Fault Tree Points

[PJW]

Hi,
I want to attempt the fault tree for Points. I request you to guide me to do that as the way you helped for DC Track Circuits in the below thread:

http://www.irseexam.co.uk/showthread.php?tid=294.

Please help.

First think about what "points failure" means. You ought to be able to list a number of different "top events"- diverse ways in which a set of points might adversely affect the efficient and safe operation of the railway. Some may cause delay or prevent the passage of traffic altogether, others may be immediately and directly dangerous, others perhaps a latent fault which lies dormant for a while before having its adverse effect. In doing this you are looking "top down" by regarding "points" as components within the entire railway system.

Then think about all the things that could go wrong and compile yourself a list of faults.
a) Think about the whole range of component parts: mechanical, electrical, signalling, P'Way, power, within the mechanism itself and all its related support equipment and interconnections.
b) Also think about the manner in which they go wrong: normal physical wear, deterioration due to age, chemical attack, abnormal loading, mechanical shock, vibration, electrical overload, extremes of weather, user abuse, vandalism .......
In doing this you are looking "bottom up" by regarding "points" as a system composed of smaller components.

So try to pair things up in typical combinations that displays your knowledge of point mechanisms and of failure modes:
part a may seize up (why?)
part b may loosen (why?)
part c may leak (why?)
part d may become detached (why?)
part e may burn out (why?)
part f may fracture (why?)
part g may become out of alignment (why?)
..................................................
something external x may obstruct (why?)
something external y may cause physical damage (why?)
someone z may do something careless (why?)

Now what you now need to do is to consider what faults in what combination and in what circumstances conspire to create the various top level events which you identified initially.

Connect up in a logical manner using AND / OR gates to combine the various threads suitable, then job done.
Simples.

So have a go and submit your efforts.
Use the example for a signal in the GM Rail event thread as an example from which to work.

[Jerry1237]

Firstly, define what you mean by points. The signalling scope for points is generally reasonably well defined in the UK but differs across countries and even infrastructure owners!

Care is needed when stating what constitutes a failure. For example, a detection switch can gradually drift out of tolerance and for the operator, that is a failure. However, for signalling, it is a design feature and the system is working correctly. In reverse, the frog could fracture but the signalling system wouldn't indicate the mechanical failure, the operator may not detect it either but the PWay techs would classify it as a failure.

Jerry

[PJW]

Firstly, define what you mean by points.

Jerry

Before anyone says that Jerry is taking too much of a module 1/7 view, do reflect on the 2007 module 5 question:

For a top event of your choice, prepare a fault tree for a set of power operated points including the switch and stock rails, identifying the most probable cause of the top event.
[15 marks]
Describe the precautions to be taken to protect against this top event.
[5 marks]

[PJW]

Firstly, define what you mean by points.

Jerry

Before anyone says that Jerry is taking too much of a module 1/7 view, do reflect on the 2007 module 5 question:

For a top event of your choice, prepare a fault tree for a set of power operated points including the switch and stock rails, identifying the most probable cause of the top event.
[15 marks]
Describe the precautions to be taken to protect against this top event.
[5 marks]


However do READ carefully; in 2004 the question clearly focussed on the signalling element but not exclusively the on track equipment:

Draw a fault tree for a point machine of a type you are familiar with. Include in your answer the machine and all its components, the mechanical connections to the track, the cables between the machine and its controlling apparatus, and the detection relays.

Also see this thread