Want more details? This is from an NTSB statement: At the time of the explosion, three of the Norway's four main propulsion boilers were in normal-in-port operating status supplying steam to electrical generators and auxiliary equipment while the ship was moored to the dock in Miami. Boiler no. 21, located in the forward starboard side of the boiler room, was secured and was not in operation at the time. Boiler no. 23, located aft of boiler no. 21, was the boiler involved in the explosion. No maintenance was being carried out on boiler 23 at the time of the explosion.
NTSB investigators are closely examining boiler no. 23 to determine why it exploded. The investigation has progressed slowly because of the extreme safety and health conditions in the damaged boiler room. Investigators have had to don personal protective equipment, including respirators because of the high level of asbestos. Asbestos was used to insulate the steam piping throughout the boiler room. The area is not well ventilated and is poorly lighted. The force of the explosion has ripped away walkways, making access difficult. Because of the heat, poor ventilation, and the necessity to wear protective equipment, investigators are limited to about one hour in the space at one time, after which they must go through a decontamination process.
Damages to boiler no. 23 were extensive. The outer casing is ruptured allowing the interior of the boiler to be visible on the starboard aft section. The explosion knocked out and opened doors three decks above the boiler. Fuel oil heaters on the starboard side of the boiler were blown partially from their mounting brackets and were found to be hanging loose.
Investigators have examined a water wall header that was found to have significant material failure. The header is one of three separate drums of the boiler that runs the length of the boiler. The header is a component of the system that facilitates in the circulation of the boiler steam-water cycle. The NTSB investigators also report that damage, beyond the boiler room itself, included areas adjacent on decks four and five, particularly bulkheads, doors and frames. Some crew cabins on "Caribbean" deck were severely damaged - cabin doors were actually blown out of their frames.
The investigation continues onsite, at least for the next few days, as the NTSB continues to collect data. A final report is not expected for at least months if not longer.