To Michelle Seifer, the timing was just a coincidence: after losing power in a summer storm, she came down with flu-like symptoms. It wasn't until two days later, when a carbon monoxide detector activated and a utility company worker tested levels in her home, that she learned she was being poisoned by the portable generator she had been running in her open garage.

"That's when I went to the hospital and learned that my levels were high enough where they needed to admit me," said Seifer, a finance manager and mother of five in Hartland, Mich. "Because if I didn't receive the proper treatment for the carbon monoxide poisoning, if I were to fall asleep I wouldn't wake up."

It took two days of oxygen therapy for Seifer's levels to normalize, and several months for other aspects of her life to follow suit. She experienced confusion, dizziness, and vertigo, and missed days of work when her symptoms were bad. She said it is not uncommon for people to live with long-term effects from a single instance of carbon monoxide poisoning, which is like "silently suffocating to death."

At certain levels, just five minutes of carbon monoxide exposure is enough to be fatal. The colorless, odorless gas is produced wherever fuel is burned, and can build to deadly levels especially quickly in enclosed spaces. Portable generators, whose engines each emit as much carbon monoxide as approximately 450 cars, are especially common culprits.

Seifer said she is blessed that she happened to be home alone that weekend, and credits the utility company employee with saving her life by telling her to get checked out. But hundreds of others across the country are not as fortunate.

More than 900 people died of carbon monoxide poisoning from portable generators between 2005 and 2017, according to the Consumer Product Safety Commission. CPSC data also indicates that an estimated 15,400 people were treated in emergency rooms for portable generator-related carbon monoxide poisoning during that period.

Silent, invisible, deadly

"As far as carbon monoxide goes, that's a problem that affects persons of all ages ... tragically often," said toxicologist Fred Henretig. "We call it 'the silent killer.'"

Henretig recently retired from clinical practice as an emergency physician, but still works as a senior toxicologist at the Poison Control Center at the Children's Hospital of Philadelphia, which he helped found in 1985. He and his colleagues have been trying to raise awareness about proper portable generator use for years, but carbon monoxide poisoning cases inevitably surge after each big storm. When the power goes out, people turn to their portable generators, and they don't always use them safely.

"So what people tend to do — not always but it's not unheard of — is just set it up like right next to the open garage door and they think, 'OK, that's going to work fine, it will blow out,'" Henretig explained. "The exhaust will blow out, but the trouble is, you can't always account for different drafts and how things get vented around."

That's exactly what happened to Seifer, whose family had been running their portable generator in the garage for years, including during a severe storm just a few weeks before her poisoning. She said they had heard not to run generators in enclosed spaces, but thought keeping the doors open would protect them. When she told friends and family about her experience, they were shocked.

"So many people were not aware that having a generator running in a garage wasn't safe," Seifer said. "I think a lot of peoples' eyes opened ... knowing that they weren't being safe and just how much having detectors can save lives."

But Henretig and others say the problem is bigger than user error — industry regulations, and manufacturers themselves, could make portable generators a lot safer.

Both a solution and a risk

Portable generator sales peaked in 1999, thanks to pre-Y2K anxieties. Demand remains high two decades later, fluctuating yearly based on weather-related power outages. The global portable generator market size was valued at $3.7 billion in 2018.

Portable generators can provide homes with electricity and heat, which is why they are particularly popular during hurricane season and in cold winter months. Demand increased significantly this year in California, where Pacific Gas and Electric is using planned power shut-offs as a wildfire prevention tactic.

Portable generators differ from standby generators, which are permanently installed, weatherproof, and turn on automatically in the case of a power outage. Consumer Reports says portable generators range in price from $400 to $1,500, while home standby generators run from $2,000 to $5,000 before installation costs.

Generators can provide life-saving power in emergency situations, especially for t hose who rely on medical devices that require electricity. But they can also pose serious risks.

CPSC Press Secretary Patty Davis wrote in an email to NPR that portable generators can cause fires, electrocutions, contact burns, and carbon monoxide poisoning, and that the latter causes "by far the greatest numbers of deaths," approximately 75 deaths annually in recent years.

Research suggests carbon monoxide poisoning from portable generators actually has the potential to take more lives than the natural disasters that prompt people to use them. A study tracking confirmed deaths related to Hurricane Irma in Florida, Georgia and North Carolina attributed 16 fatalities to carbon monoxide poisoning and 11 to the storm itself.

In fact, it was a spike in carbon monoxide poisoning cases following Hurricane Sandy in 2012 that spurred Henretig and his colleagues into further action. After seeing what he recalls as 40 or 50 cases in just over a month, he got on the phone with colleagues in New York and other nearby states and discovered they were all seeing the same thing. He wrote to his representatives in Congress, and contacted the Centers for Disease Control.

"You realize this is ... literally a public health epidemic, and we really need to do something about it," Henretig said he told them.

Proper use vs. product safety

Federal agencies like the CPSC and CDC offer guidance about proper portable generator use. They advise consumers to only operate portable generators outside, and keep them at least 20 feet away from the home, facing away from all structures. They urge installing battery-operated carbon monoxide alarms near every sleeping area and testing them frequently.

And in 2007, the CPSC passed a rule requiring portable generator manufacturers to warn consumers about carbon monoxide through mandatory labels with pictograms and phrases like "Using a generator indoors CAN KILL YOU IN MINUTES" and "NEVER use inside a home or garage, EVEN IF doors and windows are open."

But these warnings alone aren't always enough to prevent user error.

Only 15 of the 526 carbon monoxide deaths caused by portable generators in homes between 2004 and 2013 resulted from machines being used outside. In most of these fatalities, the generators were being used in an indoor basement, garage, or "non-basement living space."

Warnings about carbon monoxide exposure from portable generators are mostly local and seasonal. Seifer said she had read articles over the years about families in her county who had died from carbon monoxide poisoning, but hadn't encountered any public service announcements about the dangers of exposure from portable generators.

Issues also arise from the fact that portable generators are not meant to be used in the rain, but are most commonly needed in response to weather-related power outages. People may also prefer to keep their generators inside or close to their homes to prevent potential theft.

Henretig said that while it is important for people to use their portable generators properly, the best possible scenario would be safer machines that prevent user error in the first place.

CPSC documents describe a " hierarchy of approaches to control hazards," in which warnings about product dangers are, perhaps unsurprisingly, less effective than designing-out the hazard or protecting consumers from it. Communications like warning labels and PSAs, they explained, are 'last resort' measures that should ideally be deployed not on their own but alongside efforts to make the products themselves safer.

Safer models, separate standards

Some portable generator manufacturers have begun producing models with automatic shutoff valves for when carbon monoxide reaches a certain threshold in an enclosed space and, in some instances, models with lower carbon monoxide emissions in general.

Portable generators with these safety features first entered the market in the fall of 2018, and experts at Consumer Reports predict seeing more in the coming years.

Seifer's family owns one of these new models, but she didn't know at the time that the shutoff feature was intentional. She said she thought she was using bad gas, and would go down to the garage after about half an hour to restart the generator. In retrospect, she is grateful for the automatic shutoff.

"If it had been an older model it would have kept running, and it's possible that the fact it kept shutting down limited my exposure and is the reason I'm alive today," Seifer said.

Consumer Reports revised its portable generator ratings in August 2019 to recommend just three of 20 models on the market, highlighting only the ones with these new safety features and reversing the status of the 14 previously recommended models that lack this technology.

Two separate voluntary standards govern portable generators. One was created by the Portable Generator Manufacturers' Association, a trade group, and one comes from global safety certification company UL. Each standard has a different threshold for prompting an automatic shutoff, and the UL standard also requires engines to produce lower emissions overall.

Some safety advocates believe one mandatory rule would be easier to follow and enforce than two voluntary standards. The CPSC isn't yet convinced.

"Generally, a mandatory standard provides a uniform, enforceable standard for all to follow," Davis wrote. "A drawback to mandatory standards is that they cannot be revised and updated as easily as a voluntary standard."

She added that the body currently "has rulemaking underway" on a mandatory standard for portable generators, and is evaluating the current voluntary standards as part of that process.

Davis explained that per the Consumer Product Safety Act, the CPSC must first determine that the existing voluntary standard is unlikely to "eliminate or adequately reduce the risk of injury" or that "substantial compliance" with a voluntary standard is unlikely before it can create rules like a portable generator standard.

And industry players don't necessarily want a mandatory standard. The PGMA, whose members include major industry manufacturers in North America, said in a 2014 letter to the CPSC that it was "not appropriate" for them to establish a working group on the issue.

Looking ahead

Progress towards mandatory regulations has been gradual, even as carbon monoxide deaths from portable generators remain steady. Still, changes may be on the horizon.

The Nicholas and Zachary Burt Carbon Monoxide Poisoning Prevention Act was passed by the House in September 2019. The bill is named after two young brothers from Minnesota who died from carbon monoxide poisoning due to a faulty home furnace in 1996, and would allocate funds and authorize the CPSC to help states with carbon monoxide installation and other prevention activities. It has failed to fully make its way through Congress each year since its initial introduction in 2012.

The CPSC voted 4-1 in 2016 to approve what it calls a "notice of proposed rulemaking" that would force manufacturers to lower portable generators' carbon monoxide emissions. But its leadership and composition have since evolved.

When asked how the CPSC's regulatory priorities may change under new leadership, Davis said it is "engaged in an ongoing effort to address CO poisonings of consumers from portable generators." The body plans to release results of what it called a "landmark survey" of the number of smoke and carbon monoxide alarms in homes nationwide at the end of 2020.

For now, Henretig has some recommendations for improving portable generator safety.

He suggested manufacturers make the cords on portable generators at least 20 feet long, with legible warning labels that tell consumers not to place them any closer to their homes than the length of the cord.

"[That] still requires some act ... on the part of the consumer but at least it would kind of hit them over the head that "Oh they gave me a giant cord, you know I guess I should use that,'" he said.

Henretig also recommended chain stores and hardware stores stock their carbon monoxide detectors next to the portable generators. After spending $1,000 on a generator, he said, an extra $20 is an especially small price to pay for a potentially life-saving device.

After her scary ordeal, Seifer wants people to know they should always get checked out when exposed to the gas, no matter how briefly. She emphasized the importance of testing carbon monoxide detectors frequently and replacing them once they are activated, since they stop being functional.

She has since written to the utility company to thank them, and has been sharing her story on social media in the hopes that others will take the precautions she did not.

"That would be the last thing that I would want to happen to somebody," Seifer said. "Just because they thought they were safe and they weren't."

Rachel Treisman is an intern on NPR's National Desk.

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