Two young men were rescued by first responders after falling through the ice on a pond in New York's Central Park on Tuesday afternoon. The pair survived, but their ordeal illustrates the dangers that lie beneath even a solid-looking ice-covered lake.

“The three types of people most likely to find themselves stranded on thin ice, or freezing beneath it, are teenagers, dog owners, and Good Samaritans attempting to rescue teenagers and dog owners,” New Yorker scribe Ben McGrath wrote in March 2011.

The maxim seems to hold true in Central Park. In 1991, a 42-year-old man named Robert Padden died after he ran out onto a Central Park lake to try to save a drowning wire-haired terrier. About 20 joggers and pedestrians tried to form a chain to reach Padden and the dog, but couldn’t break through a 20-foot wide ring of ice surrounding them.

Police officers managed to pull Padden out, but he suffered a heart attack while trying to stay afloat in the frigid water and died that night. The dog also perished.

The best way to avoid a nasty shock is preparation. In city parks, that means sticking to the trail and not venturing out on pond surfaces.

But sometimes, for work or play, going out on the ice is a reality -- one that can have dangerous consequences. So if you must venture out there, be prepared.

The Cold Regions Research division of the U.S. Army Corps of Engineers offers practical tips for going out on uncertain ice. Don’t go alone. Rescue equipment is also strongly advised, like ropes or personal flotation devices. There are also special ice rescue picks worn by ice fishermen that hang on a string threaded through the sleeves of your jacket – think a child’s mittens – and can help you claw your way back onto more solid ground. At a minimum, carry a stick and rope.

Another basic requirement for venturing out onto an icy lake is equipment to test and measure the thickness of the ice: an ice chisel, a drill or auger, and a measuring tape or stick.

According to the Colorado Parks & Wildlife office, if the ice is two inches thick or less, stay off. Four inches is good for a person to walk on; six will hold a snowmobile or an ATV; eight to 12 inches is safe to drive a car or small pickup truck across, while 12 to 15 inches is required for a medium pickup truck.

However, not all ice is alike. Clear ice is stronger than white ice, which is filled with bubbles. While four inches spread over a square 30 feet by 30 feet of clear ice can support a ton, it takes eight inches of white ice to hold up that same weight. You should avoid ice that isn’t flat, or ice that’s wet. Areas where water might still be moving, like the outlets and inlets of ponds, are more likely to have thin ice.

New ice is generally stronger than old ice, thanks to the chemical nature of the bond between water crystals.

“As ice ages, the bond between the crystals decays, making it more dangerous and weaker even if melting has not occurred,” Ohio State university experts Gary Graham and Thomas Bean wrote in a factsheet.

If you do fall into the ice, Wired’s How-To Wiki has several important tips for getting out quickly, before you risk losing parts of your body to frostbite. One of the first things that’s important to remember is not to panic. The shock of the cold water will probably cause you to gasp for air, but it’s important to try and take slow, deep breaths. The ice from where you fell is probably strong enough to support you, so it’s best to turn around and try and exit the water from where you fell in.

With your arms out over the ice, shimmy up so your torso rests on the more solid ground. Then, use a dolphin-type kick to lever yourself out, and roll – don’t walk – along to shore.

“Resist the urge to rub your arms and legs (which would send the cool blood from your extremities straight to your core) or gulp hot liquids (which would trigger a rush of blood to your skin),” Wired writes. “Strip, wrap your torso in blankets, and sip a tepid decaf beverage.”