The cause of this disaster is actually still under investigations. There are many possible causes that may produce the explosions. This warehouse stored many toxic chemicals which nobody knows how many type of chemicals inside it but for sure it has a very dangerous chemical that could produce a very big explosion such as ammonium nitrate, potassium nitrate, calcium carbide and many more. The most dangerous chemical is calcium carbide which when it reacts with water it will produce an acetylene where it is a very highly volatile gas. This gas could explode if sprayed by firefighter hoses. This Flammable gas can also ignite 20 Tons of TNT inside the warehouse.
The second possibilities is carelessness of employee in handling a toxic chemicals