It is not a tali building item, however this section discusses the removal of “dependable deformation” for structural behavior in fire. While tall buildings are made from modern materials and design, if the VM is to apply to all buildings, some consideration will need to be made of buildings that do not have dependable deformation such as historic buildings with cast iron columns. This is not commonplace but could be covered by an advisory note.
For phased or staged evacuation and “defend in place” there needs to be control of smoke movement through ducts, shafts and dodgy NZ construction. Smoke dampers should be used between floors / firecells to limit the movement of smoke through the ducts, which closing a fan will not eliminate. This is the same principle as for a hospital between wards.
There is some research on smoke spread through ducts and the effectiveness of fire dampers e.g. BRE and how much smoke was transported through ducts (Examination of the fire resistance requirements for ducts and dampers, 2005). Fire dampers did not always close due to the smoke temperature, airflow and/ or the slow reaction time of intumescent dampers and a significant amount os smoke filled adjacent spaces
There is another BRE document that included fullscale testing of a room and corridor and was a result of a fatal fire in UK resthomes due to smoke spread, and I am looking in my archives for this one. There has also been other research on this topic but I would have to have a dig for it.
Smoke transport up elevator shafts is also frequently ignored and should be included in any analysis where the shaft opens onto the firecell on fire. An example is the Hester Hall dormitory fire in 1998 where 1 person died due to smoke transit through the lift shaft. There are further examples, such as the MGM Grand. It may not be such an issue in low rise buildings, however the stack effect becomes significant in tall buildings, along with the piston effect from lifts if they are used or in motion. I have been told by Opus there is no such thing as a smoke rated lift door. They all run a 6-10mm gap around them.
Question 3.15 Do you agree to the proposed changes to the C/VM2 scenario description for Design scenario (FO):Firefighting operations for tall buildings? If not, why not?
“Justification can be assisted with the Fire Brigade Intervention Model (FBIM)”.
Are the Fire Service going to release the required data for the FBIM model, and accept the results? They have always refused to do so to date. Unless this data is available, then then any reference to the FBIM model should be removed.
“ A minimum visibility of 10 m shall be provided in the stairwell from the period of Fire Service arrival, with a 100 mm wide opening in the door from the firecell of fire origin into the stairwell.”
This is a more stringent requirement than required for the occupants, who do not have BA or training or protective equipment.
What is the approach for a “blip” of smoke, such as fan speeds ramping up and down or doors opening and closing causing a local loss by the door, which may clear after a period of time ?
“ The following systems are deemed to satisfy this requirement and do not need to be demonstrated by calculation:
a) stairwell and lift pressurisation systems at 2 m/s airflow through open stair and lift doors on the firecell of fire origin.”
Is the airflow through the door with the doors open? This is not practicable as I have bene told by lift experts the lift doors will jam. They are very sensitive to pressure. Lift pressurization systems are usually based on the lift doors being closed.