The ‘explosion’ heard across Normandy was in fact caused by a sonic boom from a French army fighter jet Pic: VanderWolf Images / Shutterstock

A loud ‘boom’ heard across Normandy on August 4, which provoked fears of an explosion in the area, has been revealed to be a fighter jet passing the sound barrier.

Residents from Rouen (Seine-Maritime) to Bayeux (Calvados) heard the noise just after 16:30, and many took to the internet to express astonishment and fear at what the sound could mean.

This was especially true in Rouen, where memories of the disastrous Lubrizol Seveso factory explosion of 2019 are still close to the surface. 

Read more: French city on alert after chemical plant blast 

Read more: Explainer: What are Seveso risk sites and where are they in France? 

One Twitter user simply asked: “Did you also hear the explosion in Normandy?”, while another, Romain Mollet, said: “It's not that we're unused to mysterious explosions in Haute-Normandie, but it would be nice to have some explanations quickly.”

Luckily for residents, it did not take long for the local prefect to confirm that the source of the noise was nothing to worry about, and was just an army fighter jet passing the sound barrier.

This causes what is known as a ‘sonic boom’, which can sound like a loud explosion or bang. The noise can be heard hundreds of kilometres away.

Vous habitez en Seine-Maritime et vous avez entendu un bruit sourd il y a quelques instants? Il s'agit d'un passage du mur du son par un avion militaire @Armee_de_lair pic.twitter.com/r6C8AmQB9G

This kind of military exercise, in which fighter jets go at this high speed, is relatively common in the area. The most recent one before this took place on March 10 (2022).

After the reason for the boom was revealed, some users joked about the pilot’s reasons for flying so fast. 

One user said: “He forgot he had to pick up a drive-through food order at Leclerc.”

The boom came just one day after an explosion and fire at another Seveso factory site in Bergerac injured eight people, one seriously. 

Read more: Explosion at Dordogne chemical factory: low pollution risk for locals

Terrorism alert triggered over France after pilot falls asleep 

Shoeless pilot in stolen plane intercepted by French army jet