It sounds like something that you'd see in a horror movie: As a deluge of lethal foam engulfs New York City's concrete-and-steel canyons, panicked Manhattanites with nowhere to run can only watch as it approaches, before they finally suffocate.

For countless chickens, turkeys, and ducks trapped on factory farms, that terror is real. It's called "mass emergency depopulation," and it's as hideous as it sounds: Birds who've been exposed to avian influenza are smothered with a blanket of foam similar to the kind that firefighters use to put out oil fires.

With no way to escape, they can only watch helplessly as the suffocating wall of foam engulfs them.

There were 14 outbreaks of avian influenza in the United States last year, from Alabama to Montana. The virus' spread is dangerous to public health, but it's catastrophic for chickens, turkeys and ducks. Because humans lust after their flesh and eggs, the birds are crammed by the thousands into fetid warehouses and sheds, exacerbating the spread of disease and putting humans at greater risk, too. When the birds inevitably contract the flu, they're exterminated.

Foam has been the poultry and egg industries' preferred method of extermination since 2006 when its use was approved by the U.S. Department of Agriculture (USDA) and sanctioned by the American Veterinary Medical Association (AVMA). It obstructs birds' upper respiratory tract, including their windpipe, and is supposed to kill 95 percent of them within seven minutes and an entire flock within 15 minutes.

At a meeting hosted by the USDA to determine whether to approve the killing method, an experimenter who had observed it in action recounted that "[y]ou saw birds' heads sticking out of the foam" as they struggled to escape. Eventually, he said, they were "worn out."

At the meeting, Holly Cheever, a veterinarian who has cared for chickens for more than 30 years, said that there is no way to determine how much birds suffer because they're obscured by the foam and probably unable to vocalize their distress as they're buried. Their immobility as the wall of foam approaches shouldn't be interpreted as a lack of stress or concern, she added.

"Finally," Dr. Cheever said, "a board-certified veterinary toxicologist [stated that] it is likely the chemical ingredients of the foam will cause irritation of the birds' eyes, mucous membranes, and skin."

Dr. Ian Duncan of Canada's University of Guelph summarized the concerns of those who care about birds when he said that "foam is a horribly inhumane way" to kill them.

Despite testimony from experts that suffocating birds with foam causes them prolonged suffering, the poultry and egg industries' desire for a cheap and efficient method of killing sheds full of animals prevailed when the USDA and AVMA rubber-stamped the practice as acceptable.

An advertisement for the foam that appeared not long after it was approved for use went straight to the crux of the matter: "One person can do whole-house depopulation."

There’s simply no humane way to kill tens or hundreds of thousands of birds in these sheds at once. But our food system shouldn't have to get to a point where such mass killing is necessary. We don't need to warehouse birds in such filth that they fall ill and are buried under a blanket of foam because eating meat and eggs is completely unnecessary. By choosing humane vegan foods, we can spare these smart, sensitive beings an agonizing death—and do our own health and well-being a favor at the same time.