From an initial route trace and survey, that led to a backdrop outlet in an extremely deep, 2 landing and off-set chamber, our client requested that we fully trace and CCTV condition survey to the outfall.

Though surface water only, at almost 12m underground (5m to the 1st level and 7m to the outfall pipe’s inlet) and the access to the 2nd landing off set by around 4m it was time for some serious planning on how we could achieve this minor surveying miracle.

Our initial (standard) confined space entry had given outline information and we understood:

– There were no overt concerns with gasses and the initial chamber was large enough as to not cause a CO2 build up with multiple entrants
– The outlet pipe was going to be at least 225mm, therefore our Minicam CRP140 Crawler CCTV would be right for the project
– We would need to have 4 suitably qualified (high risk confined space entry) and 3 entrants (1 becoming a 2nd top ‘man’)
– Atmosphere monitoring would need to be conducted before entry, constantly at the first level entry (suspended and personal gas monitors) and a 2nd suspended monitor at the 2nd ladder point before the final entrant could descend (with their own personal monitor); 5x gas monitors therefore used

We would need to utilise 2x Tripod and fall arrest/rescue winch system; one set up the initial entry and the 2nd set-up at the 7m descent point and associated equipment:

– 4x rescue harnesses would be required
– 2x 15m safety lines would be used to allow for traceable movement for 2 entrants during the work
– 3x 15-minute escape sets would be lowered and donned by each entrant
– The entire works would need a good level of illumination (in this instance provided by 2 of the excellent Milwaukee Tool M18AL-0 18v Trueview Rover Area Lights – there was no requirement for intrinsically safe equipment for this operation)
– All members of the team would be fully briefed of the method and actions in an emergency situation, with carefully considered Risk Assessment / Method Statement and dynamic Point of Works Risk Assessments (completed just prior to entry)
– We would notify the local fire & rescue services of our project before (with specific details), at the point of entry and once all had safely exited, with our entry permit closed

A full survey was gained to 44m to the outfall; this last piece of footage will be added to our current information to complete the client’s full WinCan report.

What an amazing structure and piece of engineering!

Conducted by high risk CSE trained and certified operatives, the Arrowflow team have again safely, efficiently and successfully completed another challenging survey project.