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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.

DUP views

Dear Reader,

It has come to my attention that Mrs May has been talking about the DUP and the Tories making an alliance. Like many people who do not live in Northern Ireland I did not know much about the DUP so I took a look online and asked my legal advisor about them. I found out a list of things which senior members of the DUP have been accused of having said. Newspaper reports support these claims which have been made about their statements. When I searched on line for evidence to support some of their claims, I very quickly found newspaper articles supporting the claims made by others.

  1. Abortion should be “ruled out for rape victims”
  2. The Pope is the Anti-Christ
  3. Gay couples “more likely to abuse children
  4. Homosexuality is an abomination
  5. No gay marriage (also see this)
  6. Gays more vile than child abusers
  7. Attempts to reduce CO2 emissions are “Green propaganda
  8. Man-made climate change is a con
  9. Creationism should be “taught in every school”
  10. The 60 million-year-old Giant’s Causeway is only 6,000 years old
  11. Line dancing is “sinful”

As a scientist I can not deal with many of the points, but 7, 8 and 10 are ones which I can deal with. If we consider 10 then we can address this point using radioactivity calculations. If we examine zircon (zirconium silicate) crystals from rocks we can estimate their age.

Zirconium silicate is a mineral which strongly rejects lead when it forms, so it will be lead free when it forms. Before we start we can look at what is in the unit cell of zircon. The unit cell is an important but tiny building block of a solid. I obtained the cif file from here. The unit cell is tetragonal, it is cube which has been compressed in one direction. Thus it is a box which is 6.607 by 6.607 by 5.982 Å. One Å is 0.1 nanometers. Here is a picture of what is in the cell.

zircon cell balls and sticks

The silicon atoms are yellow, the green ones are zirconium while the red-orange ones are oxygens. When the zircon crystals form the lead content is zero as lead does not incorporate into them but thorium and uranium can incorporate into the crystals.

At the start the lead content of the zircon is zero, as the uranium undergoes radioactive decay lead is formed. Using a simple equation it is possible to work out the age of the rocks by comparing the amount of uranium and lead in them.

For uranium we use

NU = NUo e t

and for lead we use

NPb = NUo (1 – e t)

Now armed with these equations we can work out how the uranium to lead ratio will change as a function of time.

While I do not have data for the Gaint’s causeway, I do have data for south east Ireland, I doubt if the rocks there will be very different to the rocks in Northern Ireland. Here the 206Pb:238U ratio was about 0.07:1.00. The 238U decays into 206Pb via 226Ra. Thus 0.935 of the original 238U is left in the zircon crystals. I got the data from “Select Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite. Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite V.” Gallagher, P. J. O’Connor, M. Aftalion. Geologcal Magazine, 1994, volume 131, issue 5, pages 669-684. DOI: https://doi.org/10.1017/S0016756800012450.

The half life of 238U is 4.468×109 years, thus the decay constant for this nuclide is 1.551 x 10-10 years-1. Now we have to rearrange the formula for the fraction of the uranium atoms which are undecayed.

NU = NUo e t


NU / NUo = e t

-ln (NU / NUo) = λt

-ln (NU / NUo) / λ = t


-ln(0.935) / λ = 0,06720874969345005314173683498865 / 1,551 x 10-10 years-1 = 433.325 x 106 years.

So we have a age for a rock formed by a volcano in Ireland which is about 433 million years old. Now while the person from the DUP have made a comment about rocks in Northern Ireland I am sure that rocks from the Republic of Ireland of a similar type will have a similar age. Now I hope that you can understand that the rocks of both the Republic of Ireland and Northern Ireland are much older than 6000 years.

I also have to ask the question of does it matter to a religious person if the earth is older than 6000 years. I know that Bishop James Ussher estimated that creation occurred in 4004 BC, but how much does it matter. I also have to ask “Is an all powerful God any less able to help the humans sort out their lives if they were descended from monkeys and other lifeforms ?”

I know that many people hold the view that “science has replaced religion”. I would strongly disagree with this statement. Science and religion normally deal with different questions.

In the same way that I think that it would be ridiculous and ill advised to attempt to prove (or disprove) the existence of god by means of a science experiment, I think it would be the height of folly to attempt to solve a chemistry, physics or biology problem by reading the bible. I know some chemists who are deeply religious, for their their faith and their science are able to coexist in their minds.

London attacks

Dear Reader,

It has come to my attention that a group of men drove a white van into people last night at 10 pm UK time (11 pm Europe time) and then carried out a knife attack. I will not attempt to try to compete with the news outlets such as the BBC, the reason is that Dr Foreman does not have a large team of people writing and looking around for information.

I am deeply troubled and unhappy that a group of people should choose to commit such an outrage. I have to ask the question of how can a person make the whole world convert to a religion if they murder everyone who does not practice their religion ? I imagine that the world would become a very empty place if this was taken to its perverse conclusion. I know that people differ in their views and opinions, normally I think that a better way to get the world to agree with you is to persuade people using facts and good arguments for why they should agree with you rather than attempting to change opinion by violence and threats.

What I find interesting and disturbing is that Donald Trump has been reported to have called for a travel ban as a response to the event. I have to question the wisdom of such a ban, Trump wants to restrict travel from 6 countries which are mainly muslim for “national security” reasons. I have to ask if such a travel ban would do any good as terrorists often are willing to break the law and travel using false papers.

Equally troubling I have discovered that some people in the UK are calling for the election to be canceled. One Mark Oxley has been reported by the Daily Mail to have started a petition with the words “to call off the general election for the foreseeable future”. I think that it would be wrong to cancel the election for a series of reasons.

  1. While the event in London is deeply offensive and an attack on British society it is not a sufficient threat to require that democracy be suspended. The IRA bombing and shootings in the past did not make the UK give up democracy, so why should we now give up on it !
  2. Aborting the election would give the terrorists a great victory, they would know in future that by means of violence they can make the British give up on democracy.
  3. The police, security services and the military may be needed to prevent or to mitigate terrorism, the operation of these three things will not (and can not) be changed quickly on a day to day basis by the goverment in Whitehall.

I would suggest that the UK should go ahead with the election later this coming week.

Karlstad fire

Dear Reader,

It has come to my attention that a large fire occured this afternoon in Karlstad in Sweden, this fire occured in an industrial site on saturday afternoon. In some ways this is the best time / place to have a fire as fewest people will be close to the blaze.

When I find out more about the fire I will post more about it.

Gun safety

Dear Reader,

It is the “end of school” time now, and I am sure many schools are now finishing for the year. There are lots of people who are now finishing school and they are getting ready to move on with the rest of their lives. Sadly in one case a young lady will not be moving on with her life to new and interesting things. She is dead, her boyfriend shot her in the torso in an “accident” with a new gun.

I have to ask the question “was it a true accident ?”, I hold the view that very few gun accidents are events which are truly outside the control of the person owning or holding the gun. In some ways a gun is a very safe object, it is a length of metal pipe. An unloaded gun could be used to knock nails into walls (if you do not care about the damage to the gun that you might do if you use something like a revolver as a hammer). But a loaded gun is a rather dangerous object.

I strongly in favor of drop tests for guns which are likely to be carried while loaded and other tests designed to check to see if such guns will discharge when dropped or otherwise abused. I hold the view that in common with X-ray and industrial gamma radiography equipment that guns / holsters should be designed such that a single inadvertent act can not issue forth bullets or gamma / X-ray photons. One which I think is a smart design is the “grip safety” which is used on some pistols intended for police officers. The idea is that unless a human hand is holding the gun it can not function. For example the french MAB pistols had this feature. Sadly I have never heard of a “nonidiot safety“, this would be one which disables the pistol unless it is being held in the hand of a sober, sensible adult.

I would like to suggest that Twitter should be fitted with an anti-idiot lock, also hold the view that the US goverment needs a similar idiot lock. I find it interesting that their current president is using devolved powers to reject a treaty on climatic change. But I find it interesting that Mr Obama used similar powers to avoid having to use the US parliament for ratification of it. But two wrongs do not make a right, if I was to have a good reason to want the USA to withdraw from the Paris Agreement I would want to do it via their parliament (house and senate) rather than using a devolved power as it is harder to challenge the use of parliament than the use of devolved power and for public relations reasons. But now back to the topic of gun safety.

But even a gun which can not pass a “drop test” will not discharge a bullet if it is dropped when it is unloaded.

I know that guns divide opinion very strongly and some people feel such a strong attachment to their guns that they will resist any attempt at gun control (both unreasonable and reasonable curbs on the ownership / use of guns). But Mark Foreman PhD is able to issue a proscription that will prevent the vast majority of gun mayhem caused by “accidents”. I hope that my advice will be acceptable to both the antigun lobby and the pro gun lobby. I hold the view that Smith and Wesson, Colt, Winchester and the NRA want to avoid accidents with guns.

1. Never point the thing (loaded or otherwise) at other people, animals, valuable property, pets or yourself. Always keep it pointing in a safe direction such as into the floor, into a solid stone wall, a bank of earth or at an oil drum filled with sand which is standing in front of a concrete wall. OK we will ignore the moment when hunting when you might point it at that deer or wild bore.

Now lets assume that your gun goes off “by magic” while you are pointing it in the safe direction. Then if we consider a single 38 bullet then according to a recent test it will pass through about 6 inches of pine wood. Even if the bullet manages to pass through 6 inches of pine it will be travelling much slower and thus will be less likely to cause death / serious injury if it hits some random person. For higher energy pistol bullets and rifles I would expect them to be more able to pass through pine wood and other building materials.

2. Treat all guns as loaded until you know otherwise.

When you pick up a gun assume that it is loaded until you check for yourself that it is not. If you do not know how to do this, then either have nothing to do with guns or learn quickly how to safely check if a gun is loaded or not.

Irresponsible leaking of information

Dear Reader,

When I read the Guardian this morning it come to my attention that Mike McCaul in the USA has made a statement regarding the explosive which the Manchester bomber used. He stated that the bomb contained acetone peroxide. I think that this was a very bad thing to do as it limits the ability of the British authorities to deal with the criminal or criminal network which is behind this outrage.

I am not sure quite how fast the forensic workers can work, I also wounder how accurate the results which he leaked were. Fox news has claimed that a bomb making workshop was found during a raid recently,

I have to also ask the question of “need to know”, what does the public need to know about the bombing. The public should be told that a bombing has occurred and that the police and other parts of the state are dealing with it. But I would argue that the public do not need to see photographs of the wreckage from the bomb or know technical details of the bomb at this stage. I have to ask the question of what good does it do to tell the public the identity of the explosive.

I can not see a reason or purpose right now, I could understand it coming out during the trial of a bomber. My own view is that the trials of bombers should occur in open court, but during those sections of the trial when the design of the bomb is discussed these sections should be held in camera. My reason is that I would rather that the next generation of bombers do not get an education on bombs by attending (or reading about) a trial where bomb design is considered and discussed.

Now the cat is out of the bag, I see no point in not discussing some aspects of the explosive here. The explosive in question is a rather rare one, it is nitrogen free. Many explosives (TNT, ANFO, Picric acid, RDX, nitroglycerine) contain nitrogen. One of the driving forces for the detonation is the formation of nitrogen gas. A typical explosive contains both a fuel and an oxidant. In the case of TNT the fuel is the methyl group and the aromatic ring while the oxidant is the oxygens in the nitro group.

In the case of the London Tube / Bus bombings and the Manchester concert bombing it appears that the bombers used combinations of an organic fuel and peroxides to build their bomb. In the interests of public safety I will not be giving any details of how to make explosive organic peroxides. I hold the view that the UK is going in the right direction with the law on explosive precursors (Control of Poisons and Explosives Precursors Regulations 2015). This law restricts the sale and possession of chemicals such as hydrogen peroxide. The current limit in the law for hydrogen peroxide without a license is 12 % w/w. This is a rather strong solution compared with what is needed for bleaching hair and other household uses.

If we assume that the density of 12 % hydrogen peroxide is 1 gram per ml, then 1 litre of such a solution will contain 120 grams (3,53 moles) of hydrogen peroxide. This would generate 1.76 moles of oxygen gas if it was decomposed totally which would have a volume of 42 litres. An old fashioned way to express the concentration of hydrogen peroxide is to state the number of litres of oxygen which would be generated by the total decomposition of 1 litre of the hydrogen peroxide solution. When I was a boy I used to buy 30 vol hydrogen peroxide to use in my chemistry experiments which I did in the shed. I had set out to buy 20 vol hydrogen peroxide but I found out that the chemist sold 30 vol hydrogen peroxide instead. I once bought some 50 vol hydrogen peroxide, this would now come under the UK law which I mentioned above.

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