[TomGuy]

freighter that was carrying a chemical commonly used in fertilizer

Fertilizer is known to be explosive when mixed with certain other chemicals and petroleum products (diesel fuel).

Wonder what the "chemical" being transported is...and how volatile?

[Constitution Day]

FNC Article:
Sunday afternoon, the captain reported to the INS inspector that the four Pakistanis had not returned to the ship.
The Progresso then departed for Savannah, Ga.

You said:
Fertilizer is known to be explosive when mixed with certain other chemicals and petroleum products (diesel fuel).
Wonder what the "chemical" being transported is...and how volatile?

I wonder too.
Makes me think about nuclear facilities along the coast... such as the DOE's Savannah River Site, near Aiken, South Carolina.

I don't know how close that is to the ocean.