Is too much safety stuff dangerous?

[AndrewE]

Track equipment consists of a permanent magnet with South pole uppermost to act as a marker and initiate AWS action (a dead magnet on its own can't do anything as there is no field to influence the receiver).
The following electro-magnet presents a North pole when energised. South resets the 'sunflower' to 'all black'. If followed by North within a certain time the bell sounds....

To follow on from this, apparently AWS equipment was sold to Australia where it was found not to work very well... an academic consultant (scientist rather than engineer) was sent to work out why, and came up with the answer that AWS was designed to work in "our" northern hemisphere, but in the southern hemisphere the earth's magnetic field was opposing it rather than assisting it. The solution was to reverse the polarities for use out there!

 

[HaggisBotherer]

To follow on from this, apparently AWS equipment was sold to Australia where it was found not to work very well... an academic consultant (scientist rather than engineer) was sent to work out why, and came up with the answer that AWS was designed to work in "our" northern hemisphere, but in the southern hemisphere the earth's magnetic field was opposing it rather than assisting it. The solution was to reverse the polarities for use out there!

Hmmm... sounds suspiciously like the urban myths that water spirals out of a sink the opposite way in the southern hemisphere and that Australia is upside down

Mildly amused to note that, four pages and 107 posts on, in reality the thread is no further on from...

This thread in a nutshell:
Is safety equipment actually dangerous? No
Is human error dangerous? Yes.

 

[edwin_m]

aws at least 30 years ago
was a reciever on the train with a rocker 'dead magnet rocks one way live magnet rocks back and cancels operation as does the cancel button in cab
there are no connections to any electrical systems what so ever [appart from the cab cancel button]so a dead system fully operated by the track magnet air pressure and venting the brakes to atmosphere by direct valve action
later ones where more "electrical " when retro fitted to emus for example but no more than for powering there action and not for intelligent interaction with systems

How did the original ones get power to work the bell and the sunfllower? I've heard of "AWS battery boxes" being fitted to steam locos so I suspect even the original versions of AWS needed power (unlike GWR ATC).

The original receiver was, as you say, a magnetically biased two position contact which would 'tip' over centre under the influence of the field. This type wasn't fast acting enough for HSTs, which had an alternative design using reed switches.

When I was involved around 1994 in the project that eventually led to TPWS, the reed switches were the standard fitment but some component (possibly the switch itself) was obsolete. TPWS was designed to replace the AWS euipment, using the same fixings and train interface to make installation easy, and also replicated the AWS functionality using (I think) a Hall Effect sensor instead of the reed switches.

 

[AndrewE]

Hmmm... sounds suspiciously like the urban myths that water spirals out of a sink the opposite way in the southern hemisphere and that Australia is upside down

... apart from the two facts that the magnetic field is different down under (try reading the Wikipedia page https://en.wikipedia.org/wiki/Earth's_magnetic_field)

In the northern hemisphere, the field points downwards. It is straight down at the North Magnetic Pole and rotates upwards as the latitude decreases until it is horizontal (0°) at the magnetic equator. It continues to rotate upwards until it is straight up at the South Magnetic Pole

and it was a BR S&T workshop manager (i.e. head, not supervisor) who told me: His shops refurbished AWS equipment for a living, including stripping all components down to bare metal before refinishing them and rebuilding.

 

[big all]

yes the bell and sunflower are electrical as will other parts be its more the point that none off the other warning systems operate in conjunction with or effect the aws operation just the track magnet and driver canceling the horn

 

[Strat-tastic]

Hmmm... sounds suspiciously like the urban myths that water spirals out of a sink the opposite way in the southern hemisphere...

It really does y'know
Centripetal force

 

[Peter Mugridge]

It really does y'know
Centripetal force

Sorry, but in my house the vortex for the basin plughole spins one way and that for the bath plughole, three feet away, spins in the opposite direction... I don't think the equator runs through the middle of my bathroom.


Getting back on topic - it's not the extra safety stuff in itself which is dangerous but the attitude of complacency which some people develop as a result of all the safety stuff. For example people who think that cruise control on a car is the same as autopilot in an aircraft. It isn't. Most people know that. Some don't. It's those few people who cause the hazard. Same with other safety stuff. If it's used properly, it does what it's intended to do. If an idiot thinks it'll protect them if they let it do everything - it won't.

 

[Strat-tastic]

Sorry, but in my house the vortex for the basin plughole spins one way and that for the bath plughole, three feet away, spins in the opposite direction... I don't think the equator runs through the middle of my bathroom.

No, it really does.

Imagine looking at planet earth from above the North pole. Now place a bowl of water on it. After some time of the bowl rotating with the earth, the water naturally gathers rotation in the same direction as the bowl. Note the direction of spin.

Now look at it from underneath, which is the equivalent of an identical bowl at the South pole. The spin is now in the opposite direction.

As for your situation, maybe your sink, say, has such a configuration of taps that the force of water coming out creates a spin in the opposite direction to what you get in the Northern hemisphere. I'd suggest that if you left the sink for an hour or two for the unnatural spin to slow and reverse, you'd see both sink and bath spin in the same directions when emptying.

 

[tsr]

No, it really does.

Imagine looking at planet earth from above the North pole. Now place a bowl of water on it. After some time of the bowl rotating with the earth, the water naturally gathers rotation in the same direction as the bowl. Note the direction of spin.

Now look at it from underneath, which is the equivalent of an identical bowl at the South pole. The spin is now in the opposite direction.

As for your situation, maybe your sink, say, has such a configuration of taps that the force of water coming out creates a spin in the opposite direction to what you get in the Northern hemisphere. I'd suggest that if you left the sink for an hour or two for the unnatural spin to slow and reverse, you'd see both sink and bath spin in the same directions when emptying.

This only works for relatively large bodies of water (where the phenomenon is usually clearly visible), such as pipework associated with large reservoirs. Anything on the scale of a bath or sink will not reliably demonstrate this effect.

Anyway, back to the trains...

 

[AndrewE]

Hmmm... sounds suspiciously like the urban myths that water spirals out of a sink the opposite way in the southern hemisphere and that Australia is upside down

It's interesting how a challenge stimulates the grey matter.... I now recall more of the story:
In the UK the AWS permanent magnet (assisted by the earth's magnetic field, and part of a system that was developed here, remember) gives the first prompt, which might then be cancelled by the reverse-polarity electromagnet.
In the antipodes the UK-spec permanent magnet (the supposedly fail-safe part of the system) was opposed by the the earth's magnetic field and therefore was to weak to initiate the AWS prompt, so the electromagnet had nothing to do, i.e it was irrelevant. A big fail-to danger situation - that was sorted out quite quickly, however.

 

[whhistle]

If AWS was eradicated overnight, I'm sure we'd enjoy discussing the modern day 'Southalls' and 'Harrows' and 'Eccles' on this forum.

Or would it help drivers become much more careful when driving?

That is... until they become lazy and stop noticing the different signals.
I become lazy when driving in that I can drive from A to B without really concentrating - the official term is "Highway Hypnosis".

 

[PeterC]

Or would it help drivers become much more careful when driving?

That is... until they become lazy and stop noticing the different signals.
I become lazy when driving in that I can drive from A to B without really concentrating - the official term is "Highway Hypnosis".

Easy to go onto auto pilot and take a turning that you are accustomed to taking rather than the one you need to take. I have certainly found myself going the wrong way round the M25 on one occasion. Maybe the Japanese have something when they require train drivers to actually call out each signal that they see

As I commented earlier, in most cases a certain amount of operator complacency means that safety devices never achieve their full potential. That may mean that the improvement is just 95% instead of 100%.

 

[Strat-tastic]

This only works for relatively large bodies of water (where the phenomenon is usually clearly visible), such as pipework associated with large reservoirs. Anything on the scale of a bath or sink will not reliably demonstrate this effect.

Forgive me if I'm straying, but there is a clear point of physics which needs to be made, at least as I understood it from my uni days.

I see what you're saying about large bodies of water, but even a tiny amount of angular momentum gained at the outer edge of a basin, once drawn into the centre to go down the plug, the rpm increases dramatically. Compare a ballerina spinning with arms outstretched then the rpm increases when she draws her arms in.

Anyway, it's what I was taught from a learned lecturer and I'm sticking to it

 

[quantinghome]

Risk compensation is a real effect, and applies where there is a real perception of increased safety, but it is unlikely that risk compensation will totally override a safety benefit all the time.

With motorists, it is not just the safety of the driver and passengers that matters, it is the safety of non-occupants, in particular vulnerable road users. The risk associated with motoring are largely externalised on pedestrians and cyclists, and if a greater feeling of safety results in drivers compensating by taking more risks, that will manifest itself in an increase in risk for vulnerable road users, which won't be visible looking at all road KSI numbers.

Change in fatalities over the past 40 years break down shown below. The reduction is fairly consistent over all road user groups; the only major reversal is motorcyclists from 1996 to 2003. It could be suggested that vulnerable groups have modified their behaviour (e.g. fewer children playing in the street) but would be tricky to back up with hard evidence rather than anecdotals.

 

[Dieseldriver]

Or would it help drivers become much more careful when driving?

That is... until they become lazy and stop noticing the different signals.
I become lazy when driving in that I can drive from A to B without really concentrating - the official term is "Highway Hypnosis".

Well no. I mean literally there are statistics that show a reduction in collisions caused by SPADs since widespread fitment of AWS and a further reduction since widespread fitment of AWS...

 

[edwin_m]

Forgive me if I'm straying, but there is a clear point of physics which needs to be made, at least as I understood it from my uni days.

I see what you're saying about large bodies of water, but even a tiny amount of angular momentum gained at the outer edge of a basin, once drawn into the centre to go down the plug, the rpm increases dramatically. Compare a ballerina spinning with arms outstretched then the rpm increases when she draws her arms in.

Anyway, it's what I was taught from a learned lecturer and I'm sticking to it

That may be so but there are probably many other things to do with the shape of the vessel, even which tap the water came from probably sets it swirling very slightly one way or the other. I can't think the rotation of the earth makes any difference unless all these other effects are precisely equal. The poster further back with a basin and a bath in the same room draining in opposite directions makes the point better than I can.

 

[Strat-tastic]

That may be so but there are probably many other things to do with the shape of the vessel, even which tap the water came from probably sets it swirling very slightly one way or the other. I can't think the rotation of the earth makes any difference unless all these other effects are precisely equal. The poster further back with a basin and a bath in the same room draining in opposite directions makes the point better than I can.

As I say, leave it an hour or two for the natural rotation to assert itself.

 

[The Crab]

I think there might be a little confusion between pulling the plug on a basin of still water and observing what happens when the tap is running.

 

[edwin_m]

I think there might be a little confusion between pulling the plug on a basin of still water and observing what happens when the tap is running.

Even if the tap is turned off the water may still be circulating for some time. It may not be fast enough to be visible but it could be fast enough to counteract the rotation of the earth (=once per day...).

 

[Richard Ingram]

The Coriolis effect would cause water to drain in different directions, all else being exactly balanced, but on the scale of a bathtub, other effects will likely dominate. There is a good video on youtube about this.

Equally, I find it unlikely that the Earth's magnetic field in Australia would cause too much of a problem with AWS. Looking on Wikipedia (I know, if someone has a better source, I'll stand corrected), the Earth's magnetic field at the surface varies from 25 to 65 microteslas, while the standard strength AWS magnets are 2 milliteslas(measured 5 in above, which I assume is the distance to the switches on the train), or 30-80 times greater. If a 3% difference in signal is enough to cause problems, I would say the magnets need to be stronger everywhere. Apparently they are stronger in DC third rail areas because the live rail produces interference. I would also assume that during installation and testing the field strength in situ is measured, and so the Earth's magnetic field would be taken into account at that point.
That being said, there is no reason not the swap them around so the fail-safe position is the one augmented.

As to whether safety equipment is actually dangerous, I would say the answer is sometimes. An airbag in a car can cause injury in multiple ways, and can be lethal to a child in a rear facing seat. All safety equipment must be used carefully and appropriately. If too many false positives cause the driver to automatically reset the safety system, and thus miss the one time it matters, that is an issue, and research should be done and changes made. But the rates that this occurs should be compared to the rates of errors that happen without the system. I would guess that the errors it prevents massively outnumber any errors that wouldn't have occurred had the system not been in place. The study of risk, risk understanding and risk mitigation is an interesting topic.

 

[AndrewE]

Equally, I find it unlikely that the Earth's magnetic field in Australia would cause too much of a problem with AWS. Looking on Wikipedia (I know, if someone has a better source, I'll stand corrected), the Earth's magnetic field at the surface varies from 25 to 65 microteslas, while the standard strength AWS magnets are 2 milliteslas (measured 5 in above, which I assume is the distance to the switches on the train), or 30-80 times greater. If a 3% difference in signal is enough to cause problems, I would say the magnets need to be stronger everywhere. Apparently they are stronger in DC third rail areas because the live rail produces interference. I would also assume that during installation and testing the field strength in situ is measured, and so the Earth's magnetic field would be taken into account at that point.
That being said, there is no reason not the swap them around so the fail-safe position is the one augmented.

If you let me know when you are in the north midlands I will arrange a meeting and you can call my informant a liar to his face: I would not do it. It will be an interesting encounter to watch...

 

[Richard Ingram]

I never called anyone a liar, if better numbers can be found I am happy to be wrong, but these types of stories spread very easily, as the discussions above about the sink draining proves, and your post says that your friend heard it at least second hand. I am sure there could be any number of ways the story started, maybe some misunderstanding about localised magnetic geology. Or it might be true, and I have missed something, I have some idea about magnetism and geophysics since I studied them at uni, but I am not an expert in either area. My calculations were merely a quick comparison of the scale of the forces involved, and I think that if the story is true, I would need more compelling evidence than hearsay. If the numbers had come up differently, I would just have said 'ha', and filed it away along with the sort of interesting facts you get from QI.

 

[Dieseldriver]

If you let me know when you are in the north midlands I will arrange a meeting and you can call my informant a liar to his face: I would not do it. It will be an interesting encounter to watch...

Your mate sounds well hard

 

[whhistle]

Maybe the Japanese have something when they require train drivers to actually call out each signal that they see.

There's a Wikepedia article on it... https://en.wikipedia.org/wiki/Pointing_and_calling

Yet in some parts of the word, pointing is considered rude!

 

[Panupreset]

Change in fatalities over the past 40 years break down shown below. The reduction is fairly consistent over all road user groups; the only major reversal is motorcyclists from 1996 to 2003. It could be suggested that vulnerable groups have modified their behaviour (e.g. fewer children playing in the street) but would be tricky to back up with hard evidence rather than anecdotals.

View attachment 59623

What do we notice has happened on the graph for about the last ten years?
The same thing that has happened to safety levels in many systems and organisations. Safety levels have platued and further improvement is not being made.

 

[axlecounter]

Because we’re so low that you can’t get lower? Just asking.

 

[Panupreset]

Because we’re so low that you can’t get lower? Just asking.

Not with traditional approaches to safety.

 

[Ken H]

Sorry, but in my house the vortex for the basin plughole spins one way and that for the bath plughole, three feet away, spins in the opposite direction... I don't think the equator runs through the middle of my bathroom.


Getting back on topic - it's not the extra safety stuff in itself which is dangerous but the attitude of complacency which some people develop as a result of all the safety stuff. For example people who think that cruise control on a car is the same as autopilot in an aircraft. It isn't. Most people know that. Some don't. It's those few people who cause the hazard. Same with other safety stuff. If it's used properly, it does what it's intended to do. If an idiot thinks it'll protect them if they let it do everything - it won't.

which is what i was sort of saying in the OP.

 

[Ken H]

Or would it help drivers become much more careful when driving?

That is... until they become lazy and stop noticing the different signals.
I become lazy when driving in that I can drive from A to B without really concentrating - the official term is "Highway Hypnosis".

the scary thing which we all have done is when you finish a journey and you cant remember any of it.
I bet train drivers get that too.
Humans can do quite a lot on auto-pilot, but are we alert enough when the **** hits the fan?

 

[Ken H]

There's a Wikepedia article on it... https://en.wikipedia.org/wiki/Pointing_and_calling

Yet in some parts of the word, pointing is considered rude!

The advanced motoring people say giving a commentary when driving on the road makes you more aware of stuff outside. Maybe the japanese do this for the same reason?