Hi Paul
Yes its sometimes very difficult to have to break such bad news to people who have genuinely tried over the the years to do everything required of them and have been the victims of poor service and bad advice.
Couple of observations and please forgive me if I am going over old ground.
During the early years of the care homes boom in the early 80s many old buildings were converted, many of which had decorative lath and plaster ceilings - and the draft guide was looking for an hours fire resistance between floors. A number of proprietary methods were devised to improve the fire resistance from above subject to appropriate specifications. Two that I recall involved lifting some floorboards in the room above, nailing chicken wire between the joists and infilling between the joists with mineral fibre or Tilcon made a lightweight cement product.
As far as lath and plaster is concerned the thickness of the plaster and its condition are paramount to its fire resistance. If I recall tests for English Heritage concluded that if there was a covering of at least 12.5mm over the laths, if this was consistent and free from cracks and damage then it may have a nominal half hour standard. I have had a look at a lot of ceilings and a consistent plaster thickness of 12.5mm is very rare in my experience- usually areas are much thinner than this.
As far as walls are concerned then fire resistance properties are unpredictable and through the laths can be ignited through conducted heat from a not too significant fire in the room- this leads to very rapid uncontrolled fire spread. I learned this the hard way on a recall to a fire many years ago but thats another story.
So I guess if you do have this problem and if the ceilings have not been upgraded invisibly (Heres hoping) I would suggest a 5 year plan - review and identify the most critical areas of the building and incorporate a range of solutions, focussing on critical areas to life safety and using a variety of techniques as appropriate to the circumstances.
