More on electrical clearances
My heavily technical analysis of overhead line electrical clearances in last months column had informed observations whizzing into my e-mail in-box. The European Railway Agency send a surprisingly supportive letter. ORR also provided a policy statement and Network Rail sent me a chapter and verse and paragraph and sub-paragraph - guide to the respective regulations.
Last months item focused on clearances to structures. This month its the turn of clearances from parts of 25kV electrification systems to standing surfaces to which members of the public may foreseeably gain access.
No room for detail here save to highlight BS EN 50122-1, the standard dealing with protective provisions against electric shock. Previously this took the UK loading gauge into account, with a UK specific case establishing an electrical clearance of 2.75m as a minimum. The revision in 2011 removed this special UK condition and today the use of any clearance under 3.5m must be justified by risk assessment.
ORR points out that no other industry uses a dimension as low as 3.5m to achieve compliance with the Electricity at Work Regulations for 25kV systems, so its use already takes into account the constraints of UK rail infrastructure. As such, the scope for further compromise of this already significantly reduced clearance distance without accompanying mitigations is extremely limited.
In response to this policy statement I fired off an e-mail to ORR asking five questions, concerning risks and real world data, such as the number of passengers at stations electrocuted by 25kV overhead lines or rolling stock pantographs. ORRs ever helpful press office arranged an phone conference with their relevant expert. After the hellos, I was told that they couldnt answer the questions and an embarrassing, if informative discussion ensued. More dead parrot stuff.
Back in April ORR had written to Network Rail following a meeting to discuss how its legal duties in relation to public safety from new overhead line equipment at stations can be met. According to the letter all Network Rail has to do is produce high-quality site-specific risk assessments, demonstrating that all that is reasonably practicable to protect the public and staff is being done.
Site specific note. Think of the engineering hours this will take up. No wonder in Scotland Phil Verster gave up the fight for common sense and told his team just do what they want or well never get the wires up. According to ORR, addressing and recording the specific conditions at each location will provide greater transparency than a mechanistic, number-based risk assessment process. Its only time and money.
Network Rail took me through the regulations in detail. The elimination of the Reduced Minimum (200mm) and Special Reduced (150mm) structure clearances from the standard, leaving only the Normal structural clearance of 270mm, is seen as a good thing. Since there is no longer a minimum clearance specified, the relevant clause actually relaxes the previous Group Standard. I suppose the theory is that each bridge can have a customised clearance, say 131.5mm if you can get it past ORR.
On platform clearances, Network Rail supplied some wonderful examples of the regulation writers art. In the Committee responsible Network Rail obtained a relaxation to the relevant requirement to reflect the restricted GB gauge. This allowed RSSB to publish a GB specific requirement for platform clearances in our old friend GL/RT1210.
When all this was reviewed by the relevant British Standards committee it was agreed that, while the previous 2.75m clearance was not justifiable as a minimum limit in a standard, it might be justifiable subject to a risk assessment. So, according to Network Rail, electrical clearances below 3.5m are possible with risk assessment.
Whats really infuriating about this safety-by-diktat, is that the engineers concerned know that it is irrational and yet they go along with it. To paraphrase Edmund Burke, the only thing necessary for the triumph of bureaucracy over common sense is that good engineers should do nothing.
