Proposal 3 - VM2 Tall building changes

Proposal 3 - VM2 Tall building changes

This topic has been set up to capture your comments/discussion on the above proposal.

The full details of the proposed changes can be found here

You should also respond individually to the MBIE questions which can also be found at the above link.

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.

“For buildings exceeding 100m in height the loss of a sprinkler riser shall not isolate more than five floors.”

A question for the fire protection enginers and sprinkler designers, how would this work within the limitations of NZS4541, which doesn’t have the combined systems of Australia? NZS4541 also does not allow series isolation valves downstream of the alarm valve which may otherwise be required. Note that floor by floor isolation valves are required on buildings over 6 floors anyway to allow local isolation.
Pressure staging to remain within the limits of sprinkler equipment (usually 12bar) will provide a measure of redundancy depending on the design methodology ((separate risers or pressure reducing valves PRV). PRV are the most common due to cost with local stages, however there is still a single main riser.
Has a risk benefit analysis been done, as this seems to add additional complexity for little benefit, and is at odds with overseas designs in my experience.

Two risers is consistent with the IBC. The most widely used code in the USA.

Re the 10m visibility in stairs for fire fighters. My understanding is that if you have to walk up the stairs using your BA equipment on because the stair is smoke logged and also have to walk down again with the same. There is little time left to do anything useful on the fire floor.

Our team in Auckland has recently put a lot of effort into designing a tall building sprinkler system.
It required a valve set approximately every 15-20 levels to deal with pressure control.
There were two pump sets required and they designed two feed main risers to provide redundancy.

The sprinkler standard requirements differ for different parts of the country subject to Z/seismic factors.
In brief, for buildings >25m:

  • Auckland only requires a C2 ‘single superior’ water supply which has back up pumps.
  • Most of the rest of the country requires a Class A supply with two independent water supplies and pumps. Each water supply main to be taken independent to each control valve enclosure.

“For buildings exceeding 100m in height the loss of a sprinkler riser shall not isolate more than five floors”
The wording seems to suggest a valve set for every 5 levels. This is a significant cost, especially on the upper levels where floor plate areas tend to be quite small. Not only valve sets, but pressure control valves and check valves…
This sprinkler riser, after the valve set, is located in a safe stair (99% of the time) as this is where the floor zone isolate assembly has to go.
One would expect this is a ‘safe’ place to have it and with the addition of floor isolate valves, we are not sure that system size needs to be limited to 5 (potentially very small) levels.

If the intention was about the water supply feed mains, perhaps some refinement to the words…
The Class A supply or two feed main risers could meet this intention as this provides redundancy to each valve set.

Nicky Marshall
Protech Design

I have no problem with the requirement to keep the stairs clear for both occupants and fire fighters, indeed I support it. The reports from Grenfell Tower and the horrendous life and death decisions that the firefighters had to make about who to save due to the smoke logged stairs provide a graphic example.
It is more that the criteria should be the same for both, or certainly not more onerous for fire fighters than for people trying to escape. In most cases of visibility loss, it is all or nothing and if it fails 10m, it fail 5m as well or shortly after. Due to the entrainment around stair landings and the small size of stairwells, I have had models that fail 10m, but pass 5m for an extended length of time, so it can be a real design issue.
Maybe 10m is the right number for one or both groups, but it needs to be considered.

The proposed robustness check RC for buildings >60m includes failure of a town mains (and power), whcih effectively means a Class A sprinkler supply (and a generator).

A C2 sprinkler supply which requires two pump sets, at least one with a diesel engine, would cater for power failure.
Although I support the concept of Class A sprinkler supply for these buildings, it does mean considerable more costs with a water tank, more pipework and valving. It needs to be considered if the sprinkler standard is currently adequate with the C2 supply or not. What events might impair a Class C2 water supply that would not impair Class A water supply?
(Noting that this really only affects Auckland and Dunedin becuase anywhere else already requires a Class A supply due to seismic factors)

From memory the intention of this scenario was to cater for those areas which did not already require a class A supply. Also bearing in mind that CVM2 does not specify a sprinkler standard so someone could design to a standard from another country which did not have the same inherent robustness as 4541.