It is an area of land isolated from surroundings having some frames and models for: 

( houses, cottages, trees, cars, … etc) , simulating an operation sector for training on:
evacuation, chasing, … etc.
These fields qualify trainees in conditions similar to expected operations. This is achieved by carrying out different scenarios for appearing of differing kinds of targets and following-up the trainee response and action.
All components of the field are completely protected against bullets-as it is designed for real fire