Source: Sudden Death: Boys Fell to Their Doom in S.F.'s Forgotten Disaster
(SF Weekly News)
The first football game between Cal and Stanford was played in 1892. By 1900 the rivalry had intensified so much the match was titled "The Big Game." The site for the Thanksgiving Day 1900 game was Recreation Park in San Francisco, holding 19,000 spectators. Another group of people, mostly kids, climbed atop the nearby Pacific Glass Works building.
Worse yet, fans clambered to the highest accessible point, the 100-foot-long rectangular ventilator rising 4 feet from the apex of the roof. This open-sided structure was supported only by wooden braces — and, ominously, the fans' perch was directly above the hottest portion of the factory. Forty-five feet below the thousands of stamping feet loomed the squat, 30-by-60-foot east furnace. Fifteen tons of molten glass bubbled within at 3,000 degrees Fahrenheit — a temperature on par with a red dwarf star. This was the only furnace in action that day. More observant fans would have noticed the capping atop the chimney behind them glowing red as it emitted a persistent plume of smoke.
What happens next is a horror difficult to imagine. Around 200 people, mostly kids, fell inside the Glass Works building as its ceiling collapsed. Half fell to the floor, sustaining life-threatening injuries, but they were the lucky ones. The other half fell right over the furnace, hitting the furnace top, severing furnace fuel pipes, and igniting the flowing 'fuel.' The SF Weekly article linked above provides more grisly details (as well as expanding on additional issues).
I'm a little late in warning that the story isn't for the squeamish, but I'm more surprised that I had never heard of this incident until today. Judging by the article's language, I guess I'm not the only one.