In caves carbon monoxide can build up in enclosed chambers due to the presence of decomposing organic matter. In coal mines incomplete combustion may occur during explosions resulting in the production of afterdamp. The gas is up to 3% CO and may be fatal after just a single breath. Following an explosion in a colliery, adjacent interconnected mines may become dangerous due to the afterdamp leaking from mine to mine. Such an incident followed the Trimdon Grange explosion which killed men in the Kelloe mine.