DALLAS (CBSDFW.COM) – The death of a Dallas firefighter is under investigation. Chris Pham was found unresponsive Thursday morning at Dallas Fire Rescue Station 49, where he worked.

Apparently, his colleagues tried to revive him, but couldn’t.

Pham was on duty at the station Thursday. A family member said he had gone to his bunk, to take a nap. When his shift ended, around 7 a.m., fellow firefighters went to wake him and found him unresponsive.

At a news conference Thursday afternoon DFR Chief Eddie Burns said, “This morning our hearts are broken, following the loss of our brother Chris Pham. He was a bright and shining star and a future leader in the Dallas Fire Department.”

The flag outside Station 49 now hangs at half-staff, as firefighters mourn Pham’s death. According to family members, the 35-year-old firefighter had no known health problems.

Pham had worked with Dallas Fire Rescue, as an Emergency Medical Technician (EMT) since 2006 and was engaged to his childhood sweetheart, a woman he first met back in 7th grade.

The death has been especially hard for Pham’s friends at Station 49 who performed CPR and rushed him to His to a local hospital, where he died.

There will be an autopsy performed, but so far the Dallas medical Examiner’s Office has not yet determined Pham’s cause of death.

“His desire to serve the citizens of Dallas can only be exceeded by his love for his family, his county, and the fire service,” said Chief Burns.

At least five local, state, and federal agencies are investigating the mysterious death.

Funeral services for Chris Pham are pending.