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DJE
post Jun 3 2016, 10:07 PM
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In 2009 an inflatable art installation in Harlow was blown away by the wind killing 2 members of the public who were inside.

Only 2 months ago a child was killed when the bouncy castle she was on was blown away in high winds.

The cardboard castle erected in the Market Place probably weighed a few tons, and only lasted a few hours before the wind blew it over. Luckily no-one was hurt, even though it fell outside the 'safe' area demarcated by tape.

It was tethered to four 1-ton weights. It is not clear to me whether the tethers failed, or the weights themselves were inadequate. The castle had a surface area similar to that of wings of an airliner, so it takes little imagination to realise that wind could exert forces of many tons on such a structure.

Artists building such structures seem to be totally out of their depth when it comes to basic engineering. Is the H&SE looking into this?
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On the edge
post Jun 4 2016, 07:10 AM
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The HSE could have a field day round here. We've got kids running round in a slippery wet play area without hi vis, helmets or shin protection. Worse, they are encouraged to run free near an open deep waterway; which with its ducks naturally attracts them. I'm not sure it is a particularly good idea to hang a heavy sometimes damp cloth on a long pole attached to an apparently crumbling old building over a busy footpath. Nonetheless, in this case, as specific permission from the authorities must have been obtained, a full risk assessment would have been demanded. What happened, happened. No one was hurt and no damage done so the assessment must have worked.

Think about it, the saddest thing about this incident will be the effect it has on any future innovative suggestions. Ooooh no, can't do that round here, we don't have ideas or do innovation. Newbury, where mediocrity passes for merit.


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Simon Kirby
post Jun 4 2016, 11:10 AM
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QUOTE (On the edge @ Jun 4 2016, 08:10 AM) *
Think about it, the saddest thing about this incident will be the effect it has on any future innovative suggestions. Ooooh no, can't do that round here, we don't have ideas or do innovation. Newbury, where mediocrity passes for merit.

In fairness, it did happen, and I'm as surprised as you as I don't think of Newbury as innovative or imaginative, but for me it was an absolutely tremendous event, not simply because it was so spectacular, but even more for how it engaged the ordinary Newburians in something so funky and public, and dare I say it, civic.

As for the HSE I can't see that the collapse is RIDDOR reportable and as no one was injured I doubt that they would have the time or inclination to scrutinise the adequacy of the risk assessment.


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On the edge
post Jun 4 2016, 12:22 PM
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Actually, I was simply reflecting on DJE's opening post which was, in my view, wholly negative. Not a word about the interest and dare I say joy in generated for the ordinary Joe. It was unusual, different and a very unusual thing to stage on top of being a very good artwork - generated by people working together. However, on here, our opening comment is 'Ooooh it's dangerous'; so, if that is reflective of Newbury opinion generally, it's hardly surprising that our elected representatives adopt the same attitudes.

Yes, there is a safety point and yes a problem occurred. Again, it's rather ironic that even with the rather expensive bureaucracy officialdom tends to impose on any event, there are still gaping holes and accidents. It is this stifling bureaucracy that provides a false sense of security and makes all involved believe safety is someone else's responsibility. Given their passionate interest in safety and obvious knowledge, could DJE let us know what was said when challenging the organiser?

So then, we all know the probable outcome once this is considered by our local council; no more street theatre of this type without impossible and expensive regulations being met. And that's what's sad.


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DJE
post Jun 4 2016, 03:12 PM
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Plenty has been written elsewhere about the fun that was had by the public. And I agree it was fun.

However, it would have been simple - if the designers knew what they were doing - to ensure that the structure was safe.

It wasn't, and that was sloppy. It's not simply a matter of box ticking by an H&SE inspector. It's a matter of the people behind the project knowing what they are doing and building safety into it in the first place.

The people behind the project were demonstrably out of their depth. Fortunately it collapsed when not many people were around. That's due to luck, not to good judgement.
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Simon Kirby
post Jun 4 2016, 05:25 PM
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QUOTE (DJE @ Jun 4 2016, 04:12 PM) *
Plenty has been written elsewhere about the fun that was had by the public. And I agree it was fun.

However, it would have been simple - if the designers knew what they were doing - to ensure that the structure was safe.

It wasn't, and that was sloppy. It's not simply a matter of box ticking by an H&SE inspector. It's a matter of the people behind the project knowing what they are doing and building safety into it in the first place.

The people behind the project were demonstrably out of their depth. Fortunately it collapsed when not many people were around. That's due to luck, not to good judgement.

You may be right, but I think it's also possible that the hazard of the boxes collapsing was considered and that the likely severity was consideted to be minor - I don't know if I agree with that, but I don't entirely agree with your analysis either - I think you've over-estimated the weight of the structure. I wouldn't want to defend this if the public really were exposed to a hazard, but I don't think it necessarily follows that the structure collapsing was reckless and dangerous - though I acknowledge that's a possibility.


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DJE
post Jun 4 2016, 06:20 PM
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The structure was tethered to four water filled tanks about a metre cubed - so each weighing about ton. With the wind blowing from any particular direction, only two tons weight would be effectively holding the structure down.

To put this in perspective, a quick Google shows that a Boeing 737 has a 34m wingspan, wighs 40-70 tons and has a typical takeoff speed of about 150mph. So a 150 mph airflow across it's wings can lift 70 tons. Wind pressure blowing perpendicular to a similar wing area would be far greater.

The frontal area of the tower looks to be of a similar order of size to the wings of a 737.

It doesn't need a computer, or even a calculator, to see that in a moderate wind speed, the force on the tower would be likely to be many tons.

The tower collapsing wasn't an unlikely event, it was almost inevitable in a moderate wind. The only unkown would be whether or not it would fall on someone.

I've looked at videos of the collapse. The water tank weights don't budge, meaning the tethers either broke or came undone.

Earlier this week a boat full of refugees, being towed, got into difficulties and started to sink. Someone cut the towrope. It reportedly flew back and decapitated a woman.

A breaking tether, presumably steel, could have similar consequences.

(Edit: I suppose it is possible that the tethers were intentionally released to enable the tower to fall in a semi-controlled manner).

For those who argue that health and safety measures would kill off such art events, I would argue that appropriate measures enable art events to take place - safely.

As an engineer I dont regard H&S as an inconvenient bolt-on afterthought, but as a core element of design. It's called 'acting responsibly' - due diligence in techspeak.

One shouldn't confuse having fun with your inner (or real) child as being the same as surrendering one's safety to some incompetent who doesn't fulfil their responsibilities as a grown-up.
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On the edge
post Jun 4 2016, 08:01 PM
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QUOTE (DJE @ Jun 4 2016, 07:20 PM) *
The structure was tethered to four water filled tanks about a metre cubed - so each weighing about ton. With the wind blowing from any particular direction, only two tons weight would be effectively holding the structure down.

To put this in perspective, a quick Google shows that a Boeing 737 has a 34m wingspan, wighs 40-70 tons and has a typical takeoff speed of about 150mph. So a 150 mph airflow across it's wings can lift 70 tons. Wind pressure blowing perpendicular to a similar wing area would be far greater.

The frontal area of the tower looks to be of a similar order of size to the wings of a 737.

It doesn't need a computer, or even a calculator, to see that in a moderate wind speed, the force on the tower would be likely to be many tons.

The tower collapsing wasn't an unlikely event, it was almost inevitable in a moderate wind. The only unkown would be whether or not it would fall on someone.

I've looked at videos of the collapse. The water tank weights don't budge, meaning the tethers either broke or came undone.

Earlier this week a boat full of refugees, being towed, got into difficulties and started to sink. Someone cut the towrope. It reportedly flew back and decapitated a woman.

A breaking tether, presumably steel, could have similar consequences.

(Edit: I suppose it is possible that the tethers were intentionally released to enable the tower to fall in a semi-controlled manner).

For those who argue that health and safety measures would kill off such art events, I would argue that appropriate measures enable art events to take place - safely.

As an engineer I dont regard H&S as an inconvenient bolt-on afterthought, but as a core element of design. It's called 'acting responsibly' - due diligence in techspeak.

One shouldn't confuse having fun with your inner (or real) child as being the same as surrendering one's safety to some incompetent who doesn't fulfil their responsibilities as a grown-up.


....and did you actually voice your concerns to the organisers?

Seeing something they haven't and pointing it out at the time is what I'd term 'acting responsibility'.


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Simon Kirby
post Jun 4 2016, 10:46 PM
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QUOTE (DJE @ Jun 4 2016, 07:20 PM) *
The structure was tethered to four water filled tanks about a metre cubed - so each weighing about ton. With the wind blowing from any particular direction, only two tons weight would be effectively holding the structure down.

To put this in perspective, a quick Google shows that a Boeing 737 has a 34m wingspan, wighs 40-70 tons and has a typical takeoff speed of about 150mph. So a 150 mph airflow across it's wings can lift 70 tons. Wind pressure blowing perpendicular to a similar wing area would be far greater.

The frontal area of the tower looks to be of a similar order of size to the wings of a 737.

It doesn't need a computer, or even a calculator, to see that in a moderate wind speed, the force on the tower would be likely to be many tons.

There's some interiesting physics there.

It's atmospheric pressure that lifts an aircraft wing - as the wing moves through the air the profile of the wing causes the air to flow over the top of the wing faster than it flows under the wing, and this creates a partial vacuum on the top of the wing (the Bernoulli effect). With atmospheric pressure of 100,000 Newtons per square meter you don't need much of a partial vacuum to lift a 500,000 Newton aircraft with 100m2 of wing - it just needs 5,000 Pa of differential pressure across the wing to lift the aircraft.

Wind blowing against a surface is different, because now the pressure on the surface is created by the change in momentum of the air. Call the air density p and the wind velocity v, and then the pressure = force/area = d/dt mv/area = pv^2 - so with air density of say 1.2 kg/m^3m^3 the wind needs to be blowing at sqrt(5,000/1.2) = 65m/s which is around 150 miles per hour to create the same differential pressure that lifts a Boeing 737. But that's over simplified the argument, because the momentum isn't all given over to the surface as the wind blows around a structure.

A 10 mph wind (that's a force three, "gentle breeze") on the other hand produces a maximum pressure of 24 Pa, which is a force of 2,400 N, or the weight of 240kg over the area of a 737's wings.


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DJE
post Jun 5 2016, 07:08 AM
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QUOTE (On the edge @ Jun 4 2016, 09:01 PM) *
....and did you actually voice your concerns to the organisers?

Seeing something they haven't and pointing it out at the time is what I'd term 'acting responsibility'.

No, I saw the aftermath, and videos of the collapse.

QUOTE (Simon Kirby @ Jun 4 2016, 11:46 PM) *
There's some interiesting physics there.

It's atmospheric pressure that lifts an aircraft wing - as the wing moves through the air the profile of the wing causes the air to flow over the top of the wing faster than it flows under the wing, and this creates a partial vacuum on the top of the wing (the Bernoulli effect). With atmospheric pressure of 100,000 Newtons per square meter you don't need much of a partial vacuum to lift a 500,000 Newton aircraft with 100m2 of wing - it just needs 5,000 Pa of differential pressure across the wing to lift the aircraft.

Wind blowing against a surface is different, because now the pressure on the surface is created by the change in momentum of the air. Call the air density p and the wind velocity v, and then the pressure = force/area = d/dt mv/area = pv^2 - so with air density of say 1.2 kg/m^3m^3 the wind needs to be blowing at sqrt(5,000/1.2) = 65m/s which is around 150 miles per hour to create the same differential pressure that lifts a Boeing 737. But that's over simplified the argument, because the momentum isn't all given over to the surface as the wind blows around a structure.

A 10 mph wind (that's a force three, "gentle breeze") on the other hand produces a maximum pressure of 24 Pa, which is a force of 2,400 N, or the weight of 240kg over the area of a 737's wings.

Interesting. I'm surprised at your values for the force generated by wind.

I ultimately base my assertion that the tethering was inadequate on the rather compelling evidence that the bloody thing fell over!

Seems the artist has form, and other structures of his have also collapsed.

Another interesting point is that an area was taped off, presumably to protect the public in the event of a collapse. The tower fell across, and outside, the tape. From my experience of geometry things that are X feet high, which topple, then become X feet long. They seem to have missed this point.

Anyway, perhaps I am getting carried away and am missing the point of the work of art. It is a comment on the transience of art, of buildings, and I guess, the transience of people if they get squished.
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On the edge
post Jun 5 2016, 08:16 AM
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QUOTE (DJE @ Jun 5 2016, 08:08 AM) *
No, I saw the aftermath, and videos of the collapse........................................................
..................Anyway, perhaps I am getting carried away and am missing the point of the work of art. It is a comment on the transience of art, of buildings, and I guess, the transience of people if they get squished.


And there is a further point about the effect of news reporting on opinion which is perhaps even more interesting. As I understand it no one got hurt. Of course, it remains to be seen what happens next. Anyway, I'll probably stop going to these arty events in Newbury, too scary for me.


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