• Blog Stats

    • 76,804 hits
  • Archives

  • Enter your email address to subscribe to this blog and receive notifications of new posts by email.

    Join 157 other followers

  • Copyright notice

    This blog entry and all other text on this blog is copyrighted, you are free to read it, discuss it with friends, co-workers and anyone else who will pay attention.

    If you want to cite this blog article or quote from it in a not for profit website or blog then please feel free to do so as long as you provide a link back to this blog article.

    If as a school teacher or university teacher you wish to use content from my blog for the education of students then you may do so as long as the teaching materials produced from my blogged writings are not distributed for profit to others. Also at University level I ask that you provide a link to my blog to the students.

    If you want to quote from this blog in an academic paper published in an academic journal then please contact me before you submit your paper to enable us to discuss the matter.

    If you wish to reuse my text in a way where you will be making a profit (however small) please contact me before you do so, and we can discuss the licensing of the content.

    If you want to contact me then please do so by e-mailing me at Chalmers University of Technology, I am quite easy to find there as I am the only person with the surname “foreman” working at Chalmers. An alternative method of contacting me is to leave a comment on a blog article. If you do not know which one to comment on then just pick one at random, please include your email in the comment so I can contact you.

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.

Advertisements

Go on, Have your say !

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: