"It is with great sadness that I announce [his] passing," Pimlott said, adding that Van Wormer, 47, had died while on assignment in Santa Cruz at 8 p.m. after losing consciousness and despite numerous attempts to revive him.
His wife Jennifer and their two sons were brought to Santa Cruz and have been joined by his parents and his sister, the chief said in the statement.
Pimlott said Van Wormer's brother, Kirk, is also a battalion chief for Cal Fire in the Sonoma Lake-Napa Unit.
"This is a huge loss for Rob's family, his many friends, his Cal Fire family and the fire service as a whole. Please join me in keeping the Van Wormer family in your thoughts during this very difficult time," he said.
No information was available as to memorial services for Van Wormer at the time of this posting.
Chief Pimlott said he was directing all Cal Fire facilities to immediately lower flags to half staff and all uniform personnel to shroud badges until the conclusion of Van Wormer's memorial services.
Van Wormer worked in the Santa Clara County unit of Cal Fire and was a 24-year veteran of the California Department of Forestry and Fire Protection.
Gov. Jerry Brown on Monday expressed sadness at the chief's passing, and ordered flags at the Capitol in Sacramento flown at half-staff.
"We extend our deepest condolences to Rob's family, friends and everyone at Cal Fire during this difficult time," Brown said.
—Bay City News Service contributed to this report