NR NR/L2/ELP/27717 ISSUE 1 PDF

Applicability

This standard relates to existing bridges and similar structures (including tunnel portals) carrying a road, track or path over a railway which is, or is proposed to be, electrified using an overhead contact line system (OCLS) at 25 kV. It applies to managers and designers in any project:

a) planning new electrification, in order for them to assess what interventions will be needed to the bridge parapets for electrical safety purposes; or

b) developing designs to install new live bare conductors beneath the structure (eg conductor renewals or enhancement schemes). For renewals, the assessment should be used to prioritise future parapet interventions and should not delay like-for-like renewal.

The electrical risk assessment included in NR/L2/ELP/27717/RA applies to the parapets of bridges over the railway to be electrified in unrestricted public areas. This includes parapets adjacent to any steps, ramps or escalators leading up to such bridges, where they are within the minimum clearance distances to accessible live parts set in BS EN 50122-1 or are expected to be within such distances once the line is electrified.

NOTE 1 It is highly unusual for parapets adjacent to steps or ramps to fall within the minimum clearances set in BS EN 50122-1 other than for bridges within stations.

NOTE 2 This standard supersedes parts of NR/L3/CIV/020 and the associated Variation Pending Standards Change reference TR70250. NR/L3/CIV/020 will be modified accordingly. 

Exclusions

This standard does not apply to new bridges, ie where the bridge itself is subject to authorisation under the Railways (Interoperability) Regulations 2011. 

This standard does not apply to bridges to which the public does not have unrestricted access, e.g signal gantries or bridges restricted to railway staff use only.

Where the vertical distance from the standing surface on the bridge to the highest live conductor is more than 3.1 m, BS EN 50122-1 does not require any further mitigation. Hence this standard does not apply in such circumstances. 

Figure 1 shows the minimum clearance distances from live equipment defined in BS EN 50122-1. If all distances are met, the location is not in scope of this standard.

Bridge parapets also mitigate the risks of a person falling or throwing something from the bridge, but these risks apply equally to non-electrified lines so are not considered here. Further requirements for alterations to bridge parapets are given in NR/L3/CIV/020 and a full risk assessment of the railway boundary is set out in NR/L2/OTK/5100. A full risk assessment could result in the overall risk being considered greater than the electrical risk, and therefore additional mitigation measures being required beyond those specified in this standard.

Purpose 

This standard concerns the parapet arrangements for a bridge over a railway that is, or is to be, electrified using an overhead system. The risk to be mitigated is of a deliberate (mischievous) or accidental act where someone on the bridge holds a long object over the parapet, and the object comes into contact with an electrically live component (or so close to it that an arc forms between the object and the live component). This could seriously injure or kill the person holding the object. Deliberate acts intended as suicide attempts are not considered. 

The standard sets out an agreed process for assessing the electrical risk at a specific bridge. This enables electrification projects to select the appropriate mitigations that will need to be installed at the bridge prior to energisation. The assessment therefore leads to an improvement in safety where needed, while avoiding unnecessary costs in installing mitigations where they are not proportionate to the risk.