On 9 July 1872 the Tradeston Flour Mills, in Glasgow, Scotland, exploded. Eighteen people died, and at least sixteen were injured. An investigation suggested that the explosion was caused by the grain feed to a pair of millstones stopping, causing them to rub against each other, resulting in a spark or fire igniting the grain dust in the air. That fire was then drawn by a fan into an "exhaust box" designed to collect grain dust, which then ignited, causing a second explosion which destroyed the building. At the time, there were general concerns about similar incidents worldwide, so the incident and investigation were widely reported across the world.