Liquid nitrogen from the Messer Group was instrumental in safely removing the danger of an unexploded second world war bomb, as part of carefully orchestrated excavation procedure carried in Germany this year.

The operation required Messer and its soil freezing technology to form a stable soil environment through which a bomb disposal team could dig down and remove the explosive device.

In December 2007, construction workers carrying out ground surveys on the site of Evonik AG in the Marl chemicals complex unearthed a 500kg aerial bomb from the
Second World War, which had to be recovered.

However, since this cluster bomb was lying underneath the foundations of a chemical production facility, it was not possible to use conventional methods for the excavation.

While it was possible to stabilise one side of the excavation with conventional measures such as sheet piling, securing the foundation side proved more difficult. Hence the involvement of liquid nitrogen from Messer.

Frozen foundations
Lances were used to inject liquid nitrogen into the ground to be frozen, withdrawing energy from the soil as well as from the water contained in it, and causing the formation of a frozen mass.

The frozen mass then formed a stable wall which also supported the load of the foundations, allowing experts to dig down to the bomb at an angle.

Within just a few weeks, everything had been installed, from the nitrogen tank to the nitrogen supply and discharge pipes, and the freezing lances to the measurement and control system.

Freezing then commenced as planned on 15th February this year. Following around 500,000kg of nitrogen pumped into the pit, the frozen mass was stable and the bomb disposal team could move in and successfully remove the device.

The frozen mass was preserved for a few more days to ensure the structural stability of the ground for the backfilling work.