Apparently the werehouse had 2,700 tons of Amonium Nitrate stored there that had been confiscated several uears earlier from a ship.
This chemical in its own right is not explosive ( It's an oxidising agent ) but if in combination with a flammable source, such as gas or oil, will facilitate an explosion.
From the pictures it looks like a fire was already in progress before the explosion so the flammable agent was there heating up the Nitrate.
See
ANFO
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History is much like an endless waltz: The three beats of war, peace and revolution continue on forever.
However history will change with my coronation - Mariemaia Khushrenada
