(Al Jazeera) Iran’s President Pezeshkian visits injured, site of deadly port explosion.

The cellphone video shows an initial deflagration (fire or low-order explosion) followed by a detonation (blast)  estimated in the range of 100 tons to multiple thereof. The size of the blast cannot be attributed to an air-dropped weapon in daylight. Denials by Iran that military explosives, or rocket fuel, were present are not credible; a detonation of that size requires large quantities of those substances, or a fuel-air munition for which there is no evidence.

The initial deflagration may have concealed the preceding detonation of a small explosive device. Quoting AP,

Private security firm Ambrey says the port received missile fuel chemical in March. It is part of a shipment of ammonium perchlorate from China by two vessels to Iran, first reported in January by the Financial Times.

Several media have misidentified the chemical as sodium perchlorate, a common industrial chemical that can oxidize combustible substances, but has no explosive properties in isolation. Ammonium perchlorate contains both oxidizer and fuel, supporting both deflagration and detonation. It requires only additives for a practical rocket fuel. Yet  the NY Times references sodium perchlorate:

The security firm Ambrey told The Associated Press that there were indications that the blast resulted from improper storage of sodium perchlorate at the port…

as does CNN:

The New York Times reported Sunday that a person “with ties to Iran’s Islamic Revolutionary Guard Corps said that what exploded was sodium perchlorate, a major ingredient in solid fuel for missiles. The person spoke on condition of anonymity to discuss security matters.”

Storage of ammonium perchlorate at the  port implies Houthi recipients.

There is no evidence of an air-dropped weapon, which lacks guaranteed deniability.

There is no evidence of cooking-off, when finished munitions are lofted by thermally induced explosion.

Explosion of ammonium perchlorate can be easily induced by a small pyrotechnic device.

There is bias here towards sabotage versus accidental ignition.

If a source did, in fact, identify the chemical as sodium perchlorate, distraction would be the motive.

There is nothing to suggest an industrial accident, which would require the substitution, in name only, of sodium perchlorate, intimately mixed with an unspecified combustible substance. Nevertheless, this will likely be Iran’s choice of explanation, avoiding disclosure of supplies destined for the Houthis.