That is what I have been puzzling over since yesterday...flaring of butane is the only possibly explanation as from what i have read previously that is what crosstex had stored in the cavern...the only reason for flaring off he butane would be as posted above that there has been an increase in pressure...the only way that pressure would be increasing in the cavern is a breach allowing infiltration in to the cavern of something else causing the gas to be forced upwards...

they did state that the only way the gas would become a hazard is if water or similar was pumped in to the cavern because the butane is heavier than air therefore will not exit the cavern unless under pressure.....

Yep was definitely Butane according to this article..

[link to theadvocate.com]

so something is putting the butane under pressure to get it to rise in the cavern...sound like this cavern is breached!