Are polar cruises safe? Not all ships are equal.

The sinking of the MS Explorer near Antarctica's King George Island Friday has renewed attention to the potential dangers of operating passenger vessels in remote polar areas.

The ice-reinforced Explorer was a veteran of the polar cruise-ship trade. It had made dozens of voyages to the Arctic and Antarctic since 1969, safely transporting thousands of tourists to see penguins and polar bears, glaciers and icebergs, though the ship was evacuated at least twice after Antarctic groundings.

But experts note that the crews of such ships must deal with floating ice, unpredictable weather, and substandard nautical charts – all of which can create life-threatening situations.

"These are warning signals," says Jim Barnes, executive director of Washington-based Antarctic and Southern Ocean Coalition. "You add up the incidents and I think it's clear that standards need to be strengthened to reduce risks to human safety and the environment."

Cruise-ship tourism has boomed in both polar regions. The number of cruise-ship passengers in Greenland has more than doubled since 2003, while Svalbard, in the Norwegian Arctic has seen steady growth. In the 1980s, Antarctica often saw fewer than 1,000 tourists per year; this past season, cruise ships brought 37,552.

This year saw several serious incidents. In January, 294 passengers on the Nordkapp had to be evacuated after the 11,000-ton ship struck a rock at Deception Island, Antarctica. In August, 23 tourists were injured – two seriously – when a piece of glacier fell into the sea, throwing a wave of ice and water onto the deck of the Alexey Maryshev in a Svalbard fjord.

"These regions have harsh conditions, and if you make one small mistake it can have very serious consequences," says Miriam Geitz of WWF-International's Oslo-based Arctic program. "Now we see a lot of large cruise ships coming in the summer that are not made for these areas. You don't want to imagine what would have happened if the Explorer had been carrying one or two thousand people."

Last year, Princess Cruise Lines caused a stir when it sent the Golden Princess, a 109,000-ton megaship with five pools and 16 decks, to Antarctica with more than 3,500 passengers and crew. Its sister ship, Star Princess, will return in January. Neither ship is ice-reinforced.

"It's insane to be taking ships down to Antarctica that are not ice-strengthened and lack double hulls," he says, adding that large ships carry not diesel but heavy fuel oil, which causes far more damage if it spills. He supports recent efforts by the Antarctic Treaty Organization – whose 46 member states provide what little government the southern continent has – to require reinforced hulls in the region.

But those are no guarantee. "Any ship in polar regions can get itself in trouble if it operates beyond its structural strength," says Claude Daley, a professor of naval engineering at Memorial University in St. John's, Newfoundland. "It's something like driving off-road – there is always a bigger rock out there than the one you can safely drive over."

Mr. Daley says compartmentalization of the hull – not its thickness – is the real line of defense against sinking. "There's always something that can come along and bang a little hole in you," he notes, which is why international regulations require ships to be divided into watertight chambers. It also raises questions as to how Explorer could have sunk from a single fist-sized hole, as initially reported.

The industry has made efforts to regulate itself. Members of the International Association of Antarctica Tourism Operators (IAATO) and the Association of Arctic Expedition Cruise Operators (AECO) follow guidelines such as limiting the number of tourists landed in sensitive areas, and restricting proximity to wildlife and icebergs.

"The industry has taken responsibility ... and imposed regulations that go far beyond the laws of the nations we operate in," says Frigg Jorgensen, general secretary of Svalbard-based AECO. "When people experience these great wilderness areas, they understand the necessity of taking care of them."

But some companies have declined to join. In Antarctica, Norwegian Cruise Lines and Discovery Cruises flout IAATO rules prohibiting ships with more than 500 passengers from conducting Antarctic shore landings. "We're very disappointed that they've chosen not to cooperate," says IAATO's executive director, Denise Landau. "As soon as Explorer put out a distress call, we had three ships diverted there within a few hours, and that's due to the close working relationship our ships have with one another."

Aqqaluk Lynge, a leading political figure in Greenland, warned of the dangers of cruising near icebergs at a conference in September. "These icebergs are dangerous and these ships shouldn't be here," Mr. Lynge told the Monitor while aboard the ice-reinforced MS Fram near Ilulissat, Greenland. As he spoke, the Explorer was anchored a stone's throw away, a large chunk of floating ice snuggling up against her bright red hull.