Transcript for What to know about carbon monoxide, fire safety this holiday
Reporter: The snow-capped mountains of lake tahoe, California, an idyllic backdrop for a get away. It was just that for Ana Farris, celebrating Thanksgiving with a dozen family members in a vacation rental home until a silent killer crept in. We need a medic to respond. Reporter: On Thanksgiving day, some of Farris' group began to feel eel, suspecting altitude sickness. They go to the hospital diagnosed with something far more dangerous. Carbon monoxide poisoning, everyone still in the house was ordered to get out immediately. It's miraculous that everyone walked away from this incident without significant injury many. Reporter: The carbon monoxide levels were six times higher than normal. The level where you're not going to feel very good and if you fall asleep you're probably not going to wake up. Reporter: The actress tweeting, I'm not quite sure how to express gratitude to the lake tahoe fire department. It's a stupidly traumatic story, but I'm feeling very fortunate. It is often called the invisible killer because you can't see it, smell it or taste it. Reporter: The danger of carbon monoxide poisoning while traveling is something Jamie Williams knows all too well. You can't assume that the place that you're staying in has been protected with a carbon monoxide alarm. Reporter: Back in 2013, she and her 11-year-old son Jeffrey checked into room 225 at the best western in Boone, north Carolina. But that particular room had a deadly secret. My last vision I have of him is just sitting on the edge of the bed. Reporter: Sometime in the night Jeannie wakes up feeling sick. She crawls to the bathroom and realizes she has to call 911, but her phone is in the other room. I remember trying to get to the door and I couldn't. And that's last thing I remember. Reporter: The next morning a hotel employee discovers the mother and son. Two bodies. And I need some help up here, now. The next thing I remember is is waking up in the hospital room. I couldn't talk. I guess that was from being in a coma. Reporter: Her husband has devastating news. Their beloved son Jeffrey has died. But unbelievably, Jeffery wasn't the first victim of that room at that very best western. I said if I'm not mistaken, that's the same room we had the last call at. Reporter: He was the first responder just as he had been seven weeks earlier. I just got in the room. There's two people, neither one are breathing. Neither are breathing? No, ma'am. A retired couple from Washington state had tied from carbon monoxide poisoning in the same hotel room. Another near tragedy just days after the Jenkins' death. The Zelinsky family checked into the room above to celebrate a birthday party with a sleepover and pool party. All the girls were sick, falling off like flies. Reporter: She complained to the front desk. My name was written on a yellow sticky note and I was told the manager would be told. Reporter: But the company who owns the hotel swears they were never told. You were not informed by your employees that people had gotten sick in the room right above 225? I was not. Reporter: It was only after the third incident that first responders finally discovered the toxic source. The pole heater's exhaust pipe was designed to conduct the sar bon monoxide safely outside, but hidden under a drop ceiling directly under 225, state investigators find the pipe is busted, full of holes, propped up by a vhs cassette tape and bucket, spewing poison gas into the rooms above. They never mentioned carbon monoxide. In 2016, the hotel management company pled guilty to three counts of involuntary manslaughter. The hotel in Boone, north Carolina is is now under new ownership. Incredibly, only 15 states have laws or regulations requiring carbon monoxide determinates in hotels. Had I known six years ago they weren't required in hotels I would have had one. Reporter: Of course another source of carbon monoxide, fire. There's always more fires during the winter holidays because of increase use of candles, heating. The major causes of fires ramp up at this time of year. Reporter: How fast a fire can overtake a home is evident in this demonstration we did at the Delaware county training center outside Philadelphia. With the help of ul, the company that sets the safety standards for smoke alarms we constructed a house and lit it on fire. Everything in this room is synthetic, made out of oil. 30, 40 years ago everything might have been naturally made. Now it is going to be much more flammable. Back nat day you had about 17 minutes to get out. Now you have 3. Reporter: Within minutes the temperature hits 400 degrees. The air unbreathable. The lower you are the cooler and cleaner the air is. I'm walking out of here on my knees. Reporter: One of the bedrooms in the house has the door closed, smoke only coming to the room at the top edge of the First thing to do, touch the door, is it hot in is the handle hot? If it is, do not, do not open this door. Teddy bear, pillow, anything that might alert someone you're here, throw that out the one window. Reporter: Outside you can see the difference between the bedroom that had the door closed and the one that did not. It's literally day and night survival and death. You want to have working smoke alarms and carbon monoxide alarms throughout your home. Every level of the home. Inside and outside of the sleeping rooms. Reporter: Jeannie Williams started a foundation to honor her son Jeffrey. Today she's getting ready for an annual fundraiser, a brick-building contest, something Jeffrey loved to do. It's just a fun way to celebrate Jeffrey's light. Reporter: They donate the money to fire departments so they can purchase carbon monoxide detectors to give them out for free to communities. You don't want somebody to go through that when it's preventible. Reporter: For "Nightline," Matt Gutman in Philadelphia.
This transcript has been automatically generated and may not be 100% accurate.