It started as a routine call to the D.C. fire department about a mysterious goo-like substance inside a home in the District’s Chevy Chase neighborhood.

Maybe a spilled household cleaner, firefighters first thought.

But the call quickly became serious after the first firefighters arrived at the house on Kanawha Street, just off Connecticut Avenue in Upper Northwest. It wasn’t that the substance — which officials said had been found in a just-opened 40-year-old safe — was particularly dangerous. But no one could identify it

All they knew was it exhibited a chemical reaction to water.

“We took the extra precautions,” said the fire department’s spokesman, Timothy Wilson.

And so a routine call about 4 p.m. quickly became a spectacle, with as many as nine fire trucks, engines, ambulances and a full-blown hazardous material team — men in white space suits — filled the residential street, eventually shutting it down.

The apparatus didn’t leave the street — and the single-family home worth about $770,000 — until close to 3 a.m. The resident could not be reached for comment on Tuesday.

Wilson said that on-scene tests couldn’t identify the substance. Firefighters ruled out explosives and a chemical hazard. But he said they were concerned that whatever it was reacted water. Firefighters wearing protective suits packaged the material and brought to an environmental lab for testing.

“We wanted to be as thorough and careful as possible when we moved it,” Wilson said.