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Colour and ignition

Dear Reader,

I saw an interesting demonstration done on the news, channel four news took a lump of thermal insulation of the same type as was used at the Grenfell Tower to a fire testing lab. A sample was sawn off the block and exposed to heat from a heated cone. It looked to me like a Cone Calorimeter. The test used for the TV news appeared to me to be a radiant ignitability test.

The story was in short that the organic plastic had a shiny aluminium layer. When this aluminium layer was exposed to the infra-red light nothing happened. While when the block was turned through 90 degrees to allow the plastic to be exposed to the infra red light without the aluminium layer in the way, the plastic ignited within seconds.

This made me think of something which is well known, there is a <sarcasm>rather cheerful</sarcasm> book on the subject of nuclear warfare with the title “The Effects of Nuclear Weapons” which was edited by Samuel Glasstone and Philip J. Dolan. This is a classic book which was written during the cold war in the USA. It has a chapter (chapter 7) devoted to Thermal Radiation and Its Effects. I think that thermal radiation is one of the most deadly effects of a bomb detonation, it is something which caused a lot of the deaths in Japan so while it might not be as scary sounding as fallout or ionizing radiation it is still a very important issue.

If you look at table 7.35 you will see that the color of cloth alters the amount of energy needed to ignite it. If we consider cotton clothing then white cotton needs a dose of 48 calories per square centimeter to ignite it if the heat pulse comes from a 1.4 megaton air burst. But if we look at the data for dark blue cloth then the energy required to ignite is only 19 calories per square centimeter. The reason I knew about this data was that some years ago I had to assess some work on pyrotechnics and one of the threats I had to consider was an infra-red light induced clothing fire.

I think that the aluminium layer is going to be even more reflective of infra-red light than white cotton. So I think that the cone ignition experiment will have far more difficulty igniting the plastic when the heat strikes the aluminium layer. I saw the plastic and it looked like a pale yellow solid which is the type of color I would expect for a polyurethane foam.

The colour of the foam suggests that large amounts of graphite was absent, I have seen an interesting paper in which it is shown that 15 % of expandable graphite is able to reduce the ability of polyurethane foam to burn according to Sophie Duquesne, Michel Le Bras, Serge Bourbigot, René Delobel, Hervé Vezin, Giovanni Camino, Berend Eling, Chris Lindsay and Toon Roels, Fire and Materials, 2003, 27(3), 103-117. I do not know how much expandable graphite might have helped prevent the fire from spreading but the colour of the plastic suggests it was not present.

Another option would be to use polyammonium phosphate as an additive to the polyurethane, it has been reported that this substance will make it harder to burn polyurethane. I hope to get a chance to write some more about the chemistry of polyurethane.

More on Grenfell cladding and fridge design

Dear Reader,

It appears that a polyurethane type material was present in the cladding at Grenfell, one newspaper is claiming that a product named “Celotex RS5000”. When I looked up this material it turned out to be a polyisocyanate type polyurethane which suggests that it is going to be a bit harder to burn than a simple polyurethane.

The daily mail did print the rather dire line “Insulation burns at sufficient temperatures and gives off hydrogen cyanide”, I would comment that we need to be careful about some words.

Flammable (inflammable) liquid means that the fumes of a substance will ignite if a flame is presented to above the liquid which is below a particular temperture. Flammable solids are a little harder to define, one good definition is a solid which is one of the following

  1. A desensitized explosive which has sufficent water, plasicizer or some other additive to prevent detonation.
  2. A self reactive material which can burn without added oxygen or air.
  3. Solids which can ignite through friction (such as matches)
  4. Pyrophoric solids and solids which can selfheat to the point of ignition.

I very much doubt if the cladding will be able to fall into one of these subclasses, what the cladding is more likely to be is “combustible”. Combustible means “possible to burn the substance if it is subject to sufficient heating”. For example a pool of JET-A fuel will not burn if it is exposed to flame, but if you were to soak a rug in the jet fuel or add a wick then it would be quite easy to start the fuel burning.

The emission of toxic fumes during burning is not a rare thing, many fuels will when burning under the “right” conditions form toxic gases such as carbon monoxide and sometimes hydrogen cyanide. I hold the view that all carbon containing fuels can form carbon monoxide when burnt. Also the generation of hydrogen cyanide during burning under air poor conditions is very common, cigarette smoke tends to contain hydrogen cyanide.

The problem is that all smoke is harmful but smoke from some materials is worse than others, for example overheating PVC and CSPE cables emit fumes which include hydrogen chloride (hydrochloric acid gas). This will make a fire which involves these materials worse than a fire which involves cables such as XLPE cables when we consider how corrosive the smoke is to objects and how harmful it is to people. On the other hand it is important to note that the very chlorine rich plastics such as PVC and CSPE are very hard to ignite. The great problem I see is that if we purge the world of things with chlorine in them like PVC then while a fire might emit less hydrogen chloride once it gets underway we might end up having more fires unless we find a decent replacement.

We need to consider both the frequency (how often) and the consequence of fires and other misadventures. If we look at the Grenfell fire, then if the cladding was the absent from the building then the consequence (how bad) of the fire which started in one flat would have been lower. Removal of the cladding will not reduce the frequency of the fridge fires but it will alter the likely consequence. If on the other hand we were to improve the design / construction of household electric equipment and thus reduce number which burst into flames each year then we could also reduce the number of deaths, injuries and monetary cost per year due to fires.

Back in 2015 the London Fire Brigade published a statement on fridges, what they want is the design and construction of fridges to be altered to reduce the consequence of a fire in a defective fridge or freezer. They want the casing of the device to be metal (to slow the development and spread of fire) or something else which will resist fire better. Sadly again I think that they are misusing the term “inflammable”.

I think that they are right for calling for the fire safety of fridges and freezers to be improved, one of the problems was that in common with PCB transformer oil the freon used in fridges was introduced as a safe non-combustable material to reduce fires. Freon was used originally in fridges as as a non toxic and non combustable alternative to the toxic and flammable gases (such as sulfur dioxide, ammonia and other horrors) which were used in the first ever fridges.

Now instead of things like freon-12 (dichlorodifluoromethane) fridges are using things like cyclopentane, propane or other similar flammable hydrocarbons. I have to ask the question of why do we have to use these compounds. I would like to know if some fluoro-iodohydrocarbon could be devised which would be non toxic, non flammable, too unstable in the lower atmosphere to pose a threat to the ozone layer and unable to cause global warming. But right now we are stuck with fridges which are using flammable gases for their working fluid.

I would like to suggest that we should consider the question of could we improve a fridge in terms of fire safety. I would like to accept the idea that we go for a metal layer covering the plastic foam insulation and we would change to a flame retardant plastic. Such as a layer of XLPE over the polystyrene foam. This would reduce the rate at which a fridge burns. But are there things we could do to stop fridges igniting in the first place.

I would like to suggest that we could change the law to reduce the chances of a fridge creating the spark which ignites leaking gas, for example I would suggest changing the thermostat for one which has all spark generating bits either sealed in a stainless steel capsule, potted in plastic or designed out. This would reduce the danger that a fridge poses if the pipes inside the fridge start to leak. I would also suggest changing to a brushless motor on the compressor to stop the fridge motor making sparks. I would also target the lamp in the fridge, I would opt for a LED lamp which would last the life of the fridge and is in a sealed module designed to prevent a spark encountering flammable gas.

Another improvement would be to add two semiconductor flammable gas alarms. One inside the fridge and one outside the fridge. The idea is that if the one inside the fridge is triggered that an alarm should start ringing and the power should be cut to the fridge. While the second should be outside the fridge at floor level as the working fluids in a fridge form gases which are more heavy than air. If this one goes off it is a more important matter. It should make the fridge scream for help and also shut down. It could also offer a warning in the event of a gas leak in the kitchen (particularly if the people use LPG to run the cooker).

One of the problems is that some words which have very precise meanings within science are used sometimes in the media in places where they should not be. For example “volatile” has two meanings within the Cambridge Dictionary. The second one is the one which is the “scientific” meaning of volatile.

  1. likely to change suddenly and unexpectedly or suddenly become violent or angry.
  2. A volatile liquid or solid substance will change easily into a gas.

But it was used when discussing fireworks, in Malta there has been a string of rather horrible firework accidents. One of the problems is that the firework industry there use pyrotechnic mixtures which are not permitted in many parts of Europe. In one newspaper report it was commented that “local firework factories use highly volatile chemical mixtures banned in many other countries“. Unless the firework makers are using some rather odd mixture such as ammonium nitrate / nitromethane or a low molecular weight organic explosive I would very much doubt if the energetic materials in the fireworks emit a large amount of vapor. Instead what they were meaning is that the firework makers in Malta are willing to use mixtures of things like chlorates and fuels which are very sensitive to static electricity, friction and impact.

It would have been better to have written “the local firework factories use excessively sensitive chemical mixtures banned in many other countries” or “the local firework factories use chemical mixtures which are easily triggered under accident conditions, some of these are banned in many other countries”. I will not go into a deep discussion of firework chemistry here but I will comment that many chlorate / fuel mixtures are unsafe. Some of them are quite rightly banned by UK law and by the laws on fireworks in many other parts of the world.

I have to ask the question of how should we choose the materials for a high rise tower block, we have two issues. The first is how easy (or how hard) is it to burn the material. While the second is how toxic can the smoke be before we decide it is too toxic. Sadly I am unable to give easy answers to these questions.

Mob rule

Dear Reader,

Sadly it appears that mob rule has appeared in the UK, this is in relation to the Grenfell fire. What happened was that a man named Robert Outram who was helping out the people affected by the horrible fire was mistaken for Robert Black. Robert Black is the CEO of Kensington and Chelsea Tenant Management Organisation (KCTMO) which is the organisation which was responsible for the management of the building before the fiery debacle.

It has been reported that a photograph of a man was put on line with the wrong name. Ignoring the fact that the general public should not dispense their own idea of “street justice” what went wrong was that the wrong man was targeted by the mob. I hold the view that while a competent legal system exists to deal with criminal and civil cases that as part of the social contract the public should not attempt to dispense “justice” as vigilantes.

I also hold the view that part of the problem is people who publish information with errors in places such as social media, blogs newspapers and other things. I would urge people to make sure that they check their facts before publication. Some time ago a man who is a “posterboy” for gun control George Zimmerman went and shot a 17 year old named Trayvon Martin. I think that George is a walking and talking argument for “gun control” well at least some form of gun control even if it is not a total ban on the public having guns. The incident when he tried to stop a alcohol inspector dealing with his friend’s underage drinking does raise worries about his fitness to carry a gun in my mind.

Now I do not want to get bogged down in this rather controversial case which has already spawned some lawsuits relating to things like editing of a 911 recording to make Mr Zimmerman look worse.  If you are interested here is another report about that court case. Part of it was dismissed by a Florida judge.

Back to the main issue here, what happened was Spike Lee published George Zimmerman’s address, but he got it wrong ! What then happened was that an innocent family were subject to a series of horrible things. What I would advise people to do is to think before you tweet, blog or post on line.

Think about what you are going to publish.

  1. Is it legal ?
  2. Is it correct ?
  3. Does it serve a useful purpose (rather than your attempt to get your 15 minutes) ?

First lie wins

Dear Reader,

I want to write to you and tell you about a problem, this is a cognitive problem (thinking problem) which many people have. It is that they have a bias in favor of things which they already believe. As a scientist I battle to be the best I can and part of this battle is against the worst aspects of myself. I have to admit that scientists can and do suffer from cognitive biases, I try to work and think in such a way that these biases are suppressed.

I have seen reports which suggest that a polyethene product may have had a key role in spreading the fire so I think it is a good idea I write something about polyethene and fires.  I accept that the important fuel might have been polyethene rather than polyurethane. Maybe for all I know both were present in the cladding.

In the aftermarth of the Grenfell fire polyurethane was mentioned in news reports,  but it now appears that polyethene played an important part in the event. What I have written about polyurethane will stay on the blog, I do not think it is worthless. It might explain to someone something about how polyurethanes degrade and burn.

Now as we suspect that polyethene was a key fuel I want to discuss some polyethene issues, if we confine ourselves to high density polyethene (HDPE) then it is quite a simple molecule. It is simple strings of CH2 units. Here are five polymer chains.

polyethene chains

if we randomly break the chains by heating the polymer in the intense heat of a fire then we can degrade the chains. Now we will have

degraded polyethene

We have a C4, two C6, a C7, a C8, a C10, a C11, three C13, a C16, a C17, a C19, two C21 and a a C22 chain. All of these chains will be much more able to burn than the polyethene. However if we were to use irradated polyethene which is crosslinked then the situation is more rosy. I added some random crosslinks and now we would get the following

crosslinked degraded polyethene

Now we would get a C4, a C6, a C7, a C11, a C13 chain and a lot of crosslinked materials which is much harder to burn. Thus the fire would not burn with the same ease. The cross linking would tend to reduce the supply of fuel to the fire. The plastics fire is fueled by volatile gases which are formed by the thermal breakdown of the plastic, as the fire creates heat this would make it harder to get a self supporting chemical reaction (fire).

There are several methods of cross linking polythene, one method is to use an electron beam irradiation machine. I hope to get a chance to write something about such machines another day.

The problem with the “first lie wins” bias is that it stops people considering new evidence correctly, it also can make people want to defend their pet idea with great vigor. I hope to also have the chance to write more about this as well.

Social Care after the Grenfell Fire

Dear Reader,

It has come to my attention that a claim has been made that people who survived the Grenfell fire are being forced to live under very difficult conditions, as I like to think I am a good scientist I then looked for other reports (from other news outlets) regarding the treatment of the people who survived the fire. I think found this report in a newspaper which suggests that the state has failed to look after these people. While the two reports are not saying totally the same thing, the content of the two do not contradict each other.

The problem I see is that people who are already poor have had to flee with all their ID papers, keys and wallets left behind in the burning building. Surely something should be done to look after their dietary and other needs in the days after this fire debacle. I also have ask how on earth can anyone cope with only £10 a day in London if they have not been able to prepare to have to dash out of their home and not come back.

Regardless of what you think of the Chef Jamie Oliver has did make a kind offer of food and drink to the people. It is interesting that even the right wing “newspaper” (The Daily Mail) has been critical of the response.

I note that during the Vietnam war that when a US airliner (packed with US military personnel) ended up having to make a landing in the Soviet Union that the Soviets did provide them with food, drink and even cigarettes. I hold the view that if the Soviets would do that for a bunch of capitalists during the height of the cold war then surely the UK goverment can do better for the Grenfell residents.

The issue of the cladding has become even more “interesting”, interesting in a rather bad way, with a claim that the cladding was not legal for use for the purpose which it was used for. I am unable to assign blame here as my blog is not a court of law, but this claim if it is true could set the stage for a rather important court case.

More about polyurethane and the Grenfell Tower

Dear Reader,

Regarding the horrible fire in London at the Grenfell Tower, some questions are being quite rightly asked about the safety of using polyurethane foam in the gap between the building and the weather resistant cladding. My first thought was “why not use fibre glass in the gap” as it is a good thermal insulator and it is impossible to ignite (unless one uses chlorine trifluoride).

I saw an interesting comment that polyisocyanate foam would have been safer. This made me consider what is a “polyisocyanate foam”. Before we start it is important to understand what a polyurethane is, it is normally a great big long chain molecule formed by the reaction of a di-isocyanate with a long molecule which has an alcohol at both ends. It is impossible to draw a single structure for polyurethane as many different combinations of diisocyanates and di alcohols exist.

Here is one example of a polyurethane synthesis, I have used polyethylene glycol and bis(4-isocyanatophenyl)methane.

polyurethane synthesis

It has been known for some time that aryl isocyanates oligomerise when exposed to phosphines. A common method of making a polyisocyanurate resin is to take a typical diisocyanate and react it with its self using a catalyst to form a triisocyanate which has a central isocyanurate core. Sorry is this seems like a series of tongue twisters.

resin synthesis

What happens next is that the 1,3,5-tris(4-(4-isocyanatobenzyl)phenyl)-1,3,5-triazinane-2,4,6-trione is reacted with a diol to form a special type of polyurethane. While it is not perfectly noncombustable the hybrid polyurethane isocyanurates are harder to burn than the polyurethanes.

 

Grenfell Fire

Dear Reader,

It has come to my attention that a serious and rather horrible fire occurred recently in an apartment block in London. One of the important questions which need to be asked is “why did the fire spread so fast through the building ?”. A key part of the fire safety case for high rise apartment buildings is that the building is divided into a series of small fire cells. The idea being that a fire in one flat should not be able to spread to another flat or even worse another floor.

The idea is that if the fire can be contained for a long time within one flat that fire fighters will have time to bring it under control while the other people in the block stay inside their own flats. Here in the Grenfell Tower this fire cell idea clearly failed.

It has been suggested that the cladding added to the outside of the building did contribute to the spread of fire, Mike Penning (MP and former fire fighter) has been reported as having commented that the “cladding and windows (were) clearly burning” and that “I have never seen a tower block fire move so fast in that sort of way”.

The Sun newspaper reported that the tower was fitted with a cladding which includes polyurethane, if this is true then I have to ask the question of “why was polyurethane used instead of a noncombustible substance such as fibre glass ?”. I live in a wooden house in Sweden, I have had some building work done on my house recently. I also have to ask “how flame retardant was that grade of polyurethane ?”.

The new walls of my house have a layer of fibre glass in them for the thermal insulation. In my lab at Chalmers I have sometimes accidentally exposed glass wool (fiberglass) to a butane torch while heating glassware using the flame. When glass wool is exposed to this flame it melts slightly but as expected (being glass) it never ignites.

I hope to be able to write something soon which will explain the chemistry of what happens when polyurethanes and polystyrene are heated up in a fire. The key thing to keep in mind is that plastic does not normally burn. It might be a rather challenging statement, but almost no plastics will burn. What happens is that the heat of a fire normally converts plastics into flammable gases and other volatiles, this is a process known as pyrolysis. The pyrolysis products from the plastic then react with the oxygen from the air to burn thus making heat.

One of the key methods for preventing or slowing a fire fueled by plastic pyrolysis products is to slow the rate at which the plastic can emit combustable gases, one method I have seen in the plastic for electrical cables is to use cross linked polyethene. If polyethene (polyethylene) is crosslinked with radiation or a chemical treatment then it is much harder for it to generate pyrolysis gases. I have exposed polyethene to radiation and it does change the properties of the material. Sadly my trusty copy of A.J. Swallow’s book on organic radiation chemistry is out of my reach right now (I am typing on the train).

Another option is to include flame retardant chemicals such as brominated additives and antimony oxide, these substances do get a rather bad press. The problem is that there are some brominated flame retardants such as polybromobiphenyls which are clearly very harmful to human and animal health. But there are plenty of brominated additives such as polubromophenyl ethane and brominated polystyrene which are less harmful. One of the problems is that some elements within the green movement want to ban these substances, the fact that some bromine compounds are bad is not a good argument that all bromine compounds are harmful.

The problem is that it is possible to find harmful substances made from any elements, this is not a good excuse for banning all compounds containing an element. Lets consider a human analogy, “Jack the Ripper” was a human, “Jack the Ripper” was very evil and should have been arrested and locked up to prevent further serious crimes. But this is not a justification for locking up all humans to prevent crime.

What happens when brominated plastic is heated is that hydrogen bromide is released into the fire, this alters the flame chemistry. The hydrogen bromide reacts with some of the free radicals in the flame in such a way that it terminates the free radical chain reaction which occurs in the flame. By adding the antimony oxide this effect is greatly improved, the antimony oxide reacts in the hot plastic with the hydrogen bromide to form water and antimony tribromide. The antimony(III) bromide then has an even stronger fire inhibiting effect than the hydrogen bromide.

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