A firefighter surveys the damage as crews from Toppenish, Yakima County and Zillah fire departments respond to a structure fire at Toppenish Public Works in Toppenish, Wash., Wednesday, Aug. 23, 2017. Several city vehicles, two employee vehicles, various tools and one of the department’s buildings were destroyed in the blaze at an estimated $2.4. (SHAWN GUST/Yakima Herald-Republic)

Toppenish’s fire chief knows what fueled the fire that destroyed the city’s public works building last month.

He just doesn’t know exactly what sparked the paint-thinner fumes.

“It’s either from a heat source or a spark from the combustion engine on the sprayer,” said Timothy Smith.

The fire department’s report on the Aug. 23 fire at 8 Buena Way lists “flame/torch used for lighting” as the heat source for the fire. But Smith said that’s because the electronic report form does not give an option for sparks, heat or flame from an unknown source.

A city employee was using paint thinner to clean the self-propelled paint sprayer around 2:40 p.m. when the fumes from the thinner he was using somehow ignited. The walk-behind sprayer was used for painting crosswalks and other street markings, Smith said.

“It should have been cleaned outside, in a well-ventilated area, but it wasn’t” Smith said.

The employee unsuccessfully used a fire extinguisher to fight the fire. The building, parts of which were built in 1904, was totally destroyed, along with five city vehicles and two employee’s vehicles parked next to the building.

Smith said earlier that the building’s lack of fire sprinklers contributed to the fire’s spreading quickly. The building was exempt from building code requirements to have a fire suppression system in place because of its age.

Smith said the sprayer was totally destroyed in the fire, leaving no clue as to whether it had a chain on it to ground it from static electricity.

Damage costs are estimated to be about $2.4 million, counting both the building, equipment and vehicles lost in the fire.