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Isocyanates

Dear Reader,

We have had a lot to think about recent regarding polyurethane, so I think it is a good idea if we discuss the chemistry which is the basis of polyurethanes. The key chemicals for making polyurethanes are the isocyanates.

Now for those of you who have never encountered the isocyanates, I can tell you that they are rather reactive electrophiles which are often strong irritants. It is normal to make then from phosgene (carbonyl chloride) and a primary amine. They are similar to both carbon dioxide and the protein synthesis reagent (DCC, N,N’-Dicyclohexylcarbodiimide). All three have a sp carbon in an allene like system.

Using extended Huckel theory we can predict that carbon dioxide will have a charge of + 0.6 on the carbon, while diphenylcarbodiimide will have a charge of + 0.37 on the central sp carbon while the phenyl isocyanate will have a charge of + 0.46 on the central sp carbon. Here is a picture of phenyl isocyanate.

phenyl isocyanate space

Nucleophiles such as water, alcohol and amines will attack this carbon to form addition products. Here is a picture of phenyl isocyanate in which I have calculated the charges on the atoms, these are projected as colours onto the solvent accessable surface of the molecule. The more red they are then the more positive they are and the more blue then the more negative they are.

phenyl isocyanate charges

What you should be able to see is that the carbon in the isocyanate group is the most positive part of the molecule. I have a line drawing for you which will explain what happens when the molecule reacts with an alcohol, which is below.

urethane formation

In this way the isocyanate group can react with an alcohol group to form a bond between the alcohol molecule and the isocyanate molecule. The synthesis of polyurethane normally uses a diisocyanate and a long molecule which has two alcohol groups at the different ends of it. This will allow the creation of bigger and bigger molecules (polymerization) which transforms the small molecules into a very large molecule (a macromolecule).

Grenfell Tower and Browns Ferry

Dear Reader,

We have a problem in life, it is the problem of what is foreseeable. If I was to accidentally summon a giant acid spitting wasp this afternoon by stirring the drums of emulsion paint with a stick held in my right hand, while holding the roller in my left hand while wearing a red boilersuit and sunglasses. Then if this horrible wasp was to lay waste the whole of Vara in Sweden then while this combination of clothing and actions might have made the wasp appear it would be a simple but rather sad accident. An accident caused by complete chance that nobody could have predicted. The good folk of Vara would be unable to sue me for laying waste the whole town as I did not deliberately summon the wasp or do something reckless which made the wasp appear.

On the other hand if it was well known in Sweden that acid spitting giant wasps are attracted to the smell of emulsion paint, the color red and the reflection of light from sunglasses. Then this summoning of the wasp would from a legal point of view be at best the result of a reckless act or worse still the result of deliberate attempt to lay waste the neighborhood.

The question of “would it be reasonable to expect polyurethane foam to burn with great vigor if stuffed into a long tall vertical gap between a concrete building and a metal sheet ?” is one which some prior knowledge exists about. Lets for a moment ignore the other skyscrapers which had serious fires in their cladding, and cast our minds back to the 1970s. Back in the 1970s when I was a very small boy there was a nuclear power plant named Browns Ferry, what happened was a pair of workers were trying to check how good the sealing was with a candle flame. They managed to set fire to the foamed plastic, this fire then spread from the cable room into into the reactor buidling. The fire damaged electrical cables. A short NRC report can be seen on the event here. A nuclear sector trade magazine article on the fire can be read here.

The sealing material used was very combustible, it was a polyurethane foam which was ignited by the candle flame, at the time of testing it lacked the flame retardant coating. Now for those of you who have never set foot in a nuclear site, there is an air pressure issue which we need to know about. It is normal for the air pressure in a contaminated area to be lower than the outside world. I was once standing a few meters from someone who was doing a building modification, the person drilled a hole through a wall. On one side of the wall was a non radioactive area and on the other side of the special wall was a radioactive area. As soon as the hole was made I could hear the air whistling through the hole. The new cables were pushed through the hole and the hole was then sealed up with a sealing substance.

The idea is that if a leak occurs then it is better for clean air to leak into a radioactive area rather than radioactive air to leak into clean area. At Browns Ferry this sucked the flame from the cable room into the ducts taking the cables into the two reactors. I reason that also at Grenfell that a draught would have existed. If a flame exists inside a vertical tube which is open at both the top and the bottom then the warmth of the flame will heat up the air in the tube.

The air will expand and the density of the air is then lower, this will make the air rise up the tube sucking in more air at the bottom. This updraft of air will supply more oxygen to the flame. As a result the flame will become larger and generate more heat. This will make the air hotter, thus increasing the speed at which the air flows up the tube. This can create a strong updraft of air which will increase the rate of burning compared with the same fuel burning in the same burner in the open air.

This will give a similar result to the air flow caused by the pressure difference between the two areas at the nuclear site.

Considering the Browns Ferry fire and the well known effect of a tube on a candle flame (or flame from an oil lamp), I have to ask the question of “was it reasonable to place polyurethane foam in the gap between the wall and the aluminium sheeting“. I think knowing about the Browns Ferry fire and being aware of the chimney effect it is not reasonable to create this sandwich of wall, polyurethane foam and aluminium sheeting.

I think that the creation of a rapidly growing fire was something which is foreseeable. Some of my readers will be glad to know that giant wasps are not possible. Wasps which are the size of humans are thankfully not possible. I am very glad that in one of Clare Smallman’s books she pointed out that the breathing of insects can not be scaled up sufficiently to enable giant killer wasps to live, fly around and menace us. Thus by reading a biology text book as a young boy, Clare managed to preempt any nightmares about overgrown angry insects, thank you Clare !

Well I hold the view that Clare is a “rockstar biology teacher” who is in the same league as “Barry E. Tyler” who is a “rockstar physics teacher”, but we will have to leave these two educational superstars for another day. Sadly both of them have retired so I can not have my dream team of science teachers for my son Jacob.

While hindsight is a great thing which makes everything so perfectly clear, it does seem like a bad idea. I am interested to know if any fire experts who have a deeper insight into fire would be able to argue a safety case that the combination of the polyurethane foam blocks, the concrete wall and the aluminium sheeting was safe. My reasoning is that for a fire expert to argue that the system was safe then they need to explain their reasoning in public without hiding behind jargon. They will need to be able to communicate their ideas and reasoning to “technically-minded non-specialists” if they can argue a case to me that the system was safe I will write about it here. If any fire experts are reading who hold the view that the combination of concrete wall, polyurethane and aluminium sheeting was safe then I would like to invite you to write to me, I am willing to discuss the matter.

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.

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