hot Does Wood Burn? Examined
Ignition Temperature Of Cardboard
The ignition temperate of “corrugated board” which is the official definition of what cardboard is, is much higher than that of paper. This is something that we think ought to be obvious given that cardboard is a heavier, more dense material and can thus insulate against heat more effectively than paper.
The number we have for this is 800 degrees Fahrenheit, which is over 300 degrees more than paper requires! So, if you want to pick an insulating material from paper and cardboard, go with cardboard.
Also read: What Makes Something Flammable?
At what temperature does paper burn? Well, it depends on how you define burn but if we go with Ray Bradbury’s definition the probable answer is that paper auto-ignites at around 481 degrees Fahrenheit though that number is subject to significant variance and one study, though something of an outlier, claims that it’s really 481 degrees Celsius! (We don’t agree.)
As for how hot paper gets when it burns? The answer is very hot, indeed, with temperatures of up to 1,500 degrees Fahrenheit being nothing outside of the normal range. With the right conditions and fuel, it’s possible that they could become much, much hotter still.