This story originally appeared on Grist and is part of the Climate Desk collaboration.

It was just before dawn as seven bulky men in T-shirts and sweatpants gathered in front of a towering glass building on Lexington Avenue in New York City. Marcelo Crespo, a 41-year-old with gleaming green eyes and a goatee, beckoned the group over to a white company van, handing each man a pile of protective gear: face mask and respirators, full-body coveralls, shoe covers, hard hats, masking tape.

Clutching their bundles, the men entered through the back door of the building, taking the utility elevator up 32 floors to the roof. The day before, they had sealed up the workspace like an enormous Ziploc bag, covering a large section of the roof with protective plastic structures to shield it from the open air. Before passing through the clear sheeting, Crespo rattled the scaffolding, checking its stability. He traced a sign of the cross on his chest and whispered a prayer that God keep them all safe. Warning signs plastered the makeshift walls, boxes, and equipment. Caution. Danger. Authorized personnel only.

It could have been a scene from the movie Outbreak, but the job took place several months before the Covid-19 pandemic gripped Manhattan. With every breath, the men were still risking serious health problems–even death–as a result of the microscopic particles of asbestos swirling in the air.

Asbestos abatement workers were deemed essential long before the pandemic. Property owners are legally required to call abatement teams in to remove asbestos any time there’s construction, renovation, or retrofitting. Across the United States, during the coronavirus pandemic, some asbestos jobs have even accelerated as several cities are taking advantage of the closures of public spaces to schedule renovations. And there’s a lot more of that on the post-coronavirus horizon: New York City’s Climate Mobilization Act, which was passed last spring, includes a mandate that the city’s biggest buildings reduce their overall emissions by 40 percent by 2030 and 80 percent by 2050 by installing new windows, insulation, and other retrofits to become more energy efficient.

But while the timing makes sense for cities, it’s not so great for abatement workers, whose occupational risks make them especially vulnerable to serious complications of Covid-19.

Judging from its physical properties alone, asbestos is useful stuff: The naturally occurring mineral’s long, fibrous crystals absorb sound and resist fire, heat, and electricity. In ancient Greek, the word for “asbestos” means “inextinguishable.” By the late 19th century, businesses in Europe and North America were competing for rights to mine it. Asbestos turned up everywhere: in concrete, bricks, pipes, flooring, roofing, and couches. It was used as insulation in schools, hospitals, and theaters. Asbestos was used as snow on movie sets in the 1930s, blanketing Dorothy in The Wizard of Oz.

As it grew in popularity, doctors noticed that relatively young asbestos miners were short of breath, suffering from a condition called pulmonary fibrosis. When asbestos fibers become airborne, the small, needle-like filaments can enter the body through the lungs and skin, accumulating in internal organs and building up scar tissue over decades. By the time symptoms show up, people might already have permanent lung disease, genetic damage, or cancerous growths.

In the US, around 39,000 workers die every year from asbestos-related diseases. About 3,000 of these deaths are from mesothelioma, a malignant form of cancer linked to asbestos exposure. And it doesn’t take much: “Mesothelioma can occur at relatively low levels of exposure,” said Victor Roggli, a professor of pathology at Duke University.