Building a Davy Safety Lamp — A Flame That Cannot Light the Firedamp

Deep coal mines breathe out firedamp — methane gas that a single naked flame turns into a killing explosion. For centuries that gas made the richest coal seams death traps. In 1815 the chemist Humphry Davy solved it with an idea of startling simplicity: wrap the lamp's flame in a cage of fine wire gauze.

The gauze works because metal carries heat away extremely fast. A flame touching the mesh loses so much heat to the wires that it cannot survive on the far side, so the fire stays trapped inside the gauze even when the surrounding air is explosive. The miner gets his light; the gas outside stays unlit.

Better still, the lamp warns of danger. In the presence of firedamp the flame inside grows a tall blue cap whose height reveals how much gas is present, and if the air runs short of oxygen the flame sinks and dies. Davy refused to patent his lamp so that it would spread freely and save lives — and it let miners work the gassy seams that fed the Industrial Revolution's endless hunger for coal.