Safety Bulletin NRB21-10 - Flame cutting or welding in tunnels

    Safety Bulletin NRB21-10 – Flame cutting or welding in tunnels


    A team of contractors working for Capital Delivery went into Sevenoaks tunnel intending to use oxypropane cutting equipment to cut some metal work out of one of the ventilation shafts.

    A welding team from maintenance told the contractor team they could not use propane in the tunnel.

    The oxypropane equipment was removed.

    The contractors were cutting at a high level in and around the ventilation shaft in the tunnel.

    The contractor had assessed the risks and identified that a leak or release of acetylene, an alternative fuel gas that is lighter than air, may collect in the vicinity.

    Application of a flame may then ignite it.

    For that reason, the work planning had rejected the use of acetylene and chose propane as a safer alternative for this specific task.

    Network Rail’s company standard for welding the track (i.e. at ground level) only recognises use of acetylene because propane could gather at a low level creating a fire or explosion risk.

    An investigation is underway and there is a planned review of fire prevention/precautions in the company standards for cutting and welding in tunnels.


  • Using any flammable gases in tunnels or ventilation shafts involves increased risk and alternative methods should always be considered.
  • All confined space welding or cutting tasks that plan to involve either propane or acetylene must be thoroughly risk assessed in advance.
  • Appropriate control measures should be recorded in the risk assessment and used on site.
  • The two fuel gases have different properties:

  • Acetylene is lighter than air so any leaks will rise, including up ventilation shafts.
  • Propane is heavier, so any leaks will gather at low level, including possibly in drains.
  • Using acetylene involves specific hazards in the event of a fire and requirements for how cylinders must be handled.
  • Whichever gas is selected, equipment must be checked to prevent leaks and the amount of cylinders in the confined space kept to a minimum.
  • Accurate information about the location and amount of fuel gases should be readily available to the emergency services if an incident does occur.
  • Are you aware of the ‘work safe’ procedure and how to raise one?
  • How can you help people feel empowered to stop work if they came across unsafe activity or behaviour?