A discarded cigarette butt was the likely cause of the nighttime fire that broke out in March while the cruise ship Star Princess was sailing in the Caribbean, British accident investigators reported Oct. 23.

Britain's Marine Accident Investigation Branch made official what had long been speculated: that the March 23 fire aboard the Star Princess was probably sparked by a cigarette tossed overboard that ignited combustible materials on a protruding cabin balcony.

The blaze swept upward, spreading from balcony to balcony, damaging some 300 cabins on the ship before it was brought under full control. One passenger died (not directly from the fire) and 13 others were hospitalized for smoke inhalation.

The investigators found that the polycarbonate partitions, polyurethane deck tiles and plastic furniture on the balconies were highly combustible and produced thick black smoke when burned.

The investigators also praised Carnival PLC, owner of Princess Cruise Lines, for its speedy response to the fire.

Stephen Meyer, the chief inspector of marine accidents, said Carnival expected to replace all combustible dividers on its 81 vessels with non-combustible ones by the end of 2006.

The investigators said their inquiry had already had a "significant impact" on both the cruise industry and regulations relating to cruise ship balconies.