Medieval towns were frequently destroyed by fire. What information in this spread helps to explain why this happened?

Four main things

1) Buildings were made of combustible materials - timber - and usually heated by open fires
2) Narrow streets with jettied construction on upper floors meant that fire spread easily from one building to another
3) No running water, fire brigade or fire fighting provision - eg no sprinklers.
4) No legilslation to control how buildings were constructed.

Even if we were inclined to do your homework, we don't HAVE this spread you are supposed to refer to in your answer.