At about 7:50 a.m. on September 22, 1915 during the subway excavation for a new line, a blast of dynamite caused the temporary roadway of wood planking to give way. A trolley loaded with passengers plunged 30 feet into the abyss created by the cave in.
an explosion followed by a massive street collapse threw 7th Avenue into a scene of pandemonium and carnage.
A beer truck minus the driver also fell into the excavation.
The reason more people were not killed was because the street undulated for a few seconds before collapsing which allowed precious time for people on the street to scatter to safety.
The blast which caused the shoring of the street to give way, was initially thought not to be from an unusually large charge of dynamite. The shoring which held up the street was designed to withstand 700 pounds per square foot if the street was loaded to capacity. The weight at the time of the collapse was 1/10 of that. The chief engineer of the construction company C.H. Stengle said, “It’s a puzzle to me. It was the strongest subway shoring ever built in New York, yet it went down like a house of cards.”