This is an excellent video that takes us through the progression of an ammonia (CAT 2 Flammable Gas) explosion.
A contractor working in the engine room reported the smell of ammonia @ 6:04 a.m.
A maintenance worker entered the engine room at 6:24 a.m. and did not smell/see/notice anything unusual!!! I am guessing they did not have a zero leak policy at this facility?!?!
At 6:48 a.m. we can see the contractor re-enter the engine room but the smell was overwhelming and he again exited the room. It is also at this very moment the leak from the vertical insulated vessel becomes apparent. The contractor can be seen exiting quickly, not far from the leak point.
At 6:50 a.m. the conditions inside the engine room change QUICKLY and the camera becomes obscured.
At 7:00 a.m. we have ignition of the vapor and can see the lamented flame travel over equipment/machinery in the room; but still NO EXPLOSION until 37 seconds later.
I have still not received my FOIA documents as this incident must still be under some type of legal review, so I am not yet sure what caused the LOPC that led to this explosion.