Meet the Speaker: Colleen Wade

Dr Colleen Wade discusses the differences between the fire behaviour of timber and traditional building materials, the danger in applying current Acceptable Solution settings to mass timber, and issues with current fire ratings.

Colleen Wade is a fire research specialist with more than 30 years’ experience. Her interests include fire modelling, flame spread, risk analysis and fire dynamics in mass timber enclosures.

At the Fire NZ Conference, Colleen will be speaking on the topics of “Fire Safety Engineering in Mass Timber Buildings - issues and solutions” (along with Prof Andy Buchanan) and “Calculating fire load and charring of timber in mass timber buildings”.

A director at Fire Research Group and a co-author of Fire Safe Use of Wood in Buildings: Global Design Guide (2022), she is also the developer of the fire zone model B-RISK. She is convenor of SC4 WG6 (design fires) in ISO Technical Committee 92 and a Fellow of SFPE.

Colleen’s PhD in Fire Engineering (University of Canterbury) focused on the modelling of post flashover fires in mass timber enclosures.

FNZM: Tell us a bit about the presentations you’ll be delivering at Fire NZ.

CW: The two presentations are closely linked. Andy [Buchanan] and I along with a whole lot of other experts around the world have been involved in writing the new book Fire Safe Use of Wood in Buildings: Global Design Guide. We’re taking the opportunity at the event to give it a bit of a profile.

The reason we helped write the book was that there is big demand for mass timber buildings due to the drive to reduce carbon emissions, etc, but there is little comprehensive guidance for their fire design given the extensive research done around the world on the topic in the past 5 years or so. There’s also a danger in applying our acceptable solutions, which were written with non-combustible structures in mind – buildings out of concrete and steel – to mass timber. The difference with mass timber is that in a fire, where panelised cross laminated timber (CLT) panels, floor plates, beams and columns are being used without protection, the timber contributes to the fuel.

Our current acceptable solution doesn’t really acknowledge this, so in the absence of any other information there’s a risk that these kinds of buildings designed according to the acceptable solution are not going to perform very well in fire. The joint paper presented by Andy and I provides a high-level overview of this, and how this new book can help.

One of the chapters in the book (Chapter 3) that I was the lead author for is about fire dynamics. It goes into some of the characteristics of fire in timber buildings and it draws out the differences between the fire behaviour in these timber buildings compared to buildings made of traditional noncombustible material.

This chapter also covers methodology for determining charring, taking into account realistic fires with a growth period, a burning period and a decay period.

It’s important to understand whether the timber elements in a compartment can withstand a burnout situation in the absence of any intervention, i.e., where the fuel runs out and the fire decays, the design should ensure that the charring also ceases. If you can do this, you can calculate what the final char depth would be after the fire and then have some confidence that you can then design the structure to carry the loads.

The problem with the current situation is that if you simply apply, for example, a 30 min fire rating from the acceptable solution, which is determined in a standard fire resistance test where the decay phase isn’t considered at all. The gas gets turned off at the end of the fire test, when the timber might still be performing structurally and as a barrier, but 10 or 30 minutes or three hours later it has continued to char and collapsed in a heap. In this case, it hasn’t really performed in terms of withstanding the structural loads and achieving fire separations that perform during and after the fire.

My presentation gives an overview of what’s in the Fire Dynamics chapter, and then the latter part of the presentation presents a methodology for working out what the char depth would be in real fire scenarios as opposed to standard furnace tests. We’re also trying to flag that we need some changes to the acceptable solutions and verification method to take these things into account.

Because there’s this strive to build taller timber buildings that we’ve never really had to worry about before, it’s important that our acceptable solutions are revised for those taller buildings. We need to be more conservative for new technology and because we don’t currently deal with mass timber very well from a fire point of view.

Building Codes around the world have traditionally been regulation by disaster. In some cases, we’ve waited until something goes wrong, and we’ve then changed the Code to fill that gap. It would be better to be proactive and not wait for that happen. If we get a bad fire, it could turn out to be a setback for all the benefits of building in timber.

FNZM: What are the drivers for building in timber?

CW: Timber is a lighter weight construction material, so for example, a timber building’s foundations don’t need to be as extensive as they might be for a concrete building. There are benefits from that point of view.

Aesthetically, architects want to build out of timber, and they generally want to display the timber rather than cover it up. This creates a bit of a conflict, because in order to prevent the progression of charring you have to protect the timber in the building. You might be able to expose some of the timber, but in many buildings you can’t expose all of it. It’s a balance, and part of the calculations the fire engineer needs to perform is around finding out how much of the timber can be safely exposed.

FNZM: One of your qualifications is from the US. Can you tell us a little about that?

CW: That was fairly early on in my career when I was with the Building Research Association, I was a fire scientist there. At that point I had a Building Science degree from Victoria University, and after a few years at BRANZ I went and did a master’s degree.

At that time – the mid-1990s – there were actually very few postgraduate programs around the world (when I went to the US the Canterbury one was in its first year). I went to study at Worcester Polytechnic Institute (WPI) in Massachusetts. They had quite a well-established program there and it was a great experience.

I then returned to my job at BRANZ and continued as a researcher especially working in the areas of compartment fire modelling and flame spread, as well as contributing to building code and standards projects.

In around 2013 I decided to do a part-time PhD at Canterbury in the mass timber area modelling fully developed fires, graduating in 2019, which got me working in the mass timber area. I left BRANZ in April 2020 and cofounded Fire Research Group with three other colleagues doing specialist fire research and advisory work.

FNZM: From the point of view of your area(s) of specialisation, what do you see as the key big issues facing fire protection?

CW: Tall timber is one and related to that the other area I have concerns about is general fire resistance requirements in tall high-rise buildings.

Our fire resistance ratings in New Zealand are very low by comparison to most other countries – sometimes three to six times lower. For example, we have 30-minute ratings for situations where other countries would have between 90 and 120 minutes and sometimes even three hours.

This may be because there’s a lack of appreciation of the risk. Most counties, for example, would have increasing fire resistance ratings as buildings get taller. They don’t have the same fire rating requirement for a two-storey building that they would for a 20-storey building because the consequences of failure of very different, but in New Zealand we treat them pretty much the same. I think there’s just a failure to match requirements with some of the potential consequences of failure. We could do better in this regard.

Another issue is the avoidance of a single point of failure. Sprinklers are obviously something you’d want to see, but sprinklers aren’t infallible. Even though their failure rates are relatively low, when the consequences of failure are very, very high as they are in a high-rise building then you’d still want to have a good balance of fire protection measures – both active and passive systems. They need to work together.

Dr Colleen Wade , Director – Fire Research Group