On this day in labor history, the year was 1917.
That was the day as many as 139 workers, mostly women, were killed in an explosion at the Eddystone artillery shell plant, just outside Philadelphia.
The plant, owned by Baldwin Locomotive works, opened in 1916 and produced munitions for the Russian Army.
Baldwin also manufactured Enfield rifles and armored tanks for American forces.
The United States had just entered World War I days before.
Munitions production soared along with the number of new hires.
About 400 women worked in the F building at Eddystone, which was blown to bits.
F building was where powder fuses were manufactured, loaded into artillery shells and then inspected.
On this fateful morning, about 18 tons of black powder ignited, setting off thousands of shrapnel shells.
This caused a series of detonations felt as far as 10 miles away.
The blast blew some workers through the roof.
Others were found nearby in the Delaware River.
Of the dead, 55 were never identified.
Hundreds more survived, and were badly burned or seriously injured.
Immediately, German and then Russian immigrants were scapegoated as responsible for the blast.
The press shrieked in hysteria over alleged sabotage by German agents opposed to U.S. entry into the war.
Others charged that Russian Revolutionaries at odds with the Russian White Army were at fault.
However, a guard testified that in fact there had been problems with electrically powered powder-loading devices that had been malfunctioning for some time.
He claimed the wires must have short-circuited and caused the spark.
One woman worker insisted, as she lay dying that a shell hit the powder and sparked the explosion.
The cause of the explosion remains a mystery to this day.