DENVER (CBS4)– Firefighters have completed their onsite investigation at 18th Avenue and Emerson Street. But what caused the fire has not been released to the public.

On Friday, CBS4’s Rick Sallinger gained access behind the perimeter where investigators were combing through the rubble of the 5-story apartment building that was going to be called “Emerson Place.”

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(credit: CBS)

Fire investigators said they are looking into the spray foam insulation used by the construction workers.

PHOTO GALLERY: Fire At Denver Construction Site

Two construction workers were killed in the massive fire that broke out just after noon on Wednesday. One of those victims has been identified as Roberto Flores.

Roberto Flores-Prieto (credit: Facebook)

Six others were injured in the fire.

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“The spray insulation that is used is just that, it’s sprayed and we know, it’s well documented that it’s flammable if it’s not done just the right way,” said Denver Fire Capt. Greg Pixley.

(credit: CBS)

More than 50 construction workers were at the site at midday when the smoke and flames shot into the sky. Workers reported first seeing the fire on the third floor. Some jumped from the second and third floors of the building to escape.

(credit: CBS)

More than 100 firefighters rushed to extinguish the blaze.

Dozens of cars were destroyed along with construction equipment. Nearby homes, apartments and offices were damaged and are uninhabitable.

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Clarification: Denver Fire Captain Greg Pixley contacted CBS4 to say he misspoke when he said the foam insulation was flammable. He says he should have said “combustible.”