DENVER — Delta Air Lines has identified what caused a plane to fill with smoke at Denver International Airport on Tuesday night, prompting the evacuation of more than 140 passengers and crew.

The airline says a small amount of hydraulic fluid dripped onto the aircraft’s auxilary power unit. That’s a small jet in the back of the plane. It’s typically activated after a plane lands as a way to generate electricity.

Steve Katich was one of the passengers on the plane. He says smoke or fumes started to fill the cabin just minutes after the plane landed.

“People were starting to cough. Eyes were burning and people really started to hack a little bit. There there was some shouting. People were yelling ‘Let us off. Let us off.’ There was a lot of anxiety about that,” Katich said.

Katich snapped several pictures right when the cabin was just starting to fill with smoke. Within seconds he says it was so thick passengers couldn’t see more than a few rows ahead.

“Then it started to smell. The smell was just intense, just a really nasty smell like burning plastic or burning styrofoam or something that was manufactured,” he said.

The smoke prompted an evacuation on the tarmac. The FAA requires that airlines be able to evacuate a plane in no more than 90 seconds. The evacuation on Tuesday took close to 10 minutes.

Steve Cowell is a former pilot and flight attendant. He says the FAA and a team of inspectors from Delta will evaluate why the evacuation took so long, but he says passengers didn’t help.

Many can be seen on cellphone video exiting the plane with their carry-on luggage.

“It’s just unconscionable, unbelievable after what we’ve seen lately passengers would not pay attention to flight attendants or their instructions,” said Cowell.

Investigators will interview passengers to determine whether flight attendants properly issued instruction, but Katich says the crew was clear.

“They said don’t worry about your carry-ons. Just evacaute,” he said.