Exploding boules balls

A local festival, a pleasant summer’s evening, a friendly game of boules - and suddenly a deafening bang. Not from a firework or a cracker, but from an exploding boules ball.

The incredible explosion, which occurred in Nettetal, Germany, on the Dutch border, left a hole in the tent and a crater in the ground. Fortunately, nobody was hurt in the incident; the revelers merely got the shock of their lives. But how can boules balls just blow up like that?

Following similar cases in Switzerland in 2009, a team of Empa experts carried out an in-depth investigation ( Video in German). Their conclusion: the cheaply produced, thin-walled balls were filled with mortar to make them heavier. Unfortunately, the mortar was damp and contained iron filings, which corroded. This produced hydrogen, which created high pressure inside the boules balls. Eventually, a shoddy weld seam on the cheap ball burst and caused the blast.

More accurate tests are required to ascertain whether or not the same causes led to the explosion in Nettetal as in Switzerland. At any rate, the press reports that the balls in the boules set, which didn’t blow sky high, have since been secured by explosives experts.