“Candles were used to measure the diminishing levels of oxygen. When a candle placed on the floor went out, children were picked up and held at shoulder height. When a candle on a chair went out, then the evacuation of the level began. And if a third candle, positioned at about chin level, began to sputter, then the whole bunker was evacuated, however heavy the attack above.”
―
Antony Beevor,
Berlin: The Downfall 1945