Infants under six months are the most vulnerable of all. "They don't have the mechanism to preserve body heat," said Mark Joffe, director of emergency medicine at St. Christopher's Hospital for Children.
Joffe warns parents to monitor their children closely.
"Some children playing outside, playing to exhaustion, will exercise bad judgment," Joffe said. A child who comes in cold and numb should be wrapped in blankets and allowed to warm up "passively."
If there is continued muscle rigidity, paleness and lethargy, the child may have suffered more severe hypothermia (lowering of body temperature) and need medical treatment.
Blistering or extreme reddening of an area may mean frostbite, which again calls for medical treatment.
Q: What's the best way to dress for extremely cold temperatures?
A: The key word is layering. "Layers of anything can help keep you warm," said John Boulle, store manager at Eastern Mountain Sports in Ardmore.
A hat of some sort is important, because if the outdoor temperature is 20 degrees, more than 40 percent of your body heat loss will be from your head. At 5 degrees, more than 70 percent of the heat loss will come from your head.
As for those high-tech fibers - with names like Thinsulate, Hollofil, Polarguard - they all work on the same principle as old-fashioned down. "What they basically do, they form pockets" that trap the body's heat, Boulle said.
If you're outside working up a sweat - jogging, chopping wood or ice skating - the one thing you don't want right next to your body is cotton. ''Cotton can take forever to dry and you'll feel much colder when that stays against your skin," Boulle said.
Q: Is it alright all right to walk the dog in weather like this?
A: Yes, but the smaller the pooch and the shorter its fur, the less time it should spend outside. So says Ken Drobatz of the University of Pennsylvania Veterinary Hospital.
A shaggy sheep dog or a hefty Labrador can have a romp as long as it doesn't slip on the ice or get rock salt cuts on its paws.
Cats probably ought to stay indoors.
Q: What about horses? Will they be safe?
A: Horse blankets were probably invented for weather just like this. But as long as the horse is out of the wind and the elements, it will do fine with or without a blanket.
The biggest problem will be making sure there's enough drinking water,
because troughs and pails will freeze.
Q: If the lock on my car door freezes, what should I do?
A: Do not, repeat, not pour hot water on the lock. It may bring temporary relief, but if the water then refreezes you're in worse shape than when you started.
It's better, says Garvin Kissinger of AAA Mid-Atlantic, to warm your car's lock with a hair dryer.
Heating your key with a cigarette lighter will sometimes enable it to penetrate the ice, but watch out for burned fingers. Some chemical lock de- icers are available at stores that carry auto supplies, Garvin said.
Q: Will the gas freeze in my gas tank if it is nearly empty?
A: The good news is, the gas won't freeze. The bad news is, the condensed moisture in the tank will. And when it does, this ice can clog the fuel line, preventing gasoline from reaching the engine.
The easiest way to avoid this is to keep the tank at least half full, according to Louis Carfagno of the service department at Don Rosen Mazda in Bala Cynwyd. Dry gas, a fuel additive available at auto supply stores, also helps reduce the moisture.
Q: What should I carry in my car during extreme cold?
A: Kissinger says every motorist should carry a blanket (to keep warm in case you're stranded), shovel, scraper, jumper cables and some type of sand or
kitty litter for traction if you get stuck in snow.
If you become stranded, make sure that the car's exhaust pipe is clear and that a window is opened a crack so you won't be overcome by carbon monoxide exhaust.
Q: Should I remove a car phone, tapes and other such items from my car and bring them inside?
A: The cold probably won't hurt your car phone. Extreme cold can make tapes brittle, though, so it might be wise to bring them in the house.
Q: Does the cold cause other car problems?
A: Kissinger said AAA has gotten a lot of calls from people who turn on their engines to warm up their cars and then go back into their houses. When they return, they discover they've locked themselves out of their idling cars.
"With power door locks, it's easy to lock yourself out," he said. "It's almost an automatic reflex when you leave your car."
Q: How can I get rid of ice on my walk or driveway?
A: This is a tough one. Rock salt will melt through ice, but you'll still need a shovel and a lot of digging to scrape off the ice.
Q: How does rock salt melt ice, anyway?
A: Salt breaks down the crystalline structure of ice. Also, when salt mixes with water it lowers the freezing point of the water, making it harder for ice to form in the first place, said George Palladino, vice chairman of the chemistry department at the University of Pennsylvania.
Any salt - even the kind in your salt shaker - will work. But using kitchen
salt is a pretty expensive way to clear the walk.
Rock salt is most effective for temperatures between 20 and 32 degrees. It will melt ice at a slower rate even at subzero temperatures.
Q: Will rock salt damage my car?
A: Yes, a buildup of salt on your car can cause metal to rust. When the weather is warmer, make sure you wash away the salt buildup on your car.
Q: Does rock salt harm plants?
A: Yes. It is "very bad for most plants," says Rick Lewandowski, horticulture director at the Morris Arboretum. "Azaleas and most garden shrubs can be damaged by salt. If you must use salt, remove as much of the ice and snow as possible with a shovel and salt sparingly."
Lewandowski said another chemical, calcium chloride, will melt ice without damaging plants as much as rock salt does. He also suggests using sand or cinders to give traction on ice, if you are concerned about harming your plants.
Q: Will the severe cold harm my backyard plants?
A: Some shrubs - such as boxwoods - are very sensitive to the cold. You might want to wrap them in burlap or put mulch around their roots, especially if they were planted or transplanted in the last few months, Lewandowski said. But snow and ice are actually good insulators and help protect plants during the winter, he said.
In extreme cold, broad-leafed evergreen plants, such as rhododendron, lose moisture and can dry out. Lewandowski suggests spraying their leaves occasionally with antitransperants sold in garden supply shops.
Q: Does anybody who's sane look forward to weather like this?
A: There are a few.
At the Morris Arboretum, scientists have been wanting to study the question of whether plants like Southern Magnolias and Japanese Camellia can survive the extreme cold that sometimes afflicts our region.
"I've been looking forward to below-zero temperatures," Lewandowski said.
"It's just what I've been waiting for."