The last few years have seen a rash of engine fires aboard cruise ships -- many of which have led to an almost total loss of electrical power. Passengers on board the Carnival Triumph are but the latest to endure the consequences: a lack of hot food and water, a loss of air conditioning and refrigeration, sanitation systems on the verge of collapse.

Beyond these inconveniences are more serious issues: a loss of engine-power to the vessel and the lack of stabilization. If a ship is on the high seas in rough weather there is a greater risk of injury as the vessel pitches and rolls. The situation is further aggravated if tugs are days -- not hours -- away.

The U.S. National Transportation Safety Board warned after one such fire that "Hazardous situations that may result from a ship losing propulsive power include vessel grounding, inability to avoid severe weather conditions, and passenger evacuation at sea."

No backup power

Many wonder why such huge ships have inadequate backup power in the event of an electrical failure.

Modern cruise liners are like floating towns, 10 or 15 floors high. They carry 3,000 to 4,000 passengers and draw an immense amount of electrical power. If the main power supply fails, auxiliary systems can supply only a fraction of what's needed.

Jay Herring, a former senior officer with Carnival Cruise Lines who served on the Triumph, said: "The Triumph is normally powered by six diesel-electric generators. Each one is the size of a bus, and 80% of the electricity used on board goes towards propulsion."

"So if you take those away even if you have a backup generator, you're only going to be able to provide lighting in limited areas and you're certainly not going to be providing ventilation for a vessel that is the size of three football fields."

The 1,000 toilets on board, for example, require a massive amount of electricity to work the suction system.

As for the generator airlifted to the Triumph on Tuesday by the U.S. Coast Guard, Herring said: "It would only be like a Band-Aid on a gashing wound. It might provide a little bit of relief but there's no way that we're going to be able to drop a backup generator for propulsion."

Catalog of engine fires

There has been a spate of engine fires aboard passenger ships around the world in recent years.

2011: In the Indian Ocean, the Costa Allegra suffered an engine fire that left it without power for three days in tropical heat of nearly 100 degrees Fahrenheit. The fire broke out in the electrical generator room. There were no casualties but tugs were needed to tow the ship to Mahe in the Seychelles. As with the Triumph, backed-up toilets and a lack of water were among the problems. Passengers said after disembarking they were fearful of pirates or rough weather in the stranded ship.

2011: The Azamara Quest -- in the midst of a Southeast Asian cruise -- was disabled by an engine fire and drifted in southern Philippine waters. Propulsion was restored the next day and the vessel limped into Sandakan in Malaysia.

2011: The Ocean Star Pacific, a Mexican liner with 522 passengers and 226 crew, was stranded by a generator fire a few miles off the Pacific coast of Mexico. The passengers were evacuated.

2011: On September 15 a fire in the engine room of the MS Nordlys killed two of the crew. All 207 passengers were taken off the ship, which was off the coast of Norway.

2010: During the early hours of November 8 an engine room fire on the Carnival Splendor 200 miles off the coast of Mexico disabled the ship. The fire broke out in the aft engine room and took several hours to extinguish. No one was hurt but the cruise director, John Heald, said later that "the smoke was so intense and so thick that, even with breathing apparatus on, the teams could not get close to the source" of the fire.

Carnival CEO Gerry Cahill said later there had been a "catastrophic failure of diesel generator No. 5." But at the time he said he doubted any of the other ships in the company's fleet were at risk.

2009: A fire started in the engine room of The Royal Princess while on a cruise in the Mediterranean, with 1,126 people on board. The fire broke out soon after the ship left Port Said. Partial engine power was restored the next morning.

These incidents were caused by different problems. In the case of the Splendor, the heat generated by the fire damaged two engine control switchboards directly above and melted electrical cabling, causing a total loss of electrical power on board and the failure of the forward engine room.