Hi Steve
I'll try to answer this the best I can with your description and I will try to put it in layman's terms. The legislation says that a responsible person must ensure that the workplace is safe from fire fore employees and anyone else in or around the premises. The employer is normally the responsible person, but, if there are multiple employers on a building then it may fall to the owner of the whole premises. It is the responsible persons responsibility to have a fire risk assessment carried out and this would determine what fire extinguishers are required and when and how often fire drills are required.
if this explanation is not enough ask a supplementary question(s).
Bob