sentences:  A fraction of the radioactivity was expelled with the gas, lava, and slag.The lava solidified on the floor of the gallery, but the particulates and the gaseous products formed a cloud which culminated at about 2,600 m of altitude, leading to radioactive fallout detectable for a few hundred kilometers downwind from the site.According to the witness Pierre Messmer, some seconds after the ground trembling caused by the explosion, the spectators saw “a kind of gigantic blowtorch flame that started exactly horizontal in our direction… This gigantic flame was extinguished rather quickly and was followed by the release of a cloud which was ochre-coloured at first, but then quickly turned black.”
  
  Recordings from devices measuring radioactivity were immediately put under military secrecy.