Breakthrough in the understanding of flaming wildfires

I wrote a commentary article in the Proceedings of the US National Academy of Sciences (PNAS) about a recent stellar contribution to our understanding of how wildfires spread. In doing so, I have written in short the scientific context of wildland fires and also I put forward the possible impacts of the work on the field..
It can be read here ((10.1073/pnas.1512432112), and an except follows.

Breakthrough in the understanding of flaming wildfires

The rise of humanity was intimately bounded to fire. Humans first observed flames when fleeing wildland fires, the natural version of the phenomenon that would then become the most important technological achievement of the human race: the mastery of fire for cooking, lighting, settlement, hunting, and warfare (Bird 1995).
Wildfires are important to the natural sciences. Since deep time, the top surface of the Earth’s crust has been the interface where abundant plant organic matter meets an atmosphere rich in oxygen. This interface is flammable, especially in dry, windy and hot conditions, and leads to wildfire after an ignition event. Not only has fire contributed to shaping most ecosystems on Earth, but it plays essential roles supporting life through the regulation of atmospheric oxygen, the carbon cycle, and the climate (Bowmand et al. 2009, Watson et al. 1978).
As part of the current anthropogenic age, humans have also modified the fire regimes of many ecosystems, and have contributed for example to its cessation in certain regions (e.g., in the USA National Parks until 1960), or to increasing its frequency and severity through drainage (e.g., peatlands) and possibly through climate change (e.g., arctic fires). Of note, multiple US$ billions are spent annually across the world to fight wildfires for the protection of communities and valuable ecosystems.
Despite its central importance to the planet and to humanity, our understanding of fire remains very limited. For example, we currently cannot accurately forecast the location of a fire in 30 min time. To quote Hottel (1984): “A case can be made for fire being, next to the life processes, the most complex of phenomena to understand”. It comes as no surprise, then, that the discipline of fire science is less mature than other Earth science topics. For example, a quick look at the literature shows that there are three times more scientific studies published per year on volcanoes than on wildfires. Fire science requires more decades of fruitful research to mature and gain full understanding of this natural phenomenon.

Rate of Spread

The fate of a flaming wildfire starts with its genesis at ignition, by natural means like a lightning strike, or by anthropogenic means like slash-and-burn. Once ignited, part of the heat released by the flames will drive the spread over connected fuel beds of grass, shrubs, and trees. Another mechanism of propagation is by lofting burning embers that land farther away, but flame spread is more important. The dynamics of spread are such that wildfires accelerate with tail winds, dry weather, or up-slopes; and decelerate with head winds, rain or down-slopes.
The most lasting contribution to the science of wildland fires is the pioneering work of Rothermel in 1972 (Rothermel, 1972). He formulated an empirical model for predicting the spread rate of a wildfire. This formulation is ubiquitous and can be found at the core of most wildfire behaviour simulations. These simulations are currently in use by forestry agencies and firefighting command centres across the world. For example, Rothermel’s model is part of the US Wildland Fire Decision Support System, used in planning of every large and long duration federal wildland fire incident. However, Rothermel’s formulation is empirical: Whilst it can provide rough predictions of the rate of spread by calibration to previous laboratory data, it does not explain how fire spreads. Its empirical nature hinders scientific progress and does not allow for improvements to simulations. Until very recently, there was no valid scientific theory of wildfire spread that could complete Rothermel’s model.

Sketch of flame spread of a fire with tail wind over a fuel bed of fine particles. The paths for heat transfer by
radiation, convection, and flame contact are noted. According to Finney et al. (2015), the vortices are created by buoyant
instabilities and lead to ignition of the fuel by flame contact. Modified from Rothermel, 1972.

Finney et al. 2015

In this context, we see that the recent work of Finney et al. (2015) is a scientific breakthrough. Finney et al. have discovered the long-missing piece of the puzzle to understand wildfire dynamics. Their seminal work puts forward for the first time a fundamental, comprehensive and verifiable theory of flaming wildfire spread. Finney’s theory relates the rate of spread to basic fluid mechanics and heat transfer, and it is strongly supported by laboratory data and field observations across a wide range of scales from 10 cm to 15 m.

Let me put this in the framework of a simple theory. Fire dynamics dictate that spread can be seen as the succession of ignition events (Emmons 1963). This way, the rate of spread s of a fire is given in Eq. (1) by two terms, the length of fuel bed heated by the flames (expressed as δ) and the time that a fuel particle takes to ignite (expressed as tig) (Drysdale 2011).

 s=δ/tig   (Equation 1)

We know that mostly depends on flame inclination and the slope of the terrain, whereas depends mostly on fuel properties like particle size, moisture and plant composition. The scientific contributions of Finney et al. are cast around the novel identification of the two terms in Eq. 1 that govern wildfires.
First, by careful inspection of visual images of fire across scales, they show that vortex flows and peaks-and-troughs generated by the buoyancy of the flames are responsible for heating the fuel bed length δ. Then, temperature measurements then show that the intermittency of the peaks-and-troughs causes the flames to instantaneously touch the thin fuel particles, which in turn produces the contact ignition governing  tig. Figure 1 shows a sketch including these mechanisms.

Convection vs. Radiation

Their work feeds into a long-standing debate in the field on whether it is radiation or convection that controls the heat transfer to the fuel bed ahead (see Fig.1). The specific heat transfer mechanism affects the interpretation of experimental observations, and is critical in correctly formulating physically based models (Morvan 2011). Finney et al. settle the debate by identifying with strong evidence that heat transfer is controlled by flame contact, the phenomenon where both radiation and convection heat transfer are combined, but with the distinctiveness that the timing of flame contact is driven by convective flows.

Profound impact in fire science

Finney’s theory can have a profound impact in the field. The impact is four-fold regarding i) previous scientific studies, ii) wildfire simulations, iii) new technologies, and iv) multi-disciplinarity. These are explained in the following.
Previous scientific studies on wildfire spread should be revisited to help put Finney’s theory into a broader context. experimental and computational studies might need to be reinterpreted in the light of
the roles of flame intermittency and flame contact. The state of the art should naturally revisit and replace Rothermel’s model to give way to a new physically based Rothermel–Finney’s model.

Rothermel-Finney’s model would improve simulations of fire behaviour and help them gain in both accuracy and consistency. This in turn would allow the simulations to provide a more reliable layer of information during fire incidents.
The increased accuracy of simulations should eventually allow for high-fidelity forecasting technologies. A technology able to rapidly forecast the movement of a wildfire would lead to a paradigm shift in the response to emergencies, providing the Fire Service with essential information about the ongoing fire (Rios et al 2014).
The topic of wildfires is currently fragmented among the fields of biology, ecology, meteorology, chemistry, and combustion. These fields have a lot to offer one another, but better communication and cooperation are essential to move it forward. It is hoped that by strengthening the importance of fundamental knowledge and by settling long-standing debates, Finney et al. will serve as the basis for developing new multidisciplinary collaborations in the study of wildfires.

Finally, I foresee that after reading their work, many readers might start seeing the peaks-and-troughs reported by Finney et al. in every wildfire, as I already do now. As the English poet John Milton once said, “so easy it seem'd, once found, which yet unfound most would have thought impossible”.

References

• MA Finney, JD Cohen, JM Forthofer, SS McAllister, MJ Gollner, DJ Gorham, K Saito, NK Akafuah, BA Adam, JD English (2015) The role of buoyant flame dynamics in wildfire spread. Proc. Natl. Acad. Sci. USA, 10.1073/pnas.1504498112.
• MI Bird, Fire, prehistoric humanity, and the environment, Interdisciplinary Science Reviews 20(2), 141-154, 1995. DOI:10.1179/isr.1995.20.2.141A.
• DMJS Bowman, JK Balch, P Artaxo, WJ Bond, JM Carlson, MA Cochrane, CM D’Antonio, RS DeFries, JC Doyle, SP Harrison, FH Johnston, JE Keeley, MA Krawchuk, CA Kull, JB Marston, MA Moritz, IC Prentice, CI Roos, AC Scott, TW Swetnam, GR van der Werf, SJ Pyne, Science 324 (5926), 481-484, 2009. DOI:10.1126/science.1163886. 
• JE Watson, Lovelock, L Margulis, Methanogenesis, fires and the regulation of atmospheric oxygen, Biosystems 10 (4),pp 293-298,1978. 
• HC Hottel, Stimulation of fire research in the United States after 1940, Combustion Science and Technology 39:1–10, 1984. doi:10.1080/00102208408923781.
• RC Rothermel, A mathematical model for predicting fire spread in wildland fuels, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah, Research Paper INT-115, 1972. 
• HW Emmons, Fire in the forest, Fire Research Abstracts and Reviews 5, 163, 1963. 
• D Drysdale, An introduction to fire dynamics, 3rd edition. John Wiley and Sons Ltd, Chichester, 2012. 
• D Morvan, Physical Phenomena and Length Scales Governing the Behaviour of Wildfires: A Case for Physical Modelling, Fire Technology 47 (2), pp 437-460, 2011. doi:10.1007/s10694-010-0160-2. 
• O Rios, W Jahn, G Rein, Forecasting wind-driven wildfires using an inverse modelling approach, Natural Hazards and Earth System Sciences 14, pp. 1491-1503, 2014. doi:10.5194/nhess-14-1491-2014

Improved travelling fires for structural design

The collapse of 1WTC, New York City, 10:28am Sept 11, 2001.
Photo by 9/11 Photos CC BY.

Our latest paper on travelling fires for structural design has been published in Structures (journal of IStrutE) with the title Improved formulation of travelling fires and application to concrete and steel structures.

Note: It is open access so you can read and share it without need for a subscription. We have posted in open access also our Matlab code to calculate the fire temperatures in zenodo.


Accidental fire can be disastrous, especially in buildings. The effect of fire on structural stability is critical in regard to safe evacuation and safe access for fire fighters, financial losses, and lost business. This is particularly the case in tall buildings where extended evacuation times are required due to phased evacuation practices. The World Trade Centre Tower fires in 2001 have highlighted the need of a more realistic design tools to represent fires in large compartments. 

Innovative architectural designs of modern buildings already provide a challenge to structural engineers. This is above all the case in structural fire engineering. However, most of the understanding and current design codes are based on the assumption of uniform fires in a compartment. In previous work, we have shown that fires in large, open-plan compartments, typical of modern architecture, travel from one part of it to another with non-uniform temperature distribution. These fires are referred to as travelling fires. And Travelling Fires Methodology (TFM) has been developed to account for the travelling nature of fires.

Illustration of a travelling fire and distribution of gas temperatures.

TFM was born in 2010 and offers a paradigm shift in the structural engineering of modern buildings. The concept has already been applied by engineering firms like Arup, BuroHappold or AECOM in the design of a dozen of iconic buildings in the UK (including the renovation of Battersea Power Station in London). TFM accounts for one of the fastest knowledge transfers from research to industry seen in fire protection engineering. TMF is now being studying in detailed in the USA for possible adoption as well.

The focus of this latest paper is on the improvement of the calculations of traveling fire (iTFM) to account for better fire dynamics, and the analysis of the effect on structural members. The proposed changes represent a simple yet powerful fire model. In particular, our paper shows that:

• Using data from experiments and real fires, we limit the range of possible fire sizes thus reducing the time required for conduct TFM studies.
• Analytical expressions are presented for generating time–temperature curves which are independent of grid size (previous versions of TFM) and can be easily calculated with any mathematical tool. 
• Introduction of flapping term leads to reduced near-field temperatures for smaller fire sizes which cover a range between 800 and 1200 °C, as observed in real building fires. 
• The location of the peak temperature in the compartment is found to occur at the end of the fire path (i.e. far half of the compartment from the ignition source).

9/11 World Trade Center Attacks: Engineering Lessons After the Collapse of the Towers

I recently wrote an editorial on the 2001 World Trade Center attacks to introduce an incoming special issue in Fire Technology. It has now been published and can be read here (open access). I reproduce below an excerpt from it.

9/11 World Trade Center Attacks: Lessons in Fire Safety Engineering After the Collapse of the Towers

September, by Gerhard Richter 2005, at MoMA.

"Every engineering discipline has been shaken by tragic events at some point. Ralph W. Emerson (1803–1882) wrote that “We learn geology the morning after the earthquake”. Humans tend to identify gaps of knowledge after a catastrophe. Over time, progress and modern societies have established the means to set up major independent investigations after a technological disaster strikes. Their objective is to unearth the causes and learn lessons from the event so that similar catastrophes are avoided in future. In order for this to happen, it is essential that the results of the investigations are widely disseminated and that the scientific community carefully analyses them, critically assesses them and further improves the conclusions and lessons. This special issue invites the fire safety engineering community to just do that with respect to the 9/11 attacks on the World Trade Center (WTC) in New York.

WTC towers 1, 2, 5 and 7 collapsed because of the fires triggered by the attacks. From causes to consequences, this disaster touched on a wide range of scientific disciplines. Understanding it thus requires a multidisciplinary approach, and its most important elements are covered in this special issue".

[...]

"This is perhaps best illustrated by an example. In September 2011, 10 years after the attacks, the international magazine Scientific American published an article (“Castles in the Air”) on the WTC disaster’s effect on the design of new tall buildings. It concluded that high rise buildings needed to be kept away from aircrafts and should have means for prompt evacuation; it did not discuss protection from fire. However, WTC 1, 2, 5 and 7 collapsed because of the fires the attacks had triggered—they had resisted the aircraft impacts (WTC 5 and 7 were not even hit) and most of the occupants below the floors of impact were able to safely evacuate".

[...]

--

The full reference is: 

G Rein, 9/11 World Trade Center Attacks: Lessons in Fire Safety Engineering After the Collapse of the Towers, Fire Technology 2013 (in press). http://dx.doi.org/10.1007/s10694-013-0337-6

Fire protection and polymers: natural flame retardancy

While investigating the limitations of the theory that explains the ignition behavior of a polymer, we discovered something unexpected, a new natural flame retardancy mechanism.

In the UK, a fire is started every 3 min, and over the course of a year, the cost of fire totals approximately £7 billion [1]. It is a major threat, and continues to be the leading cause of property damage worldwide according to the insurance company FM Global. In the modern world, polymer materials are ubiquitous because of its technological, manufacturing and commercial advantages. But they also fuel flames, and are a prime actor in accidental fires. Better understanding of how polymers burn is a necessity if we are to save human lives, protect infrastructure and the environment, and improve businesses.

Ignition is a key process in the initiation and growth of fires. The risk of fire is associated to the ease of igniting the materials present. This is true for the initiating event but also for the subsequent spread. For example, the flames and the hot smoke transfer heat to nearby fuels, igniting these too, thus leading to further growth of the fire.

Pyrolysis is the thermochemical process by which a solid (or liquid) decomposes and produces the gaseous fuels that feed a flame. When a solid fuel is heated it eventually reaches a temperature threshold where it begins to break down chemically (typically around 200 to 300 C). Pyrolysis is similar to gasification but with two key differences, i) pyrolysis is the simultaneous change of chemical composition (e.g. long hydrocarbon chains to shorter chains) and physical phase (i.e. solid or liquid to vapour); and ii) is irreversible. It is an endothermic reaction, meaning that it needs an external supply of heat to continue because the products carry more chemical energy than the original fuel. It does not involve oxidation reactions.

Watch this accelerated video to see the pyrolysis of a block of PMMA, a synthetic polymer used in plexiglass, when it is exposed to a strong source of radiant heat (arriving from the top).

Since World War II, laboratory experiments performed with radiation heat sources have provided a basic understanding of ignition. It has led to what is called the classical ignition theory. This theory allows to calculate the time it takes to ignite a solid fuel when it is exposed to heat. It was developed from experiments conducted at low levels of heat (in the range below ~70 kW/m2). The theory says that the time to ignition decreases with the square root of the incident heat. These calculations have been used extensively in fire science and in fire protection engineering for decades. Although the expression has been altered slightly many times as research developed, it has kept pretty much the same mathematical form (=inverse square root for all heat flux levels).

But in 2006, researches at Worcester Polytechnic Institute conducted experiments at high heat fluxes, up to 200 kW/m2 on a range of polymers (PMMA and wood, for example). Their experimental data could not be predicted correctly by the classical theory. The error at high heat levels was large. Instead of the expected continuous square root behavior, the measurements were diverging from theory with a gradual flattening towards a constant ignition time for heat levels above ~80 kW/m2. The researchers could not explain the phenomena but reported their measurements [2]. This data posed a challenge to the scientific community.

This is an important failure because in large accidental fires, most of the radiative heat arriving to nearby fuel items is above 100 kW/m2. Thus, if this error is not corrected, predictions of the pattern and the rate of spread of a fire will be erroneous. Also, this failure of the ignition theory marks a limitation of our understanding and hinders the development of new fire protection technologies.

Measurements of the time to ignition of PMMA samples found in the scientific literature. The cloud represents experimental uncertainty. Top: Inverse of the square root of the delay time to ignition vs. heat flux (inset: zoom for heat fluxes up to 60 kW/m2); Bottom: Delay time to ignition vs. heat flux. Figure from [3].

So, in 2008 we picked up the challenge and tried to solve this riddle. We conducted a detailed investigation [3] of all the experimental data in the literature for the polymer best studied in fire science: PMMA. Data extended from low to high heat levels, see figure above. We then used a comprehensive numerical model of pyrolysis to revise all the assumptions cast in the classical ignition theory. We interrogated the experimental data using the numerical model to tell us why the failure. We wanted to identify the assumption and the mechanism (or mechanisms) responsible for the unexpected failure at high heat levels. All possible physical and chemical assumptions were systematically studied, one-by-one and combining them. We found it at the end. The classical ignition theory makes a wrong assumption and misses an important mechanism, a physical one, related to radiation heat transfer (and related to optics as well).

The problem is that the classical ignition theory assumes that the radiation is absorbed at the exposed surface of the material. We found that this is a good approximation to all materials at low heat levels, but it is not a valid assumption for many materials at high heat levels [3]. The assumption breaks down at high heat, with PMMA for example, because this material is translucent to some radiation. We could correct the ignition theory by taking into account that a fraction of the radiation penetrates directly in-depth, into the material, such that the surface heats up less. This leads to slower ignition and slower fires. The elusive mechanism is called in-depth radiation absorption.

This discovery was also reached simultaneously and independently by researchers at FM Global [4], although using an analytical approach and a smaller experimental data set. We learn about FM Global's work after presenting our findings at an international conference (BCC 2009 Recent Advances in Flame Retardancy of Polymeric Materials), so we were lucky to be able to cite them too and include their data in our final version published in 2010 [3].

The discovery is important because many polymers are known to exhibit some degree of transparency to radiation. PMMA is just one example, the example for which most fire data exists. Due to in-depth absorption, a material delays ignition because heat reaches directly deep into it thus leading to lower temperatures at the surface and hence taking longer to reach ignition. The work shows that in-depth radiative abortion acts as a natural fire retardant in polymers; it helps to 'cool down' the surface when heated.

This mechanism could be exploited by the plastic industry to design new polymer formulations that favor materials that are transparent to radiant heat and absorb less at the surface but more in-depth. It might help to formulate physical flame retardancy, whereas currently the plastic industry relies mostly on chemical retardants.


References:

[1] An Introduction to Fire Dynamics, 3rd Edition, 2011, by Dougal Drysdal, Wiley. 

[2] Flammability characteristics at applied heat flux levels up to 200 kW/m2, by P Beaulieu and N Dembsey in  Fire and Materials, 32(2), pp. 61-86, 2007

[3] Numerical Investigation of the Ignition Delay Time of a Translucent Solid at High Radiant Heat Fluxes  by N Bal and G Rein in  Combustion and Flame 158, pp. 1109-1116, 2011.

[4] Absorption of thermal energy in PMMA by in-depth radiation by Jiang, De Ris and M.M. Khan, Fire Safety  Journal, 44 (1), pp. 106–112, 2009

Travelling fires paper wins Lloyd's Science of Risk Prize

Feb 2013 update: Read more about this work and how it ended up in a real building in this post.

We have won the 2011 Lloyd’s Science of Risk Prize in the Technology category for the paper "The Influence of Travelling Fires on a Concrete Frame" (published in Engineering Structures 33).

Winners of the 2011 Lloyd’s Science of Risk Prize. Dr Law is is second from the right.

The work argues that the trend towards open plan offices has changed the types of fire likely to occur in modern buildings. His paper uses science to look at ways to improve engineering guidelines and building design, reduce the risk of travelling fires, and help insurers better quantify and model fire risk. The work was founded by BRE Trust and Arup.

 Progression of the 2.5% and the 25% travelling fires across the floor plate (Fig 4 in the paper)

Temperature profiles for the average rebar in the final bay (Fig. 8. in the paper)

The Science of Risk Prize was launched by Lloyd’s in 2010 to stimulate cutting edge research into the latest emerging risks facing businesses.

For more details on the work, see here the paper (open access), a poster and related presentation.


NOTE: My team also won the 2010 Lloyd’s Science of Risk Prize in the same category with a paper on the modelling of tunnel fires. Two in a row :)

Modelling of transient flows in tunnel fires

Our most recent paper on tunnel fires has just been published in the journal Computers and Fluids. The title is:

Multiscale Modelling of the Transient Flows from Fire and Ventilation in Long Tunnels

The paper applies a transient multiscale approach to model ventilation flows and fires in a long tunnel. It couples dynamically a Computational Fluid Dynamics solver with a simple 1D model, allowing for a more rational use of the computational resources without loss of accuracy.

Schematic of the multiscale model of the1.2 km tunnel from portal to portal and including 10 jet fans pairs. The CFD domain of the fire region contains temperature contours showing the fire plume.

After all the fundamentals of the coupling are discussed, the methodology is applied to study the unsteady flow interaction between a growing fire and a ramping-up ventilation system in a modern tunnel (7 m diameter, 1.2 km long). To the best of our knowledge, this is the first time than a growing fire and a growing ventilation are studied together. The results allow for simultaneous optimization of the ventilation and detection systems, and allows engineering answers to questions that could not be posed before by tunnel designers.

Longitudinal velocity field computed 180 s after fire ignition (60 s after ventilation activation) for three ventilation scenarios (3, 5 or 10 jet fan pairs respectively). Velocity values are expressed in m/s.

The work is a continuation of the collaboration between Politecnico di Torino and University of Edinburgh led by Dr Francesco Colella (the work is based on this 2010 thesis "Multiscale modelling of tunnel ventilation flows and fires").

NOTE: An earlier paper related to this received the 2010 Lloyd's Science of Risk Prize.

Laser guns and Ignition times - research paper

We have published recently a paper in Combustion and Flame titled "Numerical Investigation of the Ignition Delay Time of a Translucent Solid at High Radiant Heat Fluxes"

This investigation revisits the theory explaining the ignition of a solid surface via a radiation external source. It led to a discovery affecting our understanding of how fires start and spread. The paper explains the failure of the classical ignition theory in polymers by using all the experimental data available to date and using a computer model to identify the missing mechanism causing the classical theory of ignition to fail when heat flux level are high. This mechanism is in-depth radiation, aka, the fact that many polymer materials are translucent to radiation.


This finding could help the US Navy fine tune their latest gadget. The BBC reports that they have fired a laser gun from one of its ships for the first time. They used a high-energy laser to carefully deliver a high flux of energy to the polymer surface covering the boat engines. This created a hot spot that reached ignition after some time, setting the engines on fire and disabling a boat. The ignition time can range from a few seconds to minutes, depending on the power of the laser. See the figure below extracted from the paper.

Time to ignition of black PMMA samples for a wide range of experimental conditions in the literature.

Our paper, and the model used in it, allows to calculate with higher precision the time required to reach ignition depending on the power of the laser and the material being heated. Higher precision calculating  the ignition time avoids failed attempts and reduces expensive laser time. It would lead to a more reliable and less costly weapon. The better tuned damage caused would be useful in non-lethal applications as well.

More at: N Bal and G Rein, Numerical Investigation of the Ignition Delay Time of a Translucent Solid at High Radiant Heat Fluxes, Combustion and Flame 158, pp. 1109–1116, 2011 http://dx.doi.org/10.1016/j.combustflame.2010.10.014

Forecasting Fire Growth

We published recently a paper in Fire Safety Journal titled "Forecasting Fire Growth using an Inverse Zone Modelling Approach". We are happy that the work has been widely featured in the media and many people is being exposed to the novel idea:

• Interview for Scottish TV News (aired on 29 Nov 2010)
• Interview for BBC Radio Scotland (aired on 29 Nov 2010)
• Articles in The Scotsman, CORDIS-EU and Xinhuanet (in Chinese).

The idea is based on the fact that effective control of a compartment fire saves lives and money. When fire fighters manage to put out a fire before it grows out of proportions, live safety is greatly increased and significant damage can be avoided. Moreover, the affected building can be re-occupied without major investment of resources. But when a fire passes a certain size, the building might collapses as a consequence of the fire damage to the structure (eg, 2001 WTC or 2005 Windsor Tower) or might have to be demolished due to irreversible damages.

Due to a lack of the required technology to support emergency response, fire fighters often have to follow their intuition when it comes to attacking the fire instead of basing their decisions on knowledge of the actual fire. This lack of information can lead to lost opportunities or unnecessary risks.

Prediction of the ongoing fire development ahead of time under different possible conditions based on the current events taking place would give fire fighters insight into the dynamics of the particular fire being flighted. With this extra knowledge, they could weight other options and feed more information into the emergency management. However, fire dynamics follow complex physical processes closely coupled to one another, which makes current tools not able to accurately forecast fire development in real time.

This emerging technology has been called Sensor Assisted Fire Fighting. The FireGrid project, to which this paper belongs together with the recent PhD thesis of the lead author, aims at providing physics-based forecasts of fire development by combining measurements from sensors in the fire compartment with a range of computational modelling tools. The sensor measurements can provide essential lacking information and compensate the accuracy lost, and thus overcome the shortcomings of current modelling tools and speed them up. The proposed methodology is to collect measurements in the fire compartment, and to assimilate this data into the computational model.

When enough measurements are available to characterize the current fire, a forecast is made. This forecast is then constantly updated with new incoming data. If, for example, a door is opened or glazing breaks, and the ventilation conditions change drastically, the sensor measurements will steer the computational model towards capturing the new conditions. With this technology, fire fighters could act upon forecast behaviour.

This paper presents one of the first steps in this direction. Data is assimilated into a simple zone model, and forecasts of the fire development are made. Positive lead times are reported here for the first time. These results are an important step towards the forecast of fire dynamics to assist the emergency response. Together with the application to CFD within the same PhD thesis, the previous thesis of Cowlard on flame spread predictions and the most recent paper by Koo et al. on probabilistic zone models, these establish the basis for technology for sensor assisted fire fighting. The envisioned system is not yet fit for operational purposes and further research is needed. The investigation of the effects of adding further realism in the fire scenarios will be the focus of future studies.

NOTE: This paper was short-listed within the top 5 submissions to the Lloyd's Science of Risk Prize in the Technology Category. See related article Hot talent in risk research in the Staff Bulletin of the University of Edinburgh.