I have no idea if the news of this has made it to the US, but it's a big story in Britain....one of my collegues lives about 35km away and was talking this morning about hearing the blast...
view thread124-142176 where the postulation is that this was a vapour cloud explosion.
The effects at what appear to be some distance from the blast, appear to endorse the views expressed in that thread.
The link you posted shows some impressive views of the site.
The earliest news report I read suggested that the cause might have been due to miantenance work... but this was probably just journalistic licence. The vapour cloud suggested nature of the blast would suggest, as any such event would have to, that there were several contributing factors to set up the conditions and then a trigger event i.e. not one thing that went wrong but many .... (my journalistic licence!).
Be interesting to know just what that combination of events/failures was or could have been.