In article , umpston
wrote:
John Haines wrote in message
...

Don't get me started about the glass. There's nothing wrong with
it, its just a perception.

Remember, the design was carried out when bombs were still going
off in London. One of the JLEP team was very near South Quay when
that went up. We designed for that. We carried out a full risk
assessment for all the glass - I know, I wrote it. LUL has never
formaly got back to us with any criticism, even when a contractor
knocked out a panel and virtually the first people on the scene was
a group of HM Railway Inspectors!

John Haines

Glad to hear there is nothing wrong with the glass (sorry if I'm
getting you started) - but why then is the scaffolding still there?

I have no involvement or contact with the station now so I don't have
any definite information. I also haven't been there for a while so I
don't know exactly what is there now.

I was aware, shortly after the station opened, that there was concern
throughout the network over the possibility of individuals being
prosecuted under H&S law or at least being held responsible for a
prosecution of LUL.

I understood that there had been a number of accidents throughout the
network (about 300 separate locations) relating to glass, fragile roof
materials and falls. The HSE had made it known that they would be
minded to prosecute when the next one happened. No individual manager
wanted to risk being that one so they were all playing very safe. This
in turn created an impression that this was the right thing to do.

There was then talk about adding some additional protection but nothing
was done. I suspect there may be the impression that something will be
done and the temporary protection is thee until that happens.

Incidentally, we did put in some additional protection in two places,
on the NLL platforms. That's what those inverted wire umbrella things
are. (I assume they are still there). They represent the higher risk of
there being someone under that part of the facade.

Glass - yes you have got me started.

To summarise, there are two basic types of safety glass, laminated and
toughened.

Laminated glass has one or more layers of 'plastic' material and does
not fall apart if fractured. In a high energy impact situation, such as
a bomb, that would create a sort of floppy blanket of glass and
significant load would be transferred to the fixings and structure. In
such a situation, the entire sheet would break away and fall as a
quarter ton of glass. The loads transferred to the structure could
cause major structural failure. However, in lower energy impact it
would fracture but stay in place. It would still have to be replaced as
its load-carrying capacity would be reduced.

Toughened glass is heat treated to create a highly stressed outer layer
of glass which makes it typically 5 times as difficult to break. Low
energy impact will not break it. (Lobbing bricks at it, even using the
pinty end of a road spike would not damage it). In an incident with
enough energy to break it, the internal stresses will cause it to
shatter into dice sized chunks, a bit like gravel. This will cause
lacerations if projected at sufficient speed, but is more survivable
that a great blanket of glass or major structural collapse.

There is however a small problem with laminated glass. There are
impurities in all glass. The problematical ones expand over time and
can cause the glass to fracture. Because of the 'locked-in' stress, a
toughened glass panel will shatter explosively. Modern techniques of
heat treatment effectively artificially age the glass to eliminate the
most likely problems but current wisdom says it cannot be ruled out. In
some cases the fragments do not entirely separate, a bit like picking
up a jigsaw by one corner. The wire umbrellas over the NLL are to break
up such fortuitous agglomerations.

I have seen a TV programme where a family who had been under such a
failure in a shopping mall were interviewed. It was not a good
experience, the father was hit on the shoulder by such a chunk, but
they were bruised and a little scratched only.

As I said before, the decision to use toughened glass was particularly
influenced by the risk of explosion. I still think we made the right
decisions for that situation. Laminated glass is most suitable in other
cases. The one action which could make the Concourse a potential death
trap would be to replace the toughened glass with laminated glass.

Fundamentally, if you want light, open, wonderful structures, you have
to accept the (in my opinion very small) risks associated with that.
After all, if it were gloomy, it might increase the suicide rate.

John Haines