CHICAGO (CBS) — An investigation by the National Institute for Occupational Safety and Health has found a lack of communication – and insufficient equipment – contributed to the deaths of two Chicago firefighters last year.

The report said poor communication and an insufficient number of radios led to the deaths of 47-year-old Edward Stringer and 34-year-old Corey Ankum.

Ankum and Stringer were killed when the roof collapsed on top of them while they were fighting a fire in a vacant building on the South Side last December.

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Only five of the 13 of the firefighters sent in to fight the fire actually had radios–so they were unable to effectively communicate with other firefighters outside, the report said.

And those who did have radios did not properly communicate with supervisors about the conditions they were facing inside the empty, rundown building in the 1700 block of East 75th Street on Dec. 22.

Supervisors also should have had firefighters leave the building once they determined nobody was inside, the report said.

Fifteen other firefighters were injured when the roof collapsed.

CBS 2 earlier reported that the building housed an old laundry business and had been tagged by the city to either be repaired or demolished, but firefighters were never notified.

Weather also played a role. The roof was stacked with snow and hydrants were frozen.

Chicago Fire Department spokesman Larry Langford told WBBM Newsradio the department agrees there could have been better communication and is taking steps to fix the problems.

The Fire Department now requires that firefighters inside a building provide more details to commanders about the situation, Langford told the Chicago Tribune.

One recommendation — providing every firefighter with a radio — won’t be implemented until next year, when a digital radio system will be operational, the Tribune reported.

Tom Ryan, president of Firefighters Union Local 2, agrees there are valid suggestions in the report. But he took issue with one conclusion: that fire supervisors should have ordered all firefighters out the building more quickly. Ankum and Stringer were inside searching for homeless squatters; it turned out there were none.

“Their first and foremost job is to save lives, and that’s what they were doing,” Ryan said. “I will not second-guess them.”