The most widespread source of ignition was friction through the use
of a fire-drill or saw. In
such systems a small area is subjected to abrasive friction and heats to
form a hotspot, thermal transfer may then occur from the hotspot to the
system. In the case of the fire drill, friction between the drill tip and
the fire-board causes the formation of a hot charcoal-like dust. When this
hot dust is added to the dry tinder and blown the tinder may burn.
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