I know orcas are smart, but... knowledge of chemistry??
This movie was admittedly far-fetched but enjoyable enough until the explosion scene.
1) How did the orca know what pipes are, much less that they contained petrol?
2) How did it know what petrol is, and that it is combustible?
3) Even if it may have known about fire, how did it know that there was a naked flame inside the house?
... and most of all..
4) How did it know that mixing the fire and the petrol would cause an explosion?!
Even if we play along with the film's exposition about the animals possibly being even more intelligent than people, there is no possible way it could have learned such things, given the limitations posed by its environment.