I can't quite find a category for this so forgive me for using this one. Can any one advise on the seemingly arbitrary approach to fire safety measures required in buildings of varying heights. I fully understand that taller buildings come with increased risk but the requirements seem to be extreme as one transitions from one height to another. For example, a building of height 17.999m might require 60 min fire resistance but one at 18.01m requires 90. 

They are arbitrary figures and if you convert them to floors less than 18m is about 6 floors reaching about halfway up the 7 Floor, above 18 m will be 8 floor so dealing with fractions of a metre is not called for.

Also fighting a fire in an a building eight storeys or more, has to be fought from inside the building, because the availability of ariel appliances and their capability are limited and I believe the extra protection is needed.