The story was also produced in partnership with NBC News.

A congressional committee is investigating whether portable generator manufacturers have done enough to protect the public from deadly levels of carbon monoxide emitted by their products.

Rep. Carolyn B. Maloney, D-N.Y., who leads the House Committee on Oversight and Reform, sent letters to top executives at four major generator companies on Tuesday requesting copies of records documenting why they have not implemented potentially lifesaving safety upgrades in many generator models for sale. Maloney also asked for messages sent or received by officials at the companies — Generac Power Systems, DuroMax Power Equipment, Firman Power Equipment and Champion Power Equipment — related to any injuries or deaths connected to their products.

The committee investigation comes more than two decades after U.S. regulators identified the deadly risks posed by portable generators and six months after an investigation by NBC News, ProPublica and The Texas Tribune found that federal efforts to make portable generators safer have been stymied by a statutory process that empowers manufacturers to regulate themselves. That system has resulted in limited safety upgrades and continued deaths. Maloney repeatedly cited the news outlets’ findings in her letters to company executives.

Portable generators, often used to power critical medical equipment and appliances such as refrigerators and air conditioners during electrical outages, emit enough carbon monoxide to kill within minutes when operated in enclosed spaces or too close to exterior openings. Carbon monoxide deaths caused by generators predictably follow nearly every major power outage caused by extreme weather, which scientists say is becoming more common with climate change. Generators played a role in at least 10 deaths in Texas during the February 2021 winter storm and electric grid failure.

“As families prepare for potential extreme weather during the 2022 hurricane season, they shouldn’t have to worry about whether the products they buy to keep themselves safe are dangerous and potentially life-threatening,” Maloney said in a statement. “Unfortunately, with tragedy after tragedy, we’ve seen that portable generators have become one of the deadliest consumer products on the market.”

Portable generators kill an average of 80 people in the U.S. annually. After years of studying the problem, the Consumer Product Safety Commission concluded that warning labels and manuals instructing users to only operate generators outdoors were not enough to prevent accidental deaths. In 2016, the agency determined that manufacturers could save lives by making machines that emit significantly less carbon monoxide.

Instead, under industry-friendly federal laws, generator makers were allowed in 2018 to propose their own less expensive and voluntary solution: sensors that automatically turn the machines off when carbon monoxide builds up to an unsafe level.

But in the years since, some manufacturers have not added the safety switches or reduced carbon monoxide emissions in many generators for sale, especially in low-budget models, leaving consumers in many instances to choose between cost and safety, the ProPublica, Texas Tribune and NBC News investigation found.

The safety commission echoed those findings in a report issued this year. The 104-page report said automatic shut-off sensors alone, even if manufacturers installed them in every model, could not prevent all carbon monoxide poisonings caused by generators. The best solution, according to the commission’s findings, was to both reduce generator carbon monoxide emissions and add automatic shut-off switches — a comprehensive approach that only a few manufacturers have implemented.

Based on those findings, the commission said its staff would urge the agency’s five commissioners to move forward with a federal rule requiring generator makers to cut carbon monoxide emissions and add safety switches in the next fiscal year, which begins in October.

Maloney cited the safety commission report in her letters Tuesday to the chief executive officers of the four companies. Maloney told each of the CEOs she was concerned that the companies had “failed to adequately implement voluntary standards to reduce the risk of death from CO poisoning,” based on the commission’s report.

The letters said that the four companies had failed to add any safety upgrades to many or most of the generators they listed for sale in the fall of 2021.

“The Committee is seeking to understand why your company has failed to adequately adopt industry-led standards, how your company plans to prevent putting your customers at risk in the future, and whether legislative reform is necessary to protect consumers,” she wrote to each company executive.

Maloney gave the companies until July 12 to turn over information related to the safety of their products, details about the amount of money they have saved by declining to implement changes and their communication with federal regulators. If the companies fail to voluntarily comply, the committee’s chair has the power to issue subpoenas.

Tami Kou, a Generac spokesperson, said that company officials were in the process of reviewing the letter and that they would respond to lawmakers. In an earlier statement to reporters, Kou defended the company’s efforts to protect consumers. Kou told the news organizations that by 2023, all portable generators sold by the company would be equipped with shut-off sensors.

Dennis Trine, CEO of Champion, said in a statement that the company prioritizes the safety and quality of its products and that officials had started compiling the information requested and will provide it to the committee.

“Temporary, emergency power saves lives for people storing hundreds of dollars of Insulin in their refrigerators and people using breathing machines to sleep at night. The list goes on regarding the critical benefits of portable generators,” Trine wrote in an email.

Trine also said portable generators “never” kill users when they are “used correctly as depicted on the product, packaging and owners manual.”

But safety advocates say those instructions aren’t always easy to follow, because the machines usually can’t be operated in rain or snow. And a review of user manuals by the news organizations, which didn’t include Champion’s products, found that they can provide conflicting messages. Some instruction booklets suggest keeping generators a shorter distance from windows or doors than the 20-foot minimum recommended by the safety commission, while others provide more general guidance such as keeping the machines “far away” from homes.

The other two companies did not immediately respond to requests for comment.

Susan Orenga, executive director of the Portable Generator Manufacturers’ Association, the trade group that developed the voluntary shut-off switches standard, told federal regulators that generator makers have been affected by supply chain problems caused by the pandemic, according to the safety commission’s February report.

“It has been difficult to obtain parts, including CO sensors, to move forward any quicker,” Orenga told the agency.

But Marietta Robinson, a commissioner with the Consumer Product Safety Commission from 2013 to 2018, said portable generator manufacturers could have taken such steps years ago. She welcomed the House committee investigation.

“Most portable generator manufacturers have not invested in making their products safer,” Robinson said. “Instead, they have invested heavily in fighting both this technological change and regulations that would require it.”

The Consumer Product Safety Commission previously estimated that reducing generators’ carbon monoxide emissions would add about $115 to the manufacturing cost of most units, which typically sell for $500 to $1,500.

Robinson noted that generator manufacturers have “made many millions of dollars” off of people’s need for their products in the wake of increasingly frequent severe weather events.

“The least they can do is invest the modestly additional amount in making these products safer by significantly reducing their emissions of CO and saving the lives of those using this product,” Robinson said.