A train that can do only 50 mph is being overtaken by a fire moving at 70 mph along a straight track with...

real-life/train.fire

Problem

A train that can do only 50 mph is being overtaken by a fire moving at
70 mph along a straight track with nothing ahead; what can you do to
save the train?

You are on a train travelling at 50mph heading North on a straight
track.  That particular track does not bend for hundreds of miles ahead
and behind.  You hear on the radio that there is a big fire breaking
from South of where your position is.  This blazing fire is travelling
North at the speed of 70mph.  You also hear from the reliable
forecasters that the wind speed will remain at 70mph for the next 4
hours.  You go up to the engineer of the train and you calculate with
him that at the rate that this fire is travelling, it will catch up
with the train in approx. 3.5 hours.  If it does catch up, you are
guaranteed to be burned with all the occupants of the train since the
train also carries a load of petroleum.  If you stop the train, you
have one hour before the 70mph fire catches up.  And by then you cannot
run very far.  There are no towns, rivers, roads or other rail tracks
ahead (within the 3.5 hour travel distance).  The maximum speed of
this train even when reducing the number of cars to one, is 50mph.
Calling for help won't do, because all the train's transmitters don't
work.  The fire is expected to catch up and burn everything in it's
way.  There is only one thing you can do to save the whole train with
it's occupants.  What do you do?

The puzzle may be fictitious, but the answer is real.

-- Sam Mehsen <smehsen@pms086.pms.ford.com>

Show solution

Start a second fire ahead of the train, and drive the train onto the
ground it has burned.

Stop the train, go a little way north of the engine, and set the
grass and brush on both sides of the track alight.  The 70 mph wind
drives this new fire north, away from the train, at the same speed as
the big fire, and it leaves behind a strip of burned-out ground with
nothing left to burn.  Once the ground just ahead has burned off, move
the train forward onto it, well inside the burned strip, and stop
(the new fire outruns the train, 70 mph against 50, so the train never
catches it).  When the big fire arrives at the south edge of the strip
it finds no fuel and dies there, or at worst burns past on the
flanks, while the train sits on bare ground.  There is time: a
stopped train has an hour before the fire arrives, and a fire running
at 70 mph clears a long strip in minutes.

That is the "real" part.  It is an "escape fire": in the Mann Gulch
fire in Montana on 5 August 1949, the smokejumper foreman Wagner Dodge,
with the fire racing uphill behind his crew, lit the grass in front of
him and lay down in the burned area as the main fire passed over; he
survived.  His men did not follow him into it, and thirteen of them
died.  Norman Maclean told the story in "Young Men and Fire"
(1992).  The related technique of burning out fuel in front of an
advancing fire ("backfiring", "burning out") is standard in
firefighting.
-- Claude (rec.puzzles Oracle, 2026-11-02)