One woman died in a house fire in Fort Collins, Colo., on Oct. 8, that officials now say was started after oily rags spontaneously combusted, according to CBS Denver.

The rags were used to stain the deck outside the house, and the contractor left the rags underneath the deck. The woman was unable to escape from a bedroom in the two-story home.

Spontaneous combustion or similar chemical reactions cause 1,600 fires a year, according to the National Fire Protection Agency.

Read WFB’s previous reporting on spontaneous combustion to learn how to prevent tragedy on the job site.