WASHINGTON — Nearly 1 million chickens and turkeys are unintentionally boiled alive each year in U.S. slaughterhouses, often because fast-moving lines fail to kill the birds before they are dropped into scalding water, Agriculture Department records show.

Now the USDA is finalizing a proposal that will allow poultry companies to accelerate their processing lines, with the aim of removing pathogens from the food supply and making plants more efficient. But that would also make the problem of inhumane treatment worse, according to government inspectors and experts in poultry slaughter.

USDA inspectors assigned to the plants say much of the cruel treatment they witness is tied to the rapid pace at which employees work, flipping live birds upside down and shackling their legs. If the birds are not properly secured, they might elude the automated blade and remain alive when they enter the scalder.

Over the past five years, an annual average of 825,000 chickens and 18,000 turkeys died this way, USDA public reports show, representing less than 1 percent of the total processed. Government inspectors assigned to the plants document these kills, which are easily spotted because the birds’ skin becomes discolored.

“One of the greatest risks for inhumane treatment is line speed. You can’t always stop the abuse at these speeds,” said Mohan Raj, a British-based poultry-slaughter expert who helps advise the European Food Safety Authority. “It’s so fast, you blink and the bird has moved away from you.”

The proposal being finalized by the USDA would revamp inspections in poultry plants and increase the maximum line speed – to 175 birds per minute from 140 in chicken plants and to 55 per minute from 45 in turkey plants.

USDA officials stress that the new system could reduce food-borne pathogens.