Christie Hemm Klok’s 3-year-old son couldn't get enough of firefighters. He had a toy engine truck, a plastic helmet he wore all the time, and a collection of books showing firefighters dousing fires and saving lives. But most of them were men, and the lack of women bugged Hemm Klok. "There was maybe one female in any of the books," she says, "and she had short hair and maybe a pink shirt on."

Hemm Klok wanted to show her son a more inclusive vision of the world. She began visiting firehouses in San Francisco, where she lives, to photograph female firefighters. Her new book The Women of the SFFD features 45 portraits of women who spend their days running into burning buildings. “I want to raise a son who thinks he can be whatever he wants—and so can everybody else," she says.

More than 270 women serve in the San Francisco Fire Department, which services 1.5 million people across the city's 49 square miles. They make up roughly 16 percent of the force, compared to just half of one percent of the New York City Fire Department. The numbers don’t necessarily speak to the city’s open-mindedness, though. Oh sure, the fire department made a couple women honorary members in the 19th century (including a pretty opera singer who never picked up a hose). But it didn't allow women to apply for a job before 1976—and it didn't hire any until 1987, when a federal judge forced it to. Current chief Joanne Hayes-White became the first female to fill the role in 2004. “Now it’s not crazy for a woman to be a firefighter in San Francisco,” Hemm Klok says. “They’re on, like, every truck.”

Hemm Klok started noticing the women on fire trucks after moving to San Francisco in 2015 to work at WIRED. She left the company in 2016, and began the series later that year, showing up at firehouses with her Canon 5D Mark IV and a portable light kit and inviting the women to pose for a portrait. More often than not, they'd get called away to fight a fire before she could snap their photo. “I can’t tell you how many times I was just sitting alone in the garage of a firehouse,” she says. Eventually, she began showing up early in the morning, after the women had finished their 24-hour shifts. And when she didn't have childcare, she brought her son. "The firefighters spoiled him like crazy," she says. "They even sent a firetruck to our house during his fourth birthday."

Photographing them challenged some of Hemm Klok's own misconceptions about the type of person who becomes a firefighter. Many of the women had worked in food service or education and only wandered into firefighting after hearing about it from a friend or attending a job fair. “When I thought about people becoming firefighters, I assumed it was something they always wanted to do, to save lives, be brave,” Hemm Klok says. “But a lot of times people come into it later in life."

Her portraits depict the women posing in the firehouses' offices, garages and locker rooms, still wearing their black turnout coats and helmets after a hard day on the job. They're refreshing.“We hear that representation matters all the time, and it really does,” Hemm Klok says. “It’s so reassuring to see yourself not left out of things.”