Smithsonian carried an article about it in 1983. The incident occurred on January 15, 1919, at lunchtime, in Boston. A tank of molasses intended to be used for alcohol manufacture ruptured, spilling over 2 million gallons of molasses in a wave 15 feet high, travelling at 35 mph. Twenty-one people were killed, some by drowning, but flying debris from crushed and splintered buildings was apparently the most deadly factor.

Boston smelled like molasses, a principle ingredient for Boston baked beans, for years after.

The text of the article has been posted here, on Eric Postpischil's Molasses Disaster Pages. He requests a notice when the page is cited, so here it is:

Edwards Park, “Eric Postpischil's Molasses Disaster Pages, Smithsonian Article,” Eric Postpischil's Domain, 26 January 2004. Available HTTP: edp.org/molpark.htm. Accessed 30 January 2004.

He has other stuff posted there as well. All sticky.

Cheers!
Mary Anne