In seriousness, we are not being told everything. I have a family member who is a sargeant in the bomb squad at the metropolitan police. That oil refinery was listead as a priority one target as it was simple to disrupt, with maximum damage and effect. Think about it, all someone would have to do is throw a match into one of the tanks, the rest would simply follow.

Also, the disruption is yet to be felt, especially by heathrow and gatwick as they have dedicated pipelines from that refinery for their aviation fuel