Factory working conditions during the 1800s in the United States (and elsewhere, in many cases) were, in a word, appalling. Long hours, six day work weeks, little pay (sometimes given in "scrip" that could only purchase things from the company), low light, no heating, and poor ventilation. The list goes on.
It was also often dangerous due to reasons mentioned above: overwork, stressful environment, and dim light, often leading to accidents—accidents that were not compensated for and even "cause" for punishment. Many of these workers were women and children. If such conditions weren't bad enough, the buildings, themselves, were often firetraps (a good example being the Triangle Shirtwaist fire in 1911) or generally dangerous due to construction methods (or cutbacks).
These things came to a head in a tragedy that took place on 10 January 1860 in Lawrence, Massachusetts. The Pemberton Company Mill was established in 1853 and manufactured textiles: cotton goods, flannel, shirts. There were some 900 workers there (mostly Irish women) that day in 1860 when the five story structure collapsed, burying around 670 people.
Crews worked throughout the day and into the night to rescue workers buried in the rubble. Then the second part of the tragedy occurred: a lantern being used by one of the crewmen cracked and caused the remains of the building to catch fire, killing many of those still trapped inside. The result of the collapse and conflagration was 88 dead, 270 injured. And the remainder, already suffering from the incident and the loss of friends and coworkers, out of a job during a time in the United States' history when today's concept of "living paycheck to paycheck" would be a luxury for the common worker.
The third part of the tragedy came later. An inquest was held to determine the cause of the collapse. It was found that the building had been built with cast-iron pillars as support which could not bear the load of the structure's brick walls and the heavy machinery inside. It came out that the engineer in charge of the mill's construction, Captain Charles Bigelow, was well aware of that fact all along. And in what seems a sadly common ending to such stories, a jury found it to have been done with "no evidence of criminal intent." No one bore the consequences of the tragedy except for the workers.
Later, the mill was rebuilt.
(Sources: www.ci.sat.tx.us/safd/fdlerner.htm, www.geocities.com/genweblawrence/mills3.html, www.eskimo.com/~recall/bleed/0110.htm; working condition information from Howard Zinn A People's History of the United States 1980, 1999: twentieth anniversary edition and an American History 101 "VCR Semester" lecture on the Madison, WI, PBS affiliate)