It was only a short day hike on a beautiful autumn morning on a park trail loop a couple of hours from home. But on the decline back to the trailhead you twisted an ankle -- feels like it might be broken.

Sitting on the ground where you fell, your situation slowly comes into focus: You can't get a cell phone signal, no one knows where you are or when you're expected home and you didn't bring water, rain gear or a lighter. The sun is setting and dark rain clouds are blowing in fast.

In two hours you're sitting alone in the dark, in the mud, soaking wet and shivering. Your throat's dry, ankle's throbbing, there's something moving in the bushes and it's 10 hours to daybreak.

Gulp!

This may be the wrong time to remind you of the old Boy Scout motto. But the folks at Venture Outdoors had "Be Prepared" in mind when they scheduled a Wilderness Awareness and Survival Class recently at the Harrison Hills Park Environmental Learning Center, in Natrona Heights. Instructor Amy Trulik, an outdoors enthusiast and veteran of the Tom Brown Jr. Tracker School, gave about 30 participants a primer on wilderness survival.

Outdoors preparedness doesn't necessarily mean surviving for weeks far from civilization in the world's harshest conditions. In temperate, heavily populated Pennsylvania, an unplanned spill into water, prolonged exposure to rain and wind, or unexpected overnight stay in the woods without the right equipment can result in extreme discomfort -- even death.

Trulik's class covered emergency shelter building, fire starting, finding water, signaling and self-awareness of one's place in nature. Mostly, she said, it was about not getting into a position where you need any of the above.

"If you're out in the woods with absolutely nothing," she said, "how would you survive, and the philosophy that everything you need to survive is there."

After oxygen, the first thing the human body needs to survive is protection from the elements.

"Extreme cold is not required for hypothermia to develop," said Keith A. Snyder of the Pennsylvania Game Commission in an educational press release. "Hypothermia occurs when exposure to the wind, cold and wetness drain heat from the body faster than it can be produced. ... Most cases occur when the air temperature is between 30 and 50 degrees."

Preparedness is essential if you need to build a fire fast using the waterproof lighter or matches, fire starters and dry tinder that you carried with you on a day hike or hunting or fishing trip. If you didn't bring a survival kit or can't get a fire going, at least get out of the elements.

"You don't necessarily have to build a fire if you build a good debris hut," said Trulik. "It's improvising, using found objects to insulate yourself against the cold. Use a log or fallen tree to make a skeletal frame, and layer in branches, leaves and plastic if you can find some."

Survivalists advise to remove wet clothing, wring it dry and put it back on, padding it with found insulating materials.

Long before your body will require food, you'll need drinking water. Don't trust Pennsylvania streams, rivers or lakes to be free of biological or industrial pollution.

"If you get diarrhea in a situation like that, it's about the worst thing that could happen to you," said Trulik. Carry water, even on a short bike ride or day hike. If you need to make potable water, filter it though natural grasses or collect dew in pieces plastic or other found trash.

If you've let people know where you're going and when to expect you back, someone will probably start looking for you within 48 hours. Help them to find you by staying put. Smoke is the best locator -- prepare a pile of green leaves or moss, which produces more smoke, to throw on the fire the instant you hear people, a plane or helicopter. Spell "S-O-S" with rocks or sticks that can be seen from the air.

Accidental overnight stays are often the result of injuries. Twisted ankles and hunters falling from tree stands are common emergencies in Pennsylvania's wild places.

"In my experience over the last 30 years, it's ankles -- either sprained or fractured -- and problems related with not being in shape that cause most outdoors emergencies," said George E, Dvorchk Jr., a doctor from Irwin who stopped practicing medicine and took up outdoors writing. In 2007, Stoeger Books published his "Pocket First-Aid Field Guide."

"First, don't panic," he said. "If something bad happens, sit down and think it through. Even if you didn't prepare well, you can probably find what you need to treat wounds if you look around: branches to support broken bones, a shirt or handkerchief to stop hemorrhages."

Most outdoors emergencies can be fixed long before they happen with just a little foresight. Carry a little knapsack containing waterproof matches or lighter and tinder, water, a space blanket, Ace bandage, string, knife and plastic trash bag, which can be adapted for many uses.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.