Fire without flames : 13 amazing facts aboutsmouldering fires

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Fire without flames –

13 amazing facts about

smouldering fires

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Abstract

This FRIC report presents a popular scientific overview of 13 facts about smouldering fires. The aim is that the reader will get an insight into why these fires fascinate, their challenges and consequences, and how to extinguish them. The 13 facts are on the following topics:

1. Fragmented knowledge 2. Nicknames

3. Peat and coal areas - a worldwide challenge 4. Peat fires in Indonesia

5. Burning Mountain of Australia 6. Wood pellets silo fires

7. Fire deaths caused by smouldering fires 8. Coal fires in China

9. World Trade Center 10. Smouldering in space 11. Zombie Fires

12. Titanic

13. Fighting flameless fires

The report is complemented with an interactive, online presentation which may be found here:

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1 Introduction

The purpose of this report is to give a popular scientific overview of smouldering fires, why they are fascinating, their consequences, and how to extinguish them. The content of this report is also presented in an interactive, online presentation which may be found here:

https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

In this report, screenshots from the online presentation will be presented along with more detailed information on each topic, to encourage utilization of the online presentation in parallel with reading the report.

The hope of the authors is that this report may give a valuable overview of interesting facts about smouldering fires for everyone who wants to get an insight into this fascinating topic.

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2 Facts about smouldering fires

The technical term for a fire without flames is smouldering fire or smouldering combustion. This is a slow, flameless burning of fuels during an exothermic reaction. Smouldering normally occurs at low temperatures (relative to flaming fires) and the oxidation takes place at the solid phase. Depending on the combustion temperature and how one defines smouldering, glowing combustion is also sometimes included under this term. The smouldering process consists of a few main, global processes: first drying, followed by preheating and then pyrolysis and oxidation. These may in turn be divided into countless interlinked chemical and physical reactions. Common materials which are known to smoulder are for example wood and cellulosic products, mineral fibre with organic binders, cork, paper, leather, cotton, carbon, forest duff, cacao powder, peat and organic soils, various agricultural products, latex foam, some types of polyurethane, coal and dust layers of various sort. [1]–[3]

Smouldering fires are relevant for all areas of society - domestically, industrially and environmentally. During recent years, smouldering fires have gained more attention, as demonstrated by an increasing amount of scientific publications on the topic (although the total number is still low, see fact 1). There is also an increased focus on the topic at European level, as demonstrated for example by EN 16733 [4], first published in 2016, on building products' propensity to undergo continuous smouldering. Environmentally, there has also been an increased focus lately on the global smoke emissions from smouldering fires, for example from peat fires and their contributions to regional haze incidents [5], see more information in fact 4.

Figure 2-1 Screenshot from the online presentation of this report, on the basic knowledge of smouldering. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 1 on Fragmented knowledge

Smouldering fire research has a great potential and is not yet as well understood as flaming fires. An online search showed that only 0.8% of the scientific articles related to “fire” on Google Scholar are on smouldering fires, while flaming fire is a much more common focus area with 9% of the hits.

This shows that more experimental and theoretical studies and multidisciplinary research on smouldering fires are necessary and could explain why the knowledge about smouldering fires is so fragmented.

During the making of this report, and during the work on previous studies on the topic [3], the authors have found that even within the fire science community, there are different opinions on whether or not glowing fires are indeed an under-category of smouldering fires, or if these are two separate (but linked) phenomena. The authors have come to the conclusion that most likely, glowing fires are a part of smouldering fires as a phenomenon, but find it interesting that there is a discussion about such a basic point within the field. This is an example to demonstrate the fragmented knowledge, and the need for more studies on the topic.

Figure 2-2 Screenshot from the online presentation of this report, on the number of articles of flaming fire in comparison to smouldering fires, which is one reason for fragmented knowledge. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 2 on Nicknames

Smouldering fires have a multitude of different names. Scientists within one field (e.g. earth systems science) use descriptions that are significantly different than scientists in other fields (e.g. fire science), to describe the same phenomenon. An essential part of understanding smouldering fire is to know what it is called in the different fields and what nicknames it has.

In the context of the melting Arctic, it is called Zombie fire [6], for peat fires, it is often referred to as underground fire [7], but it has many more names such as the smoking problem [2], glowing combustion, non-flaming combustion, oxidative pyrolysis, filtering combustion, low oxygen combustion, deep-seated fire, hidden fire, lagging fire, smoking material, in-situ combustion, fireflood and underground gasification [8].

The fact that researchers from various fields and disciplines have given different names to the same phenomenon may also lead to fragmented knowledge and makes literature search more difficult.

Figure 2-3 Screenshot from the online presentation of this report, on the nicknames of smouldering fires. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 3 on Peat and Coal areas

Smouldering fires are not local phenomena for only one or two regions of the world. It is a worldwide phenomenon and thus a global challenge [9], [10].

The resulting emissions affect us all. It is therefore essential to work towards an effective and efficient solution. Peat and coal areas are shown below. The following two facts deal with two of these affected countries, Indonesia and Australia.

Figure 2-4 Screenshot from the online presentation of this report, on the peat and coal locations of the world. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 4 on Peat fires in Indonesia

As shown in fact 3, peat fires are a worldwide problem. Especially affected is Indonesia because it contains 36% of the world’s tropical peatland [11]. Peat consists of decomposing plant material and organic matter. Peat fires are smouldering fires and therefore an incomplete combustion process. As every smouldering fire, peat fires are difficult to extinguish and they may spread underground in peat layers [5]. The National Agency for Disaster Preparedness (BNPB) have called peat fires «crimes against humanity» [12]. This points out how large and dramatic the consequences of peat fires are.

Peat fires occur annually and are particularly large when the peat fires occurred at the same time as the El Niño dry season. Some recent, large peat fires in Indonesia in 1997, 2015 and 2019 will be presented here as examples.

The fires in 1997 was mainly during August to mid-November. The official cause of the fires was controlled fires that spread out of control. In total, an area of 7.295 square kilometres of peatland was burned. This is more than half the size of the Bahamas. The consequences affected not only Indonesia, but the whole world. The fires released 0.19 - 0.23 billion tons of carbon to the atmosphere, the smoke impaired visibility so severely that air traffic had to be stopped in Indonesia. The smoke cloud covered large parts of South-East Asia, even Australia and China were affected. [8], [13], [14]

During July to October 2015, another large peat fire occurred. This time the cause was the tradition of clearing the forests with the fire during the dry season. The burnt area more than tripled in 2015 compared with 1997. The burned area was 26.000 square kilometres, which is more than half the size of Denmark. The total emissions of burnt peatland and forest fires amounted to 1.6 billion tons of CO2. Reported consequences included more than 90.000

premature deaths due to respiratory disease and other sickness. The smoke also affected air traffic and reduced visibility. [15]

The peat fires of 2019 burned an area of 16.000 square kilometres. This corresponds to the size of Belgium. Farmers and pulp producers were mainly held responsible for the fires, as they use the slash-and-burn method to clean the land and replenish the soil. During the fires in 2019, about one million people suffered from acute respiratory tract infections, the health of 10 million children was found to be at risk and around 708 million tonnes of CO2 were released into the

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Figure 2-5 Screenshot from the online presentation of this report, with an overview of the recent, large Indonesian peat fires. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

After the devastating fires in 2015, the Indonesian government has made efforts to protect and rebuild the peatlands by regulating the cellulose producers, to protect and rebuild peatlands. Since this, these regulations have already been relaxed. The largest cell and paper manufacturers still use areas of burned peatland for production, rather than rebuilding the peatlands and practically nothing has changed. [16]

There has also been a recent focus in the scientific community to study and understand peat fires. One example is the GAMBUT project. The abbreviation stands for Generating Anticipatory Measures for Better Utilization of Tropical Peatlands and it is a United Nations Environmental Programme (UNEP) Project. The establishers of the project are the Government of Indonesia, UN Office for Project Services (UNOPS) and the US Agency for International Development [17]. The aim of the project is to reduce the number of burning fire hotspots and the amount of emissions, to improve the abilities of provincial and district-based fire coordination centres and the use of early warning systems for fires. They also want to change the response-orientated fire management system to a comprehensive and integrated fire risk mitigation system. The initial results are training for hundreds of officials and communities that are better prepared for the fire season. [18]

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Figure 2-6 Screenshot from the online presentation of this report, on what the Indonesian government and the scientists have done since the peat fires of 2015.

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Fact 5 on the Burning Mountain of Australia

Smouldering fire is not a new phenomenon, and these fires may also be tourist attractions. A good example is the oldest, continuously burning fire in the world: The Burning Mountain of Australia. This coal fire has been burning for ca. 6000 years, moving slowly at a rate of about one meter per year. The burning mountain of Australia is located in Wingen, New South Wales. It has two chimneys and the larger one is known as the Burning Mountain. The smoke leaving the chimneys can be seen from distance. It is assumed that the hot area is about 400 square meters, located well below the top surface [19]

Coal fires are smouldering fires that occur in underground or exposed coal seams, coal storage piles and coal waste piles. They can ignite spontaneously at temperatures around 80°C. Also, external factors such as mine gas explosions and careless handling of waste can lead to ignition. Coal fires are a worldwide phenomenon, just like peat fires. They are grouped according to age, reason, place and progression. [20]

Figure 2-7 Screenshot from the online presentation of this report, on the tourist attraction and oldest continuous burning coal fire, the so-called burning mountain of Australia. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 6 on Wood pellets silo fires

Industrially, smouldering fires are not a rare occurrence, are problematic for large scale storage of biomass and bioproducts, for example in flat storage units or in silos. Here, smouldering can ignite spontaneously and spread slowly, often unnoticed for long periods of time. Extinguishing these fires is a very challenging task. One example is the smouldering fire in a wood pellet silo of Hallingdal Trepellets, which is located in Ål, Norway.

On July 5th_{2010 shortly after midnight the fire brigade was called to a smouldering fire. The 7742}

cubic metre silo was about half filled with wood pellets. The sensors in the silo had measured an increase in temperature. Since the requested nitrogen gas tank truck was not able to arrive until noon, the fire brigade decided to request 22 CO2 cylinders from nearby facilities. The silo had

reached a temperature of 60 °C at this time and smoke was not visible at the roof. The cylinders had a volume about 220 cubic meters of CO2, corresponding to only 5% of the headspace volume

above the pellets in the silo. The arrival of the nitrogen tanker truck was delayed to the mid-afternoon. Due to this information it was decided to manually inject the CO2 into the silo to lower

the oxygen level. During the discharging of the 5th_{cylinder, the silo exploded. The force of the}

explosion lifted the 27 tons roof and flames came out. The firefighters suffered only minor injuries. After the explosion the silo could no longer be used, and the walls were torn down to empty the silo and extinguish the remaining pellets. An important learning point from this incident, in particular for emergency responders, is the importance of being aware of the hazard of electrostatic effects, which can make the suppression of smouldering fires in silos with CO2

potentially unsafe. [21], [22]

Figure 2-8 Screenshot from the online presentation of this report, on a silo fire in Norway at the 5th July 2010. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 7 on Fire deaths caused by smouldering fires

It is difficult to make a generally valid statement of the total number of fire deaths due to smouldering fires, since they can transition to flaming fires, and the evidence is consumed by the flaming fire. [23]

US statistics show that smouldering is the leading cause in residential fires [24], nevertheless the danger of smouldering is often underestimated. As mentioned previously, a smouldering fire is an incomplete combustion, producing a high yield of CO, in addition to other toxic smoke gases [8]. The majority of fire deaths are therefore due to asphyxiation or other toxic effects, rather than because of burning. This excepts if a person is located in a room with a flaming fire, in which case, the toxic gases are of secondary importance and the heat poses a greater hazard. [25] Fire statistics from 2006-2016 shows an encouraging decreasing average number of fire deaths per 100 fires [26]. It is essential to establish an awareness of the danger of smouldering and smoke in the population.

Figure 2-9 Screenshot from the online presentation of this report, on fire deaths caused by smouldering fires. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 8 on Coal fires in China

There are about 200 coal fires in China that produce 2-3% of global CO2 emissions annually.

Around 100.000 to 200.000 tons of coal burn annually due to unintentional coal fires. This leads to an economic loss of 80 to 130 million US dollars for the Chinese coal industry. The losses are linked to the loss of the product (coal) and also to production interruption due to the fires. The main regions are Wuda, Ningxia and Xinjiang. Previous attempts to extinguish the fires, such as digging out the burning coal or closing all openings with sand and liquid foams, have been found to be dangerous and only successful if well planned and subsequently observed. A possibility is being developed to inject CO2 into coal fires to reduce the oxygen content and extinguish the fire.

This project is being carried out in cooperation with the Norwegian company Sargas. [9], [27]

Figure 2-10 Screenshot from the online presentation of this report, on the coal fire areas in China. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 9 on World Trade Center

Every year on September 11th_{there are numerous documentaries on the World Trade Center}

disaster. Often it is not mentioned that it smouldered in the debris for more than 5 months. The final extinguishing of the smouldering fires was only possible during the final removal of all the debris. [2]

The smouldering fires caused large smoke emissions, and only after 200 days did the pollution levels in Lower Manhattan return to normal urban levels. This means that for more than half a year people were exposed to a significantly increased level of pollution. These smoke and dust particles also penetrated into the surrounding houses. The long-term consequences include the risk of decreasing lung capacity and “WTC cough”. [28]

This smouldering fire shows why it is important to develop suitable and as safe as possible extinguishing methods. A long-lasting smouldering fire in a large city will have a direct impact on the lives and health of many people.

Figure 2-11 Screenshot from the online presentation of this report, on the smouldering fires after the World Trade Center tower collapse.

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Fact 10 on Smouldering in space

Smouldering fires are an interesting phenomenon not only on earth but also in space, since the fires in space may behave differently and could affect fire safety of space facilities such as the International Space Station (ISS). NASA has therefore conducted smouldering combustion experiments under microgravity, which have been useful for a fundamental understanding of smouldering. In addition to being useful for safety in space, microgravity offers the unique ability to test truly one-dimensional flow experiments in combustion science. Such conditions provide less complex and more idealized boundary conditions for experiments, and thereby enables researchers to get a better, fundamental understanding smouldering. [2], [29]

Figure 2-12 Screenshot from the online presentation of this report, on smouldering in space and the reasons why NASA deals with the topic.

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Fact 11 on Zombie Fires

Zombie fires have already appeared in the nickname overview in fact 2. As expected, a smouldering fire is hidden behind the nickname. But one thing that makes it special is that it can survive winter and pop up in spring at a new location in the Artic nature sub-surface – like a zombie, neither dead nor alive. A significant problem of global warming is melting of the Arctic. The area warms up twice as fast as the rest of the world. Boreal forests and Arctic tundra cover 33% of the world's land surface and store 50% of the world's soil carbon. The smouldering fires make fixed carbon to be emitted into the atmosphere. This leads to a dramatic increase of carbon in the atmosphere and the process is accelerated. These smouldering fires are very difficult to extinguish and no solution has been found yet. [6]

Non-arctic areas also have underground smouldering fires, as illustrated in Figure 2-13.

Figure 2-13 Subsurface or underground fires which have been initiated at one location may reappear at a different location months later. Figure from [2], reused with permission.

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Figure 2-14 Screenshot from the online presentation of this report, on the Zombie Fires in the Arctic. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

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Fact 12 on Titanic

Everyone knows the story of the Titanic. A recently presented hypothesis is that the iceberg is not solely responsible for the sinking of the Titanic. The background is that there seem to be evidence that there was an ongoing smouldering fire in the coal bunker, and that this was responsible for the instability of the metal skin and the damage to the structure. When the ship hit the iceberg, the fire may therefore have accelerated the sinking process. [30], [31]

Figure 2-15 Screenshot from the online presentation of this report, on how smouldering plays a role in the story of the Titanic.

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Fact 13 on Fighting flameless fires

One central question that arises in connection with smouldering fires is how to extinguish them. But before extinguishment may start, detection of an ongoing smouldering fire is necessary. This may be challenging, since smouldering fires can be very difficult to detect. Even though a smouldering fire produces high yields of toxic smoke, the combustion rate is very slow, and therefore the emission per time unit is low. In addition, the buoyancy of the smoke is weak, meaning that the smoke will not rise quickly upwards, and the smoke may never reach the position of the detector, as this often is located in ceilings. These smouldering fire properties makes detection challenging. [8]

Once detected, three common methods to extinguish these fires are extinguishing with water, gas quenching and cooling [3]. The consequences for the industry in terms of health, safety and economy are similar for all methods. Any removal of fuel for complete extinguishing implies the presence of personnel, and injuries may occur due to asphyxiation, inhalation of toxic gases, flaming fires or explosions. The extinguishing of a smouldering fire is a slow process and can lead to a production stop. This in turn means a higher economic loss for the company. After extinguishing, the fuel is no longer usable or saleable. The economic loss is also given here.[3] The use of water is the most popular firefighting strategy. For this to be efficient, a direct access to the smouldering material is needed. For silos, this often requires a manual and destructive opening of the side walls, or access from the top which often is inefficient for extinguishment purposes. When using water, it must be taken into account that compressed fuel can change its volume and swell. This may result in the structural integrity of the storage facility being damaged by additional weight of water and the risk of rupture. In addition, a large amount of water is required, between 1 - 6 litres of water per kilogram of smouldering coal or peat is needed. [3], [32], [33]

Besides the use of water, gas extinguishing can be used. It is mostly used as a transitional solution to control the fire, as it may takes days to months until complete extinguishing by gas quenching. The penetration of gas at industrial units without pre-installed gas suppression systems is insufficient for complete extinguishing. Once the gas is turned off, there is a risk of re-ignition. In addition, if inert gases are used, the lowered oxygen content in the facility represents an additional hazard for personnel and emergency services. [3]

A distinction must be made between direct and indirect cooling. Direct cooling is for example pouring water onto a burning unit, with the disadvantages this has. By indirect cooling, one avoids the typical challenges with water, such as swelling, scattering and water run-off. Cooled liquids pumped through a pipe positioned in the fuel bed can absorb the heat and could thereby prevent ignition or potentially be used as an active suppression method. A challenge with the method industrially is that the location of the pipe does not necessarily correspond to the location of the smouldering fire hot spot [3]. Indirect cooling has not yet been researched on a large scale and further investigations are necessary.

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Figure 2-16 Screenshot from the online presentation of this report, on the different ways to extinguish a smouldering fire. https://prezi.com/view/yVFHODruMbxK3e9yMLkF/

3 Final words

In the Fire Research and Innovation Centre (FRIC),

We work to increase fire safety and make your day safe [34]

As part of this work, FRIC deals with the topic of smouldering fires as part of project 2.2 – smouldering: effects of cooling. Indirect cooling of smouldering fires, using water cooled pipes inserted into the smouldering zone is a central part of the project and will be studied using experimental and numerical work.

Another part of the project is to collect and spread existing knowledge on smouldering fires. With increased knowledge, we hope that smouldering fires can be seen not only as the boring little sibling of flaming fires, but as a fascinating phenomenon and important topic for scientific studies and societal focus.

If you have questions about this report, or input on the topic, please do not hesitate to contact us, please see https://fric.no/en for contact details.

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Fire without flames : 13 amazing facts aboutsmouldering fires