Excerpts from the ChicagoSunTimes.com:

People blocks away from the Mickelberry Sausage Plant were knocked off their feet when a deadly explosion caused by a gasoline fire leveled the building in the Back of the Yards neighborhood on Feb. 7, 1968. Four firefighters were killed.

On Wednesday — 50 years later — more than 100 Chicago firefighters gathered at the site of the fire to remember their bravery, as well as the lives of five employees of the company who also perished.

Moments before the late afternoon blast, Arthur G. Murray, a 23-year-old accountant, was on the roof of the brick building with several co-workers as firefighters scrambled to get them down ladders. Billowing smoke had forced them to the roof. The blaze was being fed by a gasoline tanker that — after completing a delivery to the sausage plant — began leaking fuel into the building’s basement. When the gas reached the boiler, it ignited.

Murray was standing at the edge of the building’s roof, watching the chaos on the street below with an odd sense of detachment when he heard one firefighter tell another: “We’ve got to get people off this roof because it’s going to blow.”

“And as soon as he said the word ‘blow,’ the building just disintegrated,” Murray recalled Wednesday. “I was blown off the roof,” he said. “I ended up across Halsted Street in a used car parking lot — banged against several automobiles — but I was conscious all the while,” he said.

Firefighter Charles Bottger, 27, Firefighter Thomas Collins, 45, Captain John Fischer, 40, and Firefighter Edward Leifker, 40 were killed.

More than 70 people were injured.

However, the carnage could have been much worse. At the time of the explosion, most factory workers had left for the day. Only a skeleton crew remained — most of whom escaped.

thanks Dan