The initial problem as I see it is the main thrust of the fire safety legislation and risk assessment is that the fire exits do not become blocked and the fire engineering goes to some pains to ensure that the exits remain available. If there are going to be problems with the exits becoming blocked this is going to be due to malicious human activity i.e. terrorism or arson.
However there is one problem I have come across, the scenario is you have a multi storey building which is owned by a housing association there is a tenant on an upper floor who has been there for a long time who, when they first moved in could get themselves out quite easily, but now have difficulty due to their age etc. The tenant does not want to move to another flat and the housing association does not want to force the tenant to move. The problem get that person out, without assistance, the apparatus has to be retrofitted and must not be to costly,