To me it sounds like the building being dicussed has been converted into private self-contained flats. This is different from an HMO, where some facilities are shared (that is a very general definition of an HMO but will do for now, before anyone gets excited).
The usual difference between flats and HMOs from a fire safety perspective is that flats are seperate fire compartments, and thus a fire in one should not (in theory) affect the others. Therefore means of escape is based on the occupants of only one flat escaping, whilst the occupants of the others can stay where they are, possible unaware of the inferno next door. This is similar to what you would expect for, say, a row of terrace houses. Each one is a single dwelling in its own right.
With HMOs it is common to have a lower standard for fire resistance, and therefore it is normal for all occupants of the entire house to escape at once.
So, back to the original point. The Northern Ireland legislation (I have only quickyl read through it once) seems to dissapply the requirements for a risk assessment to HMOs, but not flats. Thus in blocks of flats there would still be a requirement for a risk assessment (in the common areas).
The situation where each flat owner has a share of the freehold has some interesting consequences, which I have had to deal with when working for a client who had an enforcement notice served who was in a similar situation. Normally there will still be a mangement company (formed of home owners) with a company secretary. This person would thus be the responsible person. But the impact of the legislation is that the cost of providing fire safety measures will finally rest with the owners of private homes - certainly not the intention of the legislation.
