Could our most vulnerable citizens be in danger from something many of them use every day? That's the question a Northwest family asked KIRO 7 Consumer Investigator Amy Clancy.

The Davis family contacted Clancy because they were shocked by what was uncovered after a loved one died.

Sharon Davis tells Clancy she and her brother, Jimmie Wilson, "were buddies." Her daughters loved their uncle just as much. Holly Davis remembers how funny he was. Deanna Davis remembers him as lean and strong.

But in 2006, Wilson suffered a stroke, leaving him partially paralyzed. He went to live at a Spokane Valley adult care facility.

As a life-long smoker, the Davis family says Wilson's written care plan required his cigarettes and lighters be locked up, and that he not be allowed to smoke alone.

But according to a lawsuit filed by attorney Gene Davis on behalf of his daughters who are the victim's nieces, in May of 2007, the 63-year old Wilson used his walker to get out on the second-floor deck, where he lit up.

The suit alleges that no one in the home knew anything was wrong until a worker in the basement saw "drops of fire coming down from the deck where Jimmie had gone out to smoke."

"She saw these molten pieces of diaper coming down, flaming pieces," Sharon Davis tells Clancy. "That's hard to take."

Rick Freier was the fire investigator called to the scene that day. He says those "drops of fire" were from Wilson’s disposable adult undergarment which, along with his other clothing, had caught fire and burned.

"I knew plastic was going to do this," Freier says, "just never thought about the diapers."

Freier tells KIRO 7 that the diaper melted, then dripped through the deck. "The undergarment is made of petroleum product. It is a man-made synthetic material that burns with the heat and intensity of flame. Take a pint of gasoline and strap it to you in a solid state. That's what it is."

During his investigation, Freier documented the damage done to the deck. Because all of Wilson's clothing burned to nothing, Freier also took photos of the type of clothes Wilson typically wore, including thin, polyester-blend shirts and sweatpants which Freier says burn very quickly. But he was also curious about the adult undergarment. So Freier conducted a flammability test on the brand of adult diapers Wilson wore.

He did the same test for KIRO 7 Consumer Investigators.

"We'll simulate a drop right here," Freier says as he ignites the same type of adult diaper that Wilson wore. "As I pull it away, I would expect it to self-extinguish. As you can see, I didn’t put it on there for very long at all."

Freier wrote in his report that the diapers, "proved to be very flammable," and that the material "dripped with the same consistency of plastic."

During his demonstration for KIRO-TV, he talked about the material that fell away from the burning diaper, saying "the drips you see there are the drips that I found all over the deck."

Freier concluded that the fire started when an ash from Wilson's cigarette dropped onto his pants; that Wilson stood and moved toward the house. But that the flames were fanned by the wind, allowing the fire to spread to "the vast majority of his clothes." Freier writes: "The intensity of the flames was due to the flammability of the adult diaper" along with Wilson's synthetic clothing. He ruled the fire an accident.

Freier agreed to talk about the incident, because he believes the flammability of the diaper was one of the contributing factors in Jimmie Wilson's death. "I will tell you right now, it would shock everyone," he tells Clancy. "I work in an industry where I learn a lot about fire and how it works. My job is to find the cause of fires, and it shocked me. I'm surprised we don’t get more people getting hurt by this."

Because of Freier's findings, the Davis family has added the manufacturer of the adult undergarment to its lawsuit against the Washington State Department of Social and Health Services and the owners of the Spokane Valley care facility. SCA Personal Care Inc., the maker of the Tena brand, tells KIRO 7, that while it's "saddended to learn of the death of Mr. Wilson" the company "cannot comment on the specifics of the lawsuit."

Meanwhile, Freier and the Davis family hope people who wear adult undergarments will be cautious near flames.

"I don't think people look at them that way," Wilson's niece, Deanna Davis, tells Clancy. "But they certainly should now, based on what we've experienced."

The family would like to see a flammability warning on the adult undergarment’s packaging. But Amy Bellcourt, spokeswoman for SCA says, both "the packaging and manufacturing processes meet all applicable consumer safety and protection regulations."

Fire Investigator Rick Freier also tested the flammability of some baby diapers. He re-tested them when KIRO 7 Consumer Investigators were in Spokane Valley, and came to the following conclusion: "The adult garment, I think, would be definitely a worse product from the stand-point of flammability."

Freier tells KIRO 7 that adult undergarments are typically thinner than the diapers made for babies.

And in his expert opinion, all diapers -- for children and adults -- are more flammable the thinner they are.

The DSHS, which licenses the home where Wilson lived, had no comment about the pending lawsuit.

The lawyer for the owners of the home did not return our e-mail.