Twenty people were hospitalized after fire broke out aboard the Carnival cruise ship Ecstasy on Monday

(CNN) -- About five million people are expected to take a cruise this year, and travel experts say it's one of the safest ways to spend a vacation.

But the frightening images of a fire on board the Carnival ship Ecstasy this week could change a few travelers' minds.

"Of course a fire on any ship and especially a cruise ship is a very scary proposition," said Howard Moses, president of the cruise-only travel agency, The Cruise Authority. "The cruise lines go to incredible lengths to prevent this from happening. This is a very unfortunate and very isolated incident."

Indeed, nothing of the magnitude of the Ecstasy fire has happened on a major cruise line in over a decade. Modern ships are considered very safe.

But some ships are sailing without such modern conveniences as automatic sprinklers because of exceptions made under international law allowing some older vessels to delay phasing them in until the next year or two.

Older ships tend to be a greater fire hazard. All eight deaths from cruise ship fires in U.S. waters over the past two decades were on older ships.

Newer ships like the Ecstasy are not immune -- and the Ecstasy did have automatic sprinklers.

"I think it really indicates how important it is that people pay attention to the lifeboat drill," Moses said. "This would indicate that if nothing else you should pay a little attention to what's going on so that if a situation did occur that you would have some idea of what to do."

Safety officers go through extensive training, and cruise regulations have been strengthened, including requirements for smoke detectors and lights along the floor to direct passengers to exits.

Following an investigation into a 1996 fire in the main laundry aboard the Universe Explorer off the Alaska coast, the National Transportation Safety Board issued a list of safety recommendations in April, including a request for the U.S. Coast Guard and International Maritime Organization to research "the adequacy of heat and smoke detectors for use in high-risk fire areas, including laundry spaces."

But fire isn't the only problem: dozens of people became ill on one cruise ship a few years back, and a similar incident occurred on another ship off Alaska just this month. Veteran travel agent Helene Dolan gives her clients all the facts about a ship, and her own opinion of a vessel's fitness.

"I will say, 'This particular cruise line or this ship on this particular cruise line is not what you're looking for, absolutely,'" she said.

But she added that she believes, overall, vacations by cruise ship are nothing to worry about.

Many people agree. Sally Kendall's son and his new wife are honeymooning aboard the Holiday, but she's not worried.

"I still feel confident that it's safe," Kendall said.

Kendall isn't the only one -- there are, after all, still millions of passengers cruising yearly.

CNN Correspondents Anne McDermott and Stephanie Oswald contributed to this story.