Proposal 3 – Update the Verification Method VM2 - General

Proposal 3 – Update the Verification Method VM2 - General

This topic is for general discussion on VM2 changes that are not specific to a particular change.

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.

I feel that the VM2 changes focus on tall (over 60m) buildings only and ignore some very real issues elsewhere.

From the Official Information Act (OIA) information I received from MBIE, the 1000 people was based on “that was the point at which C/AS1 required sprinklers” This ignores the requirement in C/AS1 for intermediate floors to have “smoke control by specific design” and hence this basis was incorrect.
The current NZBC and C/VM2 does not require any form of smoke control for less than 1000 people, as long as FED(CO) <0.3. It is very rare to find a building that fails on this criteria, especially where it is large enough to take a lot of people at risk, which are also the buildings of greatest concern. To put this into context, it should be noted that the FED(CO)=0.3 equates to 11% of the average population being incapacitated, where FED(CO)=0.1 equates to 3% ( ). The same source notes that
an important consideration with regard to these data, particularly those related to exposure concentrations up to 50% COHb, is that they mostly relate to acute, short duration (up to around 30 min) experimental exposures of healthy young men or animals.
Applying this generally to an aging population, or in a building use that may have older or less fit and healthy occupants has significant implications to the safety of NZ buildings.
For a building with less than 1000 people, it is the same criteria for FED (CO) and visibility not being required irrespective of the use of the building, for example

  • An office, where occupants are awake and generally know the location of the exits, have fire drills and occupant density is low allowing rapid movement.
  • A sleeping group where the occupants may be slow leaving, and in the case of a hotel, they may not know where the exits are located.
  • A crowd group such as a shopping centre where parents will go to look for family members, do not know where the exits are, the exits are hard to find and the people are slower leaving than an office. In the case of a nightclub, there is also a high crowd density with the resulting injuries, and people may be intoxicated. There are plenty o international examples where this has led to a tragic outcome.
    This becomes important as visibility is not a concern so is lost early in the fire
    C/VM2 still assumes that people move at 1.2m/s through the smoke, contrary to all re research such as that of Jin in the SFPE handbook. The faster travel speed is not conservative as it reduces the CO uptake due to less exposure time.

As a result of this, there is no practical robustness check for a sprinklered building with less than 1000 people, since the acceptance criteria are the same. As a result, there are a lot of atrium buildings or those with intermediate floors under C/VM2 that do not have smoke control, as it is not required. Similarly, buildings are being designed which accept the loss of visibility in the stairs and these still “pass”, including low to medium rise single stair apartment buildings. While we expect people to have to pass through smoke near the fire in the room of fire origin, designing buildings so that people remote from the fire or in other firecells also have to pass through smoke is poor practice and contrary to international expectations.

A key point is that there is no requirements for the sprinklers to actually activate or be effective for the sprinkler allowance to apply. An atrium of say 5 stories may be sprinklered, but the sprinklers will not activate due to the cooling of the smoke plume over height. Even if the sprinklers do activate, K8 sprinklers to Ordinary Hazard or Extra Light Hazard will not be effective due to the strong plume of such a large fire dispersing the water so that it will not penetrate the fire source. It is for this reason that storage sprinklers in NZ and overseas have moved to larger and larger orifice sizes to increase the droplet sizes, and why there are different design rules, operational areas etc for pendant versus upright heads.

The premovement times in C/VM2 for sleeping groups seem fast compared with the experience in real fires. The Docklands building took 33 minutes to evacuate with the Melbourne Fire Brigade kicking people out, against the C/VM2 time of around half that. As people are relying on the short premovement time for designs that just pass, this becomes critical. There is no margin in the designs to reflect the real world.

While the proposed C/VM2 changes look at buildings over 60m, and by default require additional features, this does not apply to buildings less than 60m. In 2005 - 2006, a number of determinations were done on single stair apartment buildings, including Bankside (2005/109 as i recall), Scene and others. As part of this, I believe Tony Enright conducted a Monte Carlo risk analysis using @-Risk, which showed that additional features such as stair pressurisation were required to be an equivalent level of safety to having 2 separate stairs. The background information, sources and assumptions were meant to be released by the then DBH, but was not done so, hence we are limited to the information in the determination.

I know of at least 6 completed, current or proposed single stair apartments built under C/VM2 that have no additional features over a sprinklered single stair building greater than 25m. Furthermore, in the recent few years, some of these have been proposed to be unsprinklered.
Similarly, other than the cladding and interconnected alarm system, the Grenfell Tower building would probably get a building consent based on C/VM2, and certainly if it was shorter or sprinklered, even under the proposed changes.
If they pass C/VM2 according to the engineer and their chosen peer reviewer, they are deemed to comply with the NZBC and hence no further features are required. No consideration needs to be taken of fire service operations compromising the stair or opposing flows between fire fighters and occupants, since those requirements are deemed to comply in C/VM2 scenario FO.

Given the risk assessment in the determinations required additional features, was the risk assessment incorrect, or have we accepted a lower level of safety of these buildings, especially apartments?
It does not appear that any deliberate decision or assessment has been made on whether or not this is acceptable. Since a building which is identical to the Acceptable Solutions design under 25m can be shown to meet C/VM2 in most cases (and hence the Building Code), then it follows that the Acceptable Solutions should be extended for single stair sprinklered buildings to 59m

This ignores the poor quality of NZ buildings, especially apartments where multiple fire stopping failures can lead to a single point of failure of the escape route, smoke transport through ducts, lifts and gaps from floor to cladding or external walls (safing slots), and the experiences of buildings overseas where there have been fatalities. Larkenal house in the UK, and a fire in Ontario in 1996 (6 dead) are 2 well known cases where theory failed to match reality. Smoke transport up lift shafts and ducts is usually ignored, although if people are really going after 5 mins or less, it may not be a factor in VM2, if no reality. B- Risk is widely used even through it is not suitable for stairs. For further information, BRE have done research on fire and smoke spread through voids and ducts and fire dampers, including the effect on this on fatal fires. Su (University of Canterbury, 2001) has a good summary of fire fatalities in apartment blocks and the causes of failure.

These issues are not new, with ongoing issues going back to the Open Letter to IPENZ published by John Scarry in 2005 on slender concrete panels, the significant issues in the engineering industry raised then and also later in the Royal Commission on the Christchurch Earthquake, the ongoing Leaky Buildings scandal and the resulting huge costs, litigation and liability avoidance by all parties and the woeful construction quality and shortcuts that is widespread throughout the New Zealand building industry, such as the examples provided by Auckland Council over the last few years.
I believe we are making legally safe dangerous buildings, but as there is no obligation to do more than the building code requires under S18 of the Building Act, then no more than the minimum will be done due to commercial realities. All too often, even the minimum doesn’t get done, with deliberate shortcuts taken to save costs or meet the client’s requirements.

A good bit of analysis Geoff. Are you able to do a follow up post with some recommendations for us to think about.