An overflow such as this results in the rapid formation of a rich fuel and air vapour. CCTV footage showed such a vapour flowing out the bund wall from around 05:38. By 05:50 the vapour started flowing off the site, near the junction of Cherry Tree and Buncefield Lane. Around 05:50 the rate at which fuel was being pumped into the tank increased dramatically. Initially the fuel was pumped in at per hour, but it increased to about per hour. By 06:01, when the first explosion occurred, the cloud which was initially about deep, thickened to and had spread beyond the boundaries of the site.