(CNN) -- Carbon monoxide, a silent killer, is being blamed in the weekend death of a restaurant manager at a Long Island Mall.
Twenty-seven people, including seven first responders, were taken to the hospital.
In another weekend incident, seven people at the Falls Motel in Ogunquit, Maine, were taken to hospitals after complaining of nausea and headaches. Responders found high levels of the deadly gas.
Earlier this month, a carbon monoxide leak at Baltimore hotel sent nine to the hospital. And last year, three people died two months apart in the same North Carolina motel room.
Here's what you need to know about carbon monoxide:
1. It has no odor, color or taste
You wouldn't be able to see or smell it, but it can be very dangerous to your health and even fatal.
In the Long Island incident, police and emergency crews rushed to Walt Whitman Shops in Huntington Station, New York, on Saturday night after reports that a woman had collapsed in the basement of Legal Sea Foods. Once they arrived, they felt dizzy as well and determined that the cause was carbon monoxide poisoning, said police in Suffolk County, New York.
In the Maine incident, readings found 300 parts per million for carbon monoxide. Anything about 35 parts per million is dangerous.
2. If there's a leak, there's a reason to worry
According to the U.S. Environmental Protection Agency, sources of carbon monoxide could include unvented gas space heaters, leaking furnaces or automobile exhaust in garages.
In the Long Island case, investigators found a leak in the flue pipe of the water heater at Legal Sea Foods, a spokesman for the town of Huntington said. The pipe is supposed to carry gas from the water heater to the outside. Instead, the leak in the pipe caused the gas to build up in the basement of the restaurant.
In the Maine incident, a furnace was to blame.
3. It diminishes your ability to absorb oxygen
If there's too much carbon monoxide in the air you're breathing, you can't take in as much oxygen as you need. This can result in serious tissue damage.
In the Legal Sea Foods incident, the manager, Steven Nelson, 55, was found in the restaurant basement and taken to a nearby hospital, where he was pronounced dead.
In the Maine incident, 21 people complained of symptoms and seven were taken to hospitals.
More than 400 Americans die every year from unintentional carbon monoxide poisoning, according to the Centers for Disease Control and Prevention, and it is responsible for more than 20,000 people visiting the emergency room annually.
4. Its symptoms are often mistaken for something else
In circumstances where carbon monoxide problems slowly develop, victims may mistake their symptoms for the flu. When carbon monoxide levels are higher and develop more rapidly, mental confusion can set in rapidly. Victims may lose muscle control and will probably succumb to poisoning if they are not rescued.
"If you're lucky, you'll get the symptoms and realize something is wrong. A lot of times people just fall asleep and don't wake up," said Bob Bernard, a paramedic with Ogunquit Fire Department, who responded to the Maine hotel call.
5. It can be detected
You can take several precautions to prevent carbon monoxide poisoning, according to the Consumer Product Safety Commission. Chief among them is installing a carbon monoxide alarm in the hallway near every area of your home that is used for sleeping.
The Legal Seafood restaurant didn't have a carbon monoxide detector -- because New York law doesn't require them in restaurants; only in places where people sleep, said Huntington town officials.
Said Legal Sea Foods CEO Roger Berkowitz, "We always assume there is something in place but the reality is there isn't anything in place, this is a sad wake up call for everyone."
The Falls Motel in Maine didn't have carbon monoxide detectors in the rooms, authorities said. Maine law requires them.
CNN's Elizabeth Landau and Matthew Stucker contributed to this report