If you happen to be trapped in a mine with a busted ventilation system, an oxygen candle could save your life. The candles contain sodium chlorate, barium peroxide, and iron powder. When ignited, the iron powder burns at 1112°F which breaks down the sodium chlorate into breathable oxygen and sodium chloride (common salt).
From MineARC systems, which sells oxygen candles:
The candle supplied by MineARC Systems burns for approximately 60-90 minutes, producing 2600L of oxygen. This amount can provide approximately 20 hours of breathable air for four people. An oxygen candle cannot have its oxygen production regulated or halted and once ignited; it produces oxygen at a rate of approximately 28 Litres per minute until it is exhausted.
[via Hacker News]