Remediation: pyrotechnic risk under control at the former refinery

The pyrotechnic hazard was well known. BAck in June 1944, in this small coastal town in the Hérault region, an American bombardment had wiped out the oil installations as well as much of the town center, only a few hundred meters away. In 2018, well before the start of remediation works, a Historical and Technical Study of Pyrotechnic Pollution (mandatory in such cases) confirmed that the risk of setting off an explosive device during operations had to be taken very seriously.

A risk identified but not localized

The figures speak for themselves: on aerial views of the site taken after the bombing, no fewer than 58 craters are counted, and it is commonly accepted that at the time, around 10% of aerial bombs failed to explode on impact… Moreover, exploration of the available archives has failed to turn up any trace of a clearance campaign in due form after the war.

To precisely locate possible shells, bombs, rockets or grenades, a pyrotechnic diagnosis is usually recommended. But this operation, which involves detecting the metals present in the soil using various probes (by magnetometry, electromagnetism or even georadar) is impossible here: on this industrial site where a refinery operated for many years and was then destroyed, the soil contains countless metal objects as well as ferrous concrete slabs.

Constraining precautions…

The challenge then is to prevent any situation that could lead to an explosion due to impact or under the effect of vibrations. To ensure that the worksite runs smoothly, the specialists on the Séché Éco Services pyrotechnic clean-up team are then responsible for implementing a series of procedures and working methods:

• Permanent assistance with earthworks: a pyrotechnic remediation operator ensures direct and constant visual control of hydraulic shovel operations.
• Fine-layer earthworks, with gentle, gradual emptying of each bucket to check its contents.
• No hydraulic breaker (BRH) may be used to break up concrete slabs to avoid the propagation of significant vibrations in the ground. Each slab must be routed, and the largest must be pre-sawn and then broken with a bucket.
• Optimizing compaction to ensure soil bearing capacity while limiting vibrations during operations.
• Awareness campaign targeting all those involved on the site to ensure that everyone applies all safety procedures and knows how to react to any eventuality.

You have to imagine what such measures mean on a huge 11-hectare worksite, involving the excavation of over 165,00 m3 of hydrocarbon-polluted soil. A site where operators are equipped with Tyvek suits, resistant to hazardous products and Insulated Breathing Apparatus (IBA), and where work is carried out under a huge containment tent designed to reduce olfactory nuisance for nearby residents.

… And lives saved

But all these efforts will not have been in vain. When a metal object is discovered during excavation operations, everything goes exactly as planned in the procedures. The pyrotechnic clean-up operator immediately interrupts the work and quickly confirms the discovery: it is a 250kg American aviation bomb with two „fuzes“ (or detonators). Immediately the alarm is sounded, all employees are evacuated and gathered at a safe distance, and the specialized Civil Protection services of Montpellier (Déminage 34) are contacted.

Rapidly arriving on the scene, the deminers take note of the situation and manage to dismantle one of the two fuzes. However, it was impossible to remove the second: the bomb could not be moved, and had to be stored securely. The Séché Éco Services teams then lent their support by creating dormant storage in record time, a pit where the device was stored and covered with sand in big bags.

Smooth disposal

Work can now resume on site while the necessary measures to protect the population are organized by the state services. The demining operation will finally be scheduled for the night of March 22 to 23, 2025. Civil security plans a perimeter of around 200m, which includes part of the city center and must be completely evacuated, as well as a mandatory containment zone of 450m involving between 4,000 and 5,000 inhabitants. The operation itself consists of cutting out (by abrasive water jet cutting) the body of the bomb to extract the second fuse. This, consisting of a small explosive charge, will be destroyed on the spot, while the finally disarmed bomb will be taken to a nearby quarry for destruction.

Hearing the detonations in the distance the members of the pyrotechnic clearance team and all the collaborators on site felt both a certain relief and, above all, great pride. Thanks to their efforts, cool-headedness and professionalism, there were no injuries, the rehabilitation of the site was able to resume and they were able to assist the Civil Security agents in preserving the population.