I was amazed at the statement that under RIDDOR, 5t of material needed to fall before a structural collapse was reportable (Hole in live Thameslink tunnel 'not serious enough' for probe - HSE, NCE 17/24 April).
Since my main occupation as chief engineer to a precast cladding company is to ensure that panels 'stay put' on a building, I checked the regulations for myself, out of professional curiosity.
Schedule 2, Part I, clause 18a does indeed refer to 'Any unintended collapse or partial collapse of any building or structure (whether above or below ground) under construction, reconstruction, alteration or demolition, which involves a fall of more than five tonnes of material'.
However the crucial aspect is that the tunnel itself was not 'under construction, reconstruction, alteration or demolition', thus the clause is not relevant anyway.
Further reading led me to Part IV, clause 70, which relates to 'Accidents involving failure of the works on or connected with a relevant transport system'.
Specifically it goes on to list 'The following classes of accident where they are likely either to cause an accident to a train or to endanger any person lthe failure of a tunnel, bridge, viaduct, culvert, station, or other structure or any part thereofà' lthe striking of a bridgeàby a road vehicle or its loadà' I would think the excavator struck the tunnel a great number of times! I cannot believe that the incident was not serious enough for an investigation, and wonder whether we are getting the full story.
Cliff Billington (M), 2 Fountains Close, West Bridgford, Nottingham NG2 6LL