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Wednesday, August 26, 2009

Visit by Dr Jomaas and seminar on Spherical Flames

Dr Grunde Jomaas, Lecturer in Fire Safety at Technical University of Denmark (DTU), is visiting the fire group and will give a seminar on Wed 2 Sept at 1pm in the Alexander Graham Bell Bldg. seminar room (3rd floor).

Dr Jomaas is a 2008 PhD graduate from Princeton University. In 2001, he got a BSc in Fire Protection Engineering from the University of Maryland (where he worked with Prof Jose Torero). After a year of research at Ecole Centrale Paris, he move to DTU Denmark in 2009. On top of his academic position, he is active in consultancy as a fire safety and combustion expert.

Seminar Abstract:
Experimental Observations of Propagation and Stability of Spherical Flames

High-fidelity experiments were conducted to define the transition boundaries of both cellular and spiral flame front instabilities, and also to determine cellular flame acceleration constants for outwardly propagating spherical flames in a dual-chamber design that allows near-constant experimental pressures up to 60 atmospheres. The flamefront movement was monitored using schlieren cinematography and recorded with a high-speed digital camera. The instant of transition to cellularity was experimentally determined for various fuels and fuel mixtures and subsequently interpreted on the basis of hydrodynamic and diffusional-thermal instabilities. Furthermore, exciting observations of spiral waves and target patterns over propagating flame surfaces in rich hydrogen-air, rich hydrogen-oxygen, and lean butane-oxygen-helium mixtures are shown to be well described by the Sivashinsky criterion for instability.

* See 2007 paper on Journal of Fluid Mechanics, "On transition to cellularity in expanding spherical flames".

Thursday, August 20, 2009

Blind vs Open fire modelling

I always wanted to start a debate on this topic and now think that a better way is using the blog.

Three years after The Dalmarnock Fire Tests, the 'a priori' vs. 'a posteriori' debate in is still not too popular in the fire modelling community. The debate seems to be mostly taking place in personal communications and during the peer reviewing of papers. Unfortunately, not much is happening publicly or at the reach of the fire community as a whole.

Figure 1: Dalmarnock Fire Test One as seen from the outside, 18.5 min into the fire. (from [ Abecassis-Empis et al, Experimental Thermal and Fluid Science 2008]).

The problem is the following (summary). When making comparisons of modelling results to experimental measurements, there are two general approaches that can be followed: a priori (aka blind) and a posteriori (aka open). In a priori simulations, the modeller knows only a description of the initial scenario. The modeller has no access to the experimental measurements of the event and thus will be providing a true forecast of the quantities of interest. In a posteriori simulations, before the simulation is run the modeller knows the initial scenario and also how the fire developed (ie via the experimental measurements). Most fire model validations in fire engineering has been conducted a posteriori.

Only comparison of a priori and a posteriori simulations of the same event allows to investigate the possible effect that maybe has been introduced by prior knowledge of how the event developed. The importance of this effect in fire safety engineering is currently an advanced research topic and under study by different research groups.

The 2006 Dalmarnock Fire Tests conducted in a high-rise building were used to look into the problem. An international study of fire modelling was conducted prior to Dalmarnock Fire Test One. The philosophy behind the tests was to provide measurements in a realistic fire scenario with very high instrumentation density (more than 450 sensors were installed in a 3.50 by 4.75 2.45 m compartment). Each of the seven participating teams independently simulated the test scenario a priori using a common detailed description. Comparison of the modelling results shows a large scatter and considerable disparity among the predictions and between predictions and experimental measurements. These results tend to shock, please and anger the audience in equal parts. See Figure 2 below.

Figure 2: Evolution of the global heat release rate within the compartment. Comparison of predictions and experimental measurements. (from [Rein et al, Fire Safety Journal 2009]).

An exception to the relative silence of the fire community are the two magazine articles of Dr Alan Beard from Heriot-Watt University. These can be accessed here:

First note that I disagree with blanket statements like "a predicted result from a model cannot be assumed to be accurate; ie to reflect the real world". Our work also shows that fire simulations provides fire features that may be good enough to be applied towards engineering problems if a robust and conservative methodology is defined. A prerequisite for this methodology is that it can use predictions with crude levels of accuracy and that it applies appropriate safety factors. But Dr Beard has an important point in that 'real world' fire engineering applications are most frequently applied to simulate events which real behaviour had not been (and will never be) measured. These simulations are a priori simulation, not a posteriori. However, most fire model validations in fire engineering has been conducted a posteriori. I certainly agree with Dr Beard on this one; we need more a priori comparisons of fire modelling and address full model validation. What is the effect of prior knowledge of the fire development? Would the validations provide the same conclusions if conducted a priori? The problem is not unique to fire engineering and any discipline dealing with complex simulations tools should be facing this question. I do not know how other disciplines cope with it.

The differences between a priori and a posteriori modelling become patent when comparing the round-robin results with the work conducted after the Dalmarnock data was publicly disseminated. Subsequent studies (Jahn et al. 2007, Jahn et al. 2008 and Lazaro et al. 2008) show that it is possible to conduct a posteriori fire simulations that reproduce the general fire behaviour to a satisfactory level. This was achieved due to the availability experimental data of the real behaviour for reference, allowing for iterations until an adequate input file was found.

I would like to finish with the same final words I use when presenting the results in conferences and seminars. We, the authors of the Dalmarnock round-robin, are professionals of, and supporters of, fire modelling. We want fire modelling to improve and be developed further. Our daily work goes in that direction.

I am interested in hearing your comments.
.Guillermo Rein.

NOTE #1: All the relevant information, book and papers about The Dalmarnock Fire Tests are accessible in open access here.

NOTE #2: There are two points about Dalmarnock that need to be emphasised since are often misunderstood. These are:
  • The aim of our a priori work was to forecast the test results as accurately as possible, and not to conduct an engineering design with adequate conservative assumptions or safety factors.
  • Experimental variability was one of our greatest concerns and that is why the scenario was designed for maximum test reproducibility. The Dalmarnock Fire Test One was benchmarked against a second test to establish the potential experimental variability. Results show that the scatter of the a priori simulations is much larger than the experimental error and the experimental variability together.

NOTE#3: No matter how useful and interesting the results from blind simulations are, only three blind round-robins on fire modelling can be found in the historical records of the discipline. The other two are the 1999 CIB and the 2008 French PROMESIS project. All three round-robins overwhelming agree on the results, but the Dalmarnock one was the first to be publicly communicated and the one providing, by far, the largest instrumentation density.

NOTE #4: I initiated a related discussion on this topic in April 2008 in the FDS forum. See here.

Monday, August 17, 2009

Important accidental fires covered by the media - updated

This is a list updated once in a while with the most interesting fire accidents and events in the media.

PD: Special thanks to Cecilia and Adam for providing most of the information here.

* Oct 2009 - Peat fire burning since September in the Spanish National Park Las Tablas de Daimiel in Castilla la Mancha is caused by prologued drought and clearly shows the pipe system feeding air to the subsurface fire. In Oct it was affecting 5 ha of land. The Guardian. El Pais (in Spanish), El Pais 2(in Spanish) (video).

* August 2009 - Peat fires in Indonesia have now become perennial during dry seasons Jakarta Post. See here satellite imagines of Borneo on September 15, 2009. Special report on The Economist.

* August 2009 - Los Angeles Fires out of control NYT. A wildfire raging in the mountains north of Los Angeles spread consuming thousands of acres of national forest land and threatening at least 10,000 homes. The fire was blamed in the deaths of two firefighters who were retreating from flames that overran a camp.

* August 2009 - Greek fires roar with gale force winds. BBC News(video) timesonline. About fifteen thousand residents of Athens's northern suburbs were forced to leave their homes as large areas of forest were burnt. Some residents have refused to leave, choosing to fight the fires with whatever they can lay their hands on. Nearly 2,000 firefighters and soldiers are engaging the blaze on the ground, together with hundreds of volunteers.

* August 2009 - Blame it on turbulent eddies. Timesonline (video). The attempt to break a world record by igniting 114,000 fireworks in less than a minute ended up in a 6.5s explosion witnessed by 200,000 people who lined the seafront in Bournemouth, UK. The managing director blame on the weather forecast.

* August 2009 - Report of Australia's worst peacetime disaster has called for a radical overhaul of the bushfire warning system. BBC News

* August 2009 - Fire chiefs support "fire safe" cigarettes in Scotland. BBC News. Some 44.8% of fire deaths in Scotland in 2007/08 were attributed to the smoking problem. The state of Vermont in the US introduced legislation in 2005 to ensure that all cigarettes were fire safe - and subsequently recorded no fire deaths attributed to cigarettes in 2007 and 2008.

* August 2009 - 4,000 people evacuated in Canary islands. Timesonline. Some 250 firefighters, two helicopters and five planes are involved in tackling a forest fire in island of La Palma, the cause of which is unknown.

* July 2009 - Fire claims four lives in Spain. BBC News(video) CNN. Four firefighters in Spain have been killed while trying to tackle a blaze at a nature reserve in the north-east of the country. Two firefighters also suffered injuries in the incident, the worst to occur since 11 firefighters died nearby in 2005. The fire in Horta de Sant Joan in Tarragona province had been under control but winds revived it, trapping the four firefighters. Some 8,000 hectares (nearly 20,000 acres) have already burned in Aragon, forcing the evacuation of more than 1,600 people. More than 800 Spanish troops are also fighting numerous forest fires across Spain.

* July 2009 - Firefighter dies in Edinburgh pub blaze as floor collapses. BBC News(video)

* July 2009 - Indonesia may experience more severe peat fires this year because of an extended dry season raising the prospect of choking smoke blowing across neighbouring states. Reuters.

* July 2009 - Dozens of fire-fighters battled a massive blaze at a club in Edinburgh BBC News

* July 2009 - 17,000 residents flee wildfires in Canada. BBC News(video). Wildfires near a western Canadian city have forced the evacuation of around 17,000 people. More than 150 firefighters are tackling the blazes in British Columbia, with support from 10 helicopters and eight water bomber planes.

* July 2009 - Blaze in Soho, London. BBC News (video) Timesonline (video). A fire at a four-storey office building in Dean Street, Soho, in the historic area of London. 60 firefighters and 12 fire engines attended the fire which witnesses said started in an air conditioning duct in the building.

* July 2009 - Hundreds flee as military drill sparks bushfire in Marseille. Timesonline(video).

* July 2009 - London: Three children and three adults have died after a fire swept through a tower block. BBC News and BBC News

* July 2009 - Accounts of "volcano of fire" around the town of Mojacar in Spain. BBC News(video).

* July 2009 - The derailment of a freight train carrying liquid gas triggered a
massive explosion killing at least 14 people. timesonline(video).

* July 2009 - Aircraft burst into flames on landing at an airport in northern Iran, killing at least 17 passengers. BBC News(video).

*June 2009 - Four escape firebombed restaurant: three bottles of accelerant were thrown through the window. BBC News

*June 2009 - Mexican nursery fire kills many
BBC News. At least 38 children have been killed in a fire that swept through a state-run day-care centre in north-western Mexico, city of Hermosillo. The fire appears to have started in a tyre depot.

*June 2009 Man sentenced to death penalty for 2006 California wildfires BBC News. A court has sentenced a man to death for the first-degree murder of five firefighters by starting an October 2006 forest blaze.

*June 2009 Bus fire kills 25 in Chinese city
BBC News (video). At least 25 people have been killed and 78 wounded in a bus fire in central China, state media reports.

*May 2009 Building fire in frost Antarctica
BBC News. An isolated hut in Antarctica favoured by explorer Sir Edmund Hillary has burnt down after a fuel leak during a routine inspection at minus 35C.

*May 2009 Firefighters tackle blaze in Edinburgh. BBC News. Dozens of firefighters have been tackling a major blaze in the Dalry area of Edinburgh. When the Lothian and Borders firefighters arrived, they found a two-storey warehouse well alight.

*May 2009 Fire in the headquarters of the European Commission in Brussels. BBC News(video). Timesonline. "Journalists working in the press room, known as "the bunker", said they had noticed a steady build-up of smoke for 20 minutes before then, but that the smoke detectors had failed to react." There's a "human behaviour in fire" observation. They were aware of smoke for 20 minutes but because nobody raised the alarm, they didn't leave the building! Would the EU increase funding in fire safety now?

*May 2009 Blaze breaks out at Fire Service College in Gloucestershire BBC News(video). "Twelve fire engines are stored in the building at the college in Moreton-in-Marsh along with 1,200 litres of diesel and 500 litres of hydraulic oil. Eleven of the fire engines have been destroyed at a cost of £116,000 each"

*May 2009 Gas Pipe Fire in Russia, 100 m high flames. BBC News(video)
BBC News
(video). "A gas pipeline has exploded in Moscow sending flames 100 metres into the air and setting fire to a nearby building. The Russian authorities have shut off the gas supply to the area and are investigating the cause of the blast"

*May 2009 Californians flee deadly wildfire
BBC News(video). "Thousands of people in California have left their homes as a wildfire threatens the town of Santa Barbara. The rapidly-moving blaze has burned nearly 3,000 acres, leading California Governor Arnold Schwarzenegger to declare a state of emergency. "

*May 2009 Gaming hall fire in Ukraine
BBC News(video). "10 people have been killed after a fire swept through a gaming hall in eastern Ukraine"

*April 2009 Commuter train on fire
BBC News. "A commuter train had to be evacuated during the morning rush hour after smoke was spotted coming from underneath the train."

*April 2009 Fire in the Coca-Cola building, London BBC News(video)
The Telegraph. "A fire that broke out in building in Hammersmith, west London, has disrupted bus and Tube services. A fire brigade spokesman said the blaze began in an electrical sub-station on the 6th floor of the Coca Cola building in Queen Caroline Street".

Sunday, August 16, 2009

Prof Howard Emmons applied the first fire model in 1980

I just found this interesting old TV show where Howard Emmons speaks of the 1980 MGM Las Vegas fire and of the fire code Harvard. Howard Emmons, Professor of Mechanical Engineering at Harvard University was one of the fathers of modern fire science. In this fire investigation, Prof. Emmons used a computer fire simulation to study a real fire for the first time in history.

-Go to min 1.52 into the video to watch the interview with Prof. Emmons.
-Go to min 6.40 and 8.00 to watch the fire code Harvard.
-Go to min 7.18 to watch David Lucht and Cone Calorimeter experiments conducted at WPI.

I never met Prof. Emmons, so I really appreciate the opportunity to hear and watch him talk about fire science and fire modelling.

Monday, August 10, 2009

A day off from studies at the Highland Games in North Berwick

by Anna M Jonsdottir, 2009 MSc student in Structural and Fire Safety Engineering.

When there are 10 days until your deadline for the MS.c dissertation what is better than taking the day off to go and breath in the local culture? Well maybe it would have been more logical to sit at home and work, work, work but since my brain was on the verge of overflow or short circuit, the day off was absolutely necessary.

And what a treat! Last Saturday was dry (yes, ALL day!!) and mostly sunny and off I was to the Highland Games in North Berwick. This beautiful small town was full of life and on the ground of the games families sat having picnic and I just walked around taking in the scene.
There were so many different competitions that I cannot name but enjoyed watching nevertheless.

I have always had a thing for men in Kilts and boy did I get my money worth that day! They came in all shapes and sizes (and all ages to!)

At the end of the day all the pipe-bands (around 1500 drummers and pipers) marched through the town and the atmosphere was wonderful.

Even though all this piping still rang in my ears when I lay down on my pillow that night, this day was wonderful and I believe Sunday was more productive in my dissertation work than it would have been if I had not taken this day off.

Anna M. Jonsdottir

Wednesday, August 05, 2009

Video: Fire Safety in Tunnels: Are Suppression Systems the Answer?

This is a video of the presentation that was given as part of the Institution of Fire Engineers' "Rasbash Lecture" in June 2009. It is presented in two parts.