A fire at a Seattle art gallery may have damaged artworks by Pablo Picasso, M.C. Escher, Rembrandt and Francisco Goya.

Seattle Fire Department investigators say the incident was an accident, likely caused by someone who started a fire to keep warm in the alley behind the building, reports the Seattle Times’ Margo Vansynghel. 

Davidson Galleries is located in Seattle’s Pioneer Square neighborhood. According to CNN’s Cheri Mossburg and Brammhi Balarajan, the blaze began in the early morning hours of January 12, when the temperature was in the low 20s.

Fortunately, nobody was inside the three-story gallery when it caught fire, but staffers estimate more than 100 artworks were damaged in the blaze. The building also suffered “significant” damage, mostly from smoke, the gallery reported on Facebook.

Staffers are still assessing the full extent of the damage. Davidson Galleries specializes in artworks on paper—such as woodcuts, etchings and lithographs—and had an estimated 16,000 works worth more than $1 million in its collection at the time of the fire, per the Seattle Times. The oldest works date to the 1400s. 

“Yes, we have insurance, [but] we love what we do, and we love the art,” gallery manager Rebecca McDonald tells the Seattle Times. “That’s what’s breaking our heart. This is irreplaceable artwork.”

The timing was particularly poor, as the gallery had been getting ready to move to a new nearby location. In preparation for the move, many artworks had been removed from storage, which made them especially vulnerable to the blaze, reports ARTnews’ Tessa Solomon.

Some of the pieces were on the floor, where they likely incurred smoke damage. But others were protected by coverings or stashed in drawers, which may have spared them from the smoke.

Firefighters who responded to the scene were “very judicious” about using water once they realized the building housed an art gallery, McDonald tells CNN. In addition, firefighters and community members came together to help gallery staffers move as many pieces as possible to a safer location.

“It’s the wonderful part of the art community, that they come together when there is a need,” Sam Davidson, the gallery’s owner, tells KIRO 7, a local television station.

One of those volunteers was Charles Spitzack, a Seattle artist represented by the gallery. He tells the Seattle Times that his primary concern is the gallery’s future rather than whether his own work was damaged in the blaze.

“Honestly, I don’t really care about my own artwork right now,” he says. “I’m more looking for ways to continue to help and support Davidson moving forward.”