BLACKSBURG, Virginia (CNN) -- Carbon monoxide poisoning remains a danger year-round in the United States, but health officials warn that hurricane season increases that danger.
Residents leave a Blacksburg, Virginia, building where several students were overcome by carbon monoxide.
More than 500 people die accidentally and thousands more are sickened each year from the colorless, odorless gas that's produced when natural gas, gasoline, charcoal or other common fuels are burned. In an area that's enclosed or not ventilated adequately, carbon monoxide can build up and poison the people and animals who breathe it in concentrated amounts.
The poisoning can be the result of faulty appliances or carbon monoxide leaks, as occurred in Blacksburg, Virginia, on Sunday when 23 people at an apartment complex fell ill.
Blacksburg Police said a valve on a water heater that was malfunctioning is thought to be the cause of the incident. Police said the valve was stuck in the open position, causing a constant burn-off of fuel and creating carbon monoxide that was not ventilating.
Five students' conditions have improved after receiving treatment in a hyperbaric chamber, hospital officials said.
As Hurricane Dean swirled toward Mexico after slamming Jamaica, health officials said they see a spike in poisoning incidents after hurricanes and other major storms. The danger comes when electricity is knocked out and people look for other power sources for cooking, lighting and cooling or heating their homes.
"The big contributor is that people have generators and they use them in ways that they think are safe, but they're not," said Dagny Olivares, a health communications specialist at the Centers for Disease Control and Prevention. Olivares pointed to a CDC survey that showed that 10 people died in Texas and Alabama from carbon monoxide poisoning in the days after Hurricanes Katrina and Rita raked the Gulf Coast in 2005, and nearly all of those deaths were the result of gasoline-powered generators.
"We recommend that people don't run a generator even close to the home, basement, garage or near a window," Olivares said. "Put them as far away from the house as you can -- without getting too close to the neighbors'."
Health officials point to the use of charcoal grills, barbecue grills or camp stoves inside the home and the use of gas ranges for heat as other dangerous practices that tend to go up in frequency after storms knock out electricity.
Officials note that besides avoiding those risky practices, the ways to prevent carbon monoxide poisoning are simple: Install detectors in the home, changing the batteries at the same time that you change the smoke detector batteries; and have your fuel-burning appliances -- oil and gas furnaces, gas water heaters, gas ranges, gas dryers, gas or kerosene space heaters, fireplaces, and wood stoves -- inspected annually to ensure they're working properly and that the ventilation is appropriate.
While the death toll from carbon monoxide poisoning is significant, the CDC estimates the total number of unintentional, non-fire-related carbon monoxide poisonings is much higher, resulting in between 15,000 and 40,000 emergency department visits each year in the United States.
The most common symptoms of carbon monoxide sickness are headaches, nausea and confusion. But people who are sleeping or intoxicated can die from the gas without showing any of the symptoms. Health officials stress that people seek prompt medical attention if they suspect carbon monoxide poisoning and feel dizzy, light-headed, or nauseated. E-mail to a friend