The Weekly Reflektion Week 40 / 2020

Thanks to several of our readers who pointed out an error in last week’s Reflektion on tunnel safety. The Ryfylke tunnel is not the longest undersea tunnel, but the longest undersea road tunnel. There are several undersea rail tunnels that are longer, notably the Channel Tunnel. Good to see an engaged set of readers!

The partial collapse of the Ronan Point tower block in East London, UK, in 1968 is the subject of this week’s Reflektion.

Challenging existing standards may be necessary for continuous improvement, but how do we prevent economic pressure pushing limits too far?

Ronan Point was a 22-storey tower block in Canning Town, East London which partially collapsed on 16th May 1968, only two months after it had opened. Ivy Hodge, a resident in flat 90 on the 18th floor, lit a match to light the gas stove to make a cup of tea. The match sparked a gas explosion that blew out the load-bearing walls which had been supporting the four flats above. This led to the collapse of the south east corner of the building. Four people were killed and 17 injured. The investigation into the collapse led to major changes in the UK building regulations, and all nine tower blocks on the Freemason estate being demolished, along with other similar buildings around the country.

Ivy Hodge survived the incident despite being blown across the room by the explosion, as did her gas stove which she took to her new address.

The Griffiths Inquiry into the collapse found that although the design complied with the current regulations, the design was not adequate to withstand even small explosions. The fact that Ivy Hodge survived the explosion was an indication on how low the explosion overpressure was. The design was also found to be inadequate with respect to wind loading, where the assumption that all windows were closed was the basis. If the glass in a window was broken, or somebody had gone out leaving the window open, a differential pressure could be generated sufficient to cause a wall panel to fail with similar consequences as in Ronan Point. Immediately after the collapse, the government brought out an interim measure requiring all new buildings of over five storeys to be able to resist an explosive force of 34 kPa (4.9 psi).

Construction defects were also found. The building did not have adequate fire segregation , which was necessary for people to be able to survive in their flats rather than try to escape down narrow staircases. Other construction defects led to the whole weight of wall panels being supported by two steel rods in the wall panel below, instead of being evenly distributed throughout the lower wall panel. Upon demolition, the extent of the defects shocked even the activists who had been lobbying that the building was unsafe. On the lower floors, cracks in concrete floors indicated that the wholebuilding was not far from collapse.

The tower block was built using a technique known as large panel system (LPS) involving prefabricating large concrete sections offsite and bolting them together to construct the building. This was part of a period where prefabricated housing was used to give cheap affordable housing in inner city areas. Many of these blocks are still standing.

Where there is poor design and poor construction, with a focus on saving money, the results can be catastrophic. Do youallow economic pressures to degrade the robustness of the facilities and the level of safety?

Reflekt AS