millemille
Member
- Joined
- 28 Jul 2011
- Messages
- 353
This is a well known fault in networkers. You can get interlock with a door obstructed. Happened at Huntingdon and kings cross as well. If you try to open the doors after the driver presses 'close doors' nothing happens. If you try a second time within a couple of seconds the door will open but no hustle alarm sounds and it immediately closes again which it appears is what happened here. Then when you become trapped the rubber seal strips on the doors closes around various obstructions (such as hands and coats and now apparently bags) and seals them firmly into the doors. The driver gets interlock and the train is able to take power.
I take issue with your use of the term "fault".
There is no fault with Networker doors in relation to the Huntingdon and other similar accidents, I say that having spent 20+ years building, commisioning, modifying, supporting and maintaining all EMU Networkers.
The doors of the 365/465/466 units are fully compliant with the regulations that were in place at the time of the relevant design certification. The regulations that are in place now are more rigourous with regards to obstacle detection and withdrawing forces but are not retrospectively applied.
The issue is not, as you suggest, that you obtain interlock with the door obstructed. The door is not obstructed - 1st and 2nd stage interlock is achieved and the active locks are engaged because the door leaves have gone fully home to the closed position with items less than the mininum obs detection triggering thickness - coats, fingers, bag straps etc - trapped in the door leading edge rubbers.
This would be the same for most current powered door designs, even with door rubbers having leading edge obs detection.
The issue is around the withdrawing forces required to extract the trapped items.
The Networker leading edge rubbers dove-tail into each other and once the locks on the leaves are enagaged it is very difficult to extract any trapped fabrice/material unless considerable force, well in excess of current RGS requirements, is exerted.
In the aftermath of Hunntingdon I personally carried out extraction force testing with engineers from FCC and HSBC using a variety of materials and a variety of door air operating pressures to investigate possible simple solutions.
The conclusion is without a complete redesign of the of the door rubbers and leaves it isn't possible to reduce the withdrawing forces to meet current RGS requirments and when you consider the costs of such a modification (and it wouldn't be this modification in isolation because as soon as you embark on such a modification any associated change with the modification all have to
be compliant with current RGS requirements) vs. the consequence it just doesn't make sense to carry out any modification.
Thousands of DOO despatches are made safely every day on the Networker fleets and the MTBF does not warrant modification.
I await the RAIB's report with interets to find out whether, as in every previous entrapment accident involving Networker units, the trapped MOP/passenger either ignored the hustle alarms of actively interfered with the operation of the doors.