https://en.wikipedia.org/wiki/Fahrenheit_451

The title page of the book explains the title as follows: Fahrenheit
451—The temperature at which book paper catches fire and burns.... On
inquiring about the temperature at which paper would catch fire,
Bradbury had been told that 451 °F (233 °C) was the autoignition
temperature of paper.[32][33] In various studies, scientists have
placed the autoignition temperature at a range of temperatures between
424 and 475 °F (218 and 246 °C), depending on the type of
paper.[34][35]

https://en.wikipedia.org/wiki/Fahrenheit_451

Fahrenheit 451 is a 1953 dystopian novel by American writer Ray
Bradbury.[4] It presents an American society where books have been
personified and outlawed and "firemen" burn any that are found.[5] The
novel follows Guy Montag, a fireman who becomes disillusioned with his
role of censoring literature and destroying knowledge, eventually
quitting his job and committing himself to the preservation of
literary and cultural writings.

==================

question - why doesnt paper burn at 300 degrees or 200 degrees? - that
is pretty warm

my guess is that the answer lies within the chemical concept of
"activation energy" - iirc the energy required to run a chemical
process requires a large amount at the beginning but lesser amounts
later on - on a graph this shows as a big bump on a chart - iirc that
is where the term 'activation energy' is rooted

lets google it!