The River Meuse flows from France through Belgium and the Netherlands before entering the North Sea.
The area in the Meuse Valley where the incident occurred, between the cities of Huy and Liege and centered around the town of Engis, was densely populated and had 27 factories.
This was added to by large numbers of coal and wood heaters burning due to unseasonably cold weather.
The youngest, a 20 year old woman named Louise Dammes, died walking home from a party and may have had undiagnosed asthma that contributed to her death.
[2] Due to a similar (albeit less severe) incident that occurred in a nearby valley in 1911 that killed off many cattle, many farmers in the Meuse Valley fled to the hillside during the first two days of the smog, reducing livestock casualties and likely saving the lives of several farmers as well.