In stoic and composed testimony, a firefighter who was on scene during the "Black Sunday" tragedy spoke Tuesday about the frantic moments that led to two peers being killed in 2005.

Firefighter Jeffrey Cool told jurors about the conditions FDNY personnel met when they responded to a blaze at a building on East 178th Street. Cool, testifying at the Bronx Hall of Justice, says it was "hell" and that thick black smoke left him unaware of his surroundings.

Cool says he was perched outside a window on the building's fourth floor, from which firefighters John Bellew, 37 and Lt. Curtis Meyran, 46, jumped to their deaths.

According to Cool, the heat had become unbearable. Then, aided by another firefighter, he used a safety rope to temper his fall but ultimately fell 40 feet and survived.

Cesar Rios, the building's landlord, Rafael Castillo and Caridad Coste are charged with manslaughter for allegedly contributing to the deaths of Meyran and Bellow by building illegal partitions in the building.