It was one of the deadliest explosions in Chicago history and it happened exactly 50 years ago today.
Nine people were killed, including four Chicago firefighters.
It was February 7th, 1968. A fire broke out in the Mickelberry Food Factory at 49th and Halsted, which produced sausages and other meat products.
Chicago firefighters begin battling the blaze when a massive explosion rocked the building. Four firefighters and five employees were killed.
On Wednesday, a solemn ceremony was held in an empty lot in the Back of the Yards neighborhood to mark a half century since the tragedy. Politicians, firemen and family members of the victims gathered to remember those whose lives were cut short.
"In the firehouses whenever the bell rings, we always know what seems routine can turn in a split second. And that is exactly what happened 50 years ago,” said fire commissioner Jose Santiago.
The investigation found a gas truck parked in the alley behind the building inadvertently dumped thousands of gallons of fuel into the basement of the factory, and a flame from the building's boiler triggered the massive explosion.
In addition to the deaths, 77 people were injured and more than 300 firefighters responded to the disaster.
The factory building that was at the corner of 49th and Halsted is now long gone. But the memories of what happened here remain fresh in the minds of many.
"The passage of time has not diminished the horrific memories of that awful day,” said Alderman Ed Burke. "In devastation that according to one published account resembled a wartime battlefield."
Firefighters hung a large American flag over today's ceremony, which ended with family members placing a wreath in the snow.
The owner of the factory survived the blast, but died when he rushed back into the building to try and save a disabled employee.