A minor oil spill in the Yard yesterday left students confused about “the rainbow-colored fluid” on the ground and inconvenienced many pedestrians as they walked through the Yard.

After the University’s Environmental Health and Safety (EHS) officials were notified of the spill at 12:20 p.m., hazardous material experts reported to the Yard to evaluate the situation. There, they found less than 5 gallons of hydraulic oil on the pathway between Weld Hall and Widener Library, according to EHS Director Joseph Griffin.

He said the hydraulic oil—a non-flammable, “fairly inert” substance—spilled from a piece of vendor equipment passing through the Yard, but said he was unsure if the equipment was a vehicle or some other piece of machinery.

After surveying the scene, EHS officials brought in hazardous waste specialists to contain the spill and clean up the oil, Griffin said.

“It’s pretty rare. We might see three [such spills] a year. They’re easily contained because the hydraulic oil is in small quantities,” he said.

Though the spill was not dangerous, Griffin said police cordoned off the pathway from Boylston Hall to University Hall that runs behind Weld in an effort to be cautious.

“[Our officials] are trained to recognize and respond even if they don’t know specific details,” he said. “They will take precautionary measures that are conservative.”

Harvard University Police Department (HUPD) officers were stationed along the perimeter of the yellow police tape to prevent students from walking through the oil.

First-years were bewildered by the unusual liquid that appeared in their backyard yesterday.

“I think it was the communists who spilled the oil. They’re kind of sneaky,” quipped Stephen T. Norberg ’06, who came upon the spill while walking back to the Yard from Annenberg Hall.

Todd C. Bartels ’06 said he had left Weld to walk to Annenberg for lunch at 12:30 p.m. when he noticed the spill.

“I started walking to Annenberg and under me there was this rainbow-colored fluid. I thought that it was just gas from [police] cars going through the yard, but then it followed me to Annenberg,” Bartels said.

He said there was a path of oil on the ground extending “a good bit of the way” to Memorial Hall.

But Griffin said the spill was easily contained and did not spread far.

“They put down absorbent pads [to stop the spread]. If a small spill hasn’t penetrated the ground, we scrape it off the surface,” he said.

Three hazardous waste specialists from University contractor Triumvirate, Inc., poured bags of brown granular material similar to kitty litter over the spill and then shoveled the sticky material into large, black containers.

“Often times they will use a special absorbent material. It could be sand. It will suck up any of the free liquids...and bind to the oil,” Griffin said.

Despite the intricate procedures that EHS used to remove the oil, Griffin said there was never any health hazard to Yard residents.

“The hazards are going to be fairly low. It’s a heavy oil, for that reason it doesn’t move freely in the environment,” he said. “It’s not volatile. It’s doesn’t evaporate.”

—Staff writer Hana R. Alberts can be reached at alberts@fas.harvard.edu.