BOULDER, Colo. -- An investigation into a condo fire that left 50 people in Boulder homeless showed much of the damage could have been prevented.

Fire investigators still don't know what started Friday's blaze, but they know what made it spread so quickly.

Propane tanks used for grills acted like blow torches, accelerating the flames.

Investigators said several people barely escaped with their lives and two firefighters were almost trapped.

Those propane tanks are against fire codes in combustible balconies and decks, but David Lowrey, chief fire marshal for the city of Boulder, said with so many apartments and condos in Boulder, it is difficult to enforce.

"It should serve as a very good reminder,” Lowrey said. “This fire could have been handled with a very small impact, except the propane vented and escalated the fire."

He said the lack of sprinklers in the building also contributed to the damage.

The city’s 1988 sprinkler ordinance went into effect one year after the complex was built.

When the condos are rebuilt, they will be required to have sprinklers.

About 50 people lost their homes in the fire, mostly CU students.

The university is holding a clothing and household goods drive and is helping some students with temporary housing as well as books and computers.