In the aftermath of a natural disaster, such as a tornado or hurricane, survival — medical care, food, water, shelter, heat — is your first instinct. Sadly, some of the measures people take to stay warm put them in grave danger from another deadly threat: carbon monoxide poisoning.

Two weeks after Hurricane Sandy’s devastating blow to New York City, which knocked out power to countless homes, emergency rooms saw nearly four times as many people poisoned by carbon monoxide (CO) as during the same two-week periods between 2008 and 2012 combined, according to a study published in Clinical Toxicology.

The cause? During prolonged power outages, many people turned to risky practices — such as running generators and grilling indoors — to cook, warm themselves and light their houses. In Connecticut, most of the CO injuries occurred from people cooking indoors on charcoal grills, running portable generators indoors and using a propane lantern or heater inside, according to another study.

New Jersey, two 19-year-old cousins and best friends described as “joined at the hip” died after fumes from a portable generator just outside the house were sucked through the window of the room where they were sleeping.

"Adequate ventilation is a key component of carbon monoxide poisoning prevention," lead investigator Kelly Johnson-Arbor, MD, of Hartford Hospital's department of emergency medicine, said in a journal news release.

Related: Carbon Monoxide Poisonings: Is Your Family Protected?

A perhaps more surprising source of CO poisonings after Superstorm Sandy were auto exhaust pipes blocked by snow. Lethal concentrations of carbon monoxide can build up in the passenger compartment when the car’s tailpipes are filled with snow, even when the vehicle's windows are opened 6 inches, study co-author Dadong Li, MD, told reporters.

People should examine their vehicles after snowstorms prior to starting the engine “to ensure that the exhaust area is cleared of snow," Li said.

"In addition, people should be advised to avoid sitting in running automobiles during and after snowstorms, unless the exhaust area has been completely cleared of snow, regardless of whether the windows are opened,” he added.

Carbon monoxide poisoning can also occur if snow is blocking home heating vents, researchers found.

Heat isn’t the only reason that families power up generators after a disaster. In another study, researchers studying the aftermath of Hurricane Ike in Texas found that 50 of the people receiving emergency treatment for CO poisoning in one hospital in Houston were under 18. In 75 percent of the pediatric poisonings, the main reason for powering the generators was wanting to watch video games or television.

Confined spaces: How to avoid CO poisoning during a disaster

CO poisoning is the number one cause of accidental death in the United States. The real tragedy, health and safety officials say, is most of these deaths and injuries can be prevented.

Poisonous, odorless and invisible, carbon monoxide gas is given off whenever fuel is burned. If equipment is faulty or if it’s giving off fumes in a confined space without enough ventilation, everything from ovens, water heaters and car engines to generators and charcoal grills can turn a home into a carbon monoxide trap.

Related: Are You Using Your Generator Safely?

The Centers for Disease Control and Prevention offers the following guidelines for preventing carbon monoxide poisoning during and after a disaster:

  • Never use a gas range or oven to heat your home.
  • Never leave the motor running in a vehicle parked in an enclosed or partially enclosed space, such as a garage. “We’ve heard [horror stories] about people heating up their cars in a closed garage during the winter,” says Brian Langkan with Safety Sensor, a company that manufactures carbon monoxide detectors. "The carbon monoxide can seep from the garage into the house fairly quickly.”
  • Never run a generator outside an open window, door or vent where exhaust can vent into an enclosed area; they should be at least 25 feet away from the building. The same warning applies to autos, pressure washers, or any other gasoline-powered engine.
  • Never run a generator inside a basement, garage, or other enclosed structure, even if the doors or windows are open, unless the equipment is professionally installed and vented.
  • Don’t run a pressure washer or any gasoline-powered engine inside the house or basement unless it has been professionally installed. Since a windstorm can blow debris into the vent or flue and block the ventilation, be sure to clean it before using it.
  • Make sure your home has at least one working carbon monoxide detector. Check the batteries once a month or at least twice annually, at the same time smoke detector batteries are checked, and replace them every six to 10 years.
  • If conditions are too hot or too cold, seek shelter with friends or at a community shelter.

Symptoms of CO poisoning include sudden flu-like symptoms, nausea, dizziness, fatigue, headache and irregular breathing; sometimes people get red splotches on their cheeks. If you suspect you have CO poisoning, leave the house immediately and get to fresh air, then call your local Poison Control Center at 1-800-222-1222 or get emergency medical help. CO poisoning can be deadly so immediate medical attention is essential.

“You need to get out of the area, get fresh air and seek medical advice right away,” says Debi Forest, a registered nurse with the University of Florida Health Center in Jacksonville. “There’s a blood test that can be done in the emergency department.”

Forrest agrees that CO detectors are a critical safety feature.

You can’t prevent every CO leak, she says, such as one from a heater that malfunctions without warning. However, “you can buy CO detectors at almost any hardware store,” she says. “These devices can save your life.”

Related: Don’t Let Your Water Heater Get You in Hot Water

Steve Evans, MA, is an award-winning journalist with more than 20 years experience in daily news, investigative, health and business journalism. Among other jobs, he has served as managing editor of the Central Virginia Newspaper Group, as a senior writer for SNL Financial and as a staff writer for The Progress Index and the Richmond Times-Dispatch.