Remember the main aim of the FDR1 is to provide statistics and the categories are fairly broad.
The amount of detail will also depend on the Brigade and the person filling it in and checking it. At one time the officer checking the FDR1s in my brigade would reject it if the wording did not comply with the guidance given, hence when filling in the FDR1 we looked at the guidance and put the nearest we could find. OK it didn't reflect the actual circumstances but the FDR1 didn't come back!
Also remember an FDR1 is filled in for every fire, so look at the number of fires in a year every one has an FDR1 and it took a good half hour to fill the form in.
So as an OiC I've just got back from a fire tired,hot, sweaty and wanting a brew, I have to get the crews organised to sort out and replenish the pumps then keep them occupied while I fill in this ***** form. This is not going to be an objective scientific dissertation.