Zotikos mutes the History Channel and the crew, all dressed in white pants and shirts, gathers around the table for a nightly ritual. Owens reads a passage from the safety manual: “Hard hats are designed to withstand the impact of a 2.5-pound hammer falling 20 feet. . . .”

It’s a moment of modern occupational safety that belies Congress’s checkered history as a workplace. Workers here tracked the country’s labor struggles, from the slaves who helped build the original structure (the Capitol’s cornerstone was laid by George Washington in 1793) to the New Deal battles over wages and working conditions, protections from which Congress routinely exempted its own workers. As late as the 1980s and 1990s, advocates protested employment conditions in the Capitol, including workers digging through contaminated trash without protective clothing.

Now, amid a push in the District and other cities for a $15 minimum wage, the Architect’s painters, custodians and other workers make $16 to $32 an hour, depending on seniority and skill level. More than a quarter of them are covered by union contracts, and full-time employees receive health insurance, retirement savings plans, transportation subsidies and other benefits. But those who work for contractors, including the companies that run the House and Senate cafeterias, can make far less.

[The homeless man who works in the Senate]

After riding in one of the Capitol complex’s 330 elevators, Owens and Nathan are set up in the Cox Corridors, some of the House wing’s most elaborately decorated passages. Owens, who has been a decorative painter at the Capitol for nine years, begins touching up a stretch of faux marble she had painted 10 days earlier.

Almost 30,000 people work here, the population of Ithaca, N.Y., surging daily through the Capitol complex. The crush of bodies stays well below the ceiling paintings of muralist Allyn Cox, but traffic takes its toll on the lower reaches.

“This is my baby,” Owens says, picking a daub of blue from her little plexiglass palette. “We can’t ever stop.”

Nothing echoes in the corridor now but the painters’ chatter. Nathan forgot his lunch and will be raiding the break-room fridge for day-shift leftovers. Food is a challenge when lunch is at midnight and the cafeterias are closed.

A babble of distant voices passes, a private tour being led by Rep. Lamar Smith (R-Tex.). “We see about one of those a week,” says Nathan, who has been driving in each night from Temple Hills, Md., for 12 years. “When it’s the State of the Union or something, we just stay put in the shop until they clear out.”

Zotikos approaches, his steps loud in the silence. He has walked over from the Capitol Visitor’s Center, where 2 million to 3 million tourists a year congregate, and his crews repaint the walls near the restrooms almost weekly. According to his fitness app, Zotikos logs 4,300 steps a night, almost three miles, zipping along empty corridors to check in on projects.

“It’s easy,” he says, “to move around at night.”