A release of hydrocarbons and hydrofluoric acid in the refinery's alkylation unit caused a ground-hugging vapor cloud which rapidly ignited, leading to three separate explosions minutes apart from each other.

However, shortly after 4:00 am, a leak of liquefied hydrocarbon gas (mostly propane) containing about 2.5% hydrofluoric acid (HF) developed from a ruptured pipe elbow at the discharge of a pump.

At 4:12 am, the control room operator attempted to activate the water cannons which were designed to reduce airborne HF through vapor suppression, but the system failed to respond.

One field operator attempted to walk to the water pumps to manually activate them but reported they were too hot at the time to approach.

Then, at 4:22 am, a vessel containing flammable hydrocarbons (primarily butylene, isobutane, and n-butane) ruptured and caused the largest blast, a boiling liquid expanding vapor explosion (BLEVE).

[1] The report stated that a corroded elbow pipe, installed in 1973, ruptured and caused the initial leak.