โ Guidance
TC failure classifications
High / Low / Negligible per NR/L3/SIG/10047 Mod 03 โ determines FMS risk level, response and sign-back requirements.
High
- SCWO โ automatic signal
- SCWO โ signal working in auto / ARS
- SCWO โ controlled signal
- SCWO โ level crossing (except ABCL/AOCL/TMO with driver's indicator)
- Showing clear with TC interrupter broken
- TCOD โ occupied circuit clearing after correct TCOD
- USR not timed out (poster only โ Appendix I rates this Low; see footnote)
Low
- Indication-only circuits
- ABCL/AOCL/TMO crossings only
- Drop shunt >0.2ฮฉ below minimum
Negligible
- Under 300ms
- <1s striking in/out with abutting circuit occupied
- After protection (special block) in place
- Rusty rails โ TS11
- Sequencing controls effective
Hazard index
| Failure mode | RIDDOR | Hazard | Rating | Class |
|---|---|---|---|---|
| SCWO โ automatic signal | Yes | Potential unsafe wrong-side condition (false clear) | H9 | High |
| SCWO โ signal working in auto / ARS | Yes | Potential unsafe wrong-side condition (false clear) | H7 | High |
| SCWO โ controlled signal not in auto | Yes | Potential unsafe wrong-side condition (false clear) | H6 | High |
| Showing clear with TC interrupter broken | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| TCOD โ occupied circuit clearing after a correct TCOD | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| SCWO โ controlling a level crossing (except ABCL/AOCL/TMO) | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| SCWO โ route locking maintained, USR not timed out | No | Limited / protected wrong-side condition | L2 | Low |
| SCWO โ ABCL/AOCL/TMO crossing only | No | Limited / protected wrong-side condition | L2 | Low |
| Drop shunt โฅ0.2ฮฉ below minimum | No | Limited / protected wrong-side condition | L2 | Low |
| SCWO โ indication-only circuit | No | Limited / protected wrong-side condition | L1 | Low |
| SCWO โ under 300ms | No | No credible hazard | N0 | Negligible |
| SCWO โ sequencing controls effective (SSI8003-82) | No | No credible hazard | N0 | Negligible |
| SCWO โ <1s striking out/in at TC boundary with abutting circuit occupied | No | No credible hazard | N0 | Negligible |
| SCWO โ after TS11 special block imposed | No | No credible hazard | N0 | Negligible |
| Rusty rails โ TS11 arrangements | No | No credible hazard | N0 | Negligible |
Classification per NR/L3/SIG/10047 Mod 03 ยง10.1. High classifications are RIDDOR-reportable; RIDDOR and S&TINCS referencing follows the same module.
Discrepancy: the 'Classifications of TC failures' poster shows 'SCWO โ route locking maintained, USR not timed out' as HIGH, whereas Appendix I rates it LOW (L2). Resolve with route S&T before relying on either โ treat as the higher classification until confirmed.