Washington ( CNN ) -- The fire that crippled the Carnival cruise ship Triumph started with a leak in a fuel-oil return line running from one of the ship 's engines , the U.S. Coast Guard said Monday . Leaking oil hit a hot surface , starting the fire , said Teresa Hatfield , the lead investigator for the Coast Guard . Hatfield said there was no indication the leak in a flexible hose section was intentional . `` Fire suppression was immediately activated by the crew , first by waterfog and then by ( carbon dioxide ) . They did a very good job , '' Hatfield said . `` We are looking at the cause of the fire and why the ship was disabled for so long , and we are also looking at the crew response to the fire as well . '' Hatfield said the investigation will last for several months . The Coast Guard said it has conducted 21 interviews with passengers and crew members since Thursday , when investigators boarded the ship while it was still at sea . Hatfield said the oil return line is one of the items that is routinely inspected , but she did not say when it was last inspected or describe its condition at that time . Vance Gulliksen , a spokesman with Carnival Cruise Lines , told CNN Monday that the ship 's last scheduled Coast Guard inspection was on November 15 . Gulliksen also said the cruise line agreed with the Coast Guard 's determination of the origin of the fire . Coast Guard spokesman Carlos Diaz said the line ran from the ship 's `` number-6 engine '' to a fuel tank . The Triumph was on the third day of a planned four-day cruise from Galveston , Texas , to Mexico when the fire broke out and brought the trip to a halt . It was carrying more than 4,200 people , including 3,100 passengers . The Triumph was eventually towed into port in Mobile , Alabama , Thursday night , and the last passengers disembarked Friday . Stranded on the crippled ship , passengers and crew lived with worsening conditions , as toilets stopped working , and waste spilled onto floors and into hallways . Passengers had to use plastic bags to collect their waste . Passenger Cassie Terry described the ship as `` a floating toilet , a floating Petri dish , a floating hell '' in a lawsuit filed Friday against Carnival for unspecified damages related to the cruise . Passengers reported long lines for food , shortages of fresh water and widespread boredom . Many passengers slept in hallways or outside to escape the odors and heat below decks . Patrick Cuty , a senior marine investigator for the Coast Guard , told CNN Sunday that investigators had located the area where flames erupted in the engine room . `` We know that the fire originated in front of a generator , '' Cuty said . `` You can see the ignition marks on the wall . '' There are three generators in the engine room where the fire broke out . Three other generators are in a second engine room that was n't involved in the fire , Cuty said . The same ship encountered a problem in January with its propulsion system , according to a notice posted on the website of Carnival senior cruise director John Heald . On Saturday , Carnival crew members were bused to and from the ship to help with the clean-up . One housekeeper told CNN it was n't pleasant work but said it had to be done , and the crew was willing to do it . Passengers have praised the crew for its response during the ordeal . Because the Carnival Triumph is a Bahamian-flagged vessel , the Bahamas Maritime Authority is the primary investigative agency and will work with the Coast Guard and the National Transportation Safety Board . Investigators pulled the voyage data recorder , a device that records alarms , voice communications on the bridge , engine speed , navigation information and rudder angle , Cuty said . It appears that the fire suppression worked as designed , Cuty said Friday . The engineer who was on watch around dawn February 10 saw the fire ignite over a video feed and immediately notified the bridge , Cuty said . On crippled cruise ship , icky jobs fell to 'amazing ' crew . Lawsuit filed over 'floating hell ' cruise . CNN 's Jim Barnett contributed to this report .
NEW : This means the product will ship as received by the manufacturer, sealed, with all advertised components, and with the manufacturer warranty. The fuel line ran from an engine to a fuel tank . There is no indication the leak was intentional , a Coast Guard official says . The crew is praised for doing a `` very good job '' containing the fire .