RAI/Track Safety/TBT-RAI-008

COSS (Controller of Site Safety) Role

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COSS (Controller of Site Safety) Role

Toolbox Talk Record

Ref: TBT-RAI-008  |  Issue: 1  |  Date: March 2026
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What?

  • The COSS is the person responsible for implementing the safe system of work on or near the railway.
  • They control the safety of a worksite, ensuring all workers are protected from train movements.
  • A COSS must hold a valid PTS card and the COSS competency, verified through the Sentinel system.
  • The COSS briefs all workers before they go on or near the line, covering the safe system in use.
  • Safe systems include lookout warning, separated protection, possession, and line blockage arrangements.
  • The COSS must establish the limits of the worksite and ensure everyone remains within the safe zone.
  • They are responsible for warning workers and ensuring everyone moves to a position of safety when required.
  • A COSS cannot also act as a lookout; these must be separate people with separate duties.
  • Before work begins, the COSS must confirm the safe system is in place and brief all personnel.
  • Network Rail standards and the Rule Book govern all COSS duties and responsibilities on the railway.

Why?

Prevent train strikesWorkers struck by trains on the railway suffer fatal injuries. The COSS is the front line of defence against this risk.
Legal and regulatoryNetwork Rail standards mandate that a competent COSS controls every worksite on or near the running line.
Clear accountabilityThe COSS role ensures one named person is accountable for the safety of every worker at the site.
Do Don't
  • Confirm your COSS competency and Sentinel card are valid before each shift.
  • Brief every worker on the safe system of work before going on track.
  • Establish and clearly mark the limits of the safe zone before work starts.
  • Maintain awareness of train movements and approach times at all times.
  • Ensure a separate lookout is appointed where lookout warning is the safe system.
  • Conduct a site-specific risk assessment before implementing the safe system.
  • Account for every person entering and leaving the worksite throughout the shift.
  • Give clear, timely warnings so all workers reach safety before a train passes.
  • Stop work immediately if the safe system is compromised for any reason.
  • Record the safe system details and briefing attendance for each work period.
  • DON'T act as both COSS and lookout simultaneously; these are separate roles.
  • DON'T allow anyone on or near the track without a valid PTS card.
  • DON'T permit work to start until the safe system briefing is complete.
  • DON'T exceed the agreed worksite limits defined in the safe system.
  • DON'T allow distractions to compromise your awareness of train movements.
  • DON'T continue work if the safe system of work has been breached.
  • DON'T assume the line is blocked without confirmation from the signaller.
  • DON'T leave the worksite without ensuring all personnel are accounted for.
  • DON'T let workers return to the track after a warning until it is safe.
  • DON'T take on more workers than you can safely control and warn.

See also: Rail Safety Awareness | Safe System of Work on Track
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