Oxygen candles are used as a backup source of breathable air in an emergency. In addition, they supply an on-demand source of oxygen, utilised in aeroplanes, space stations, and other applications such as safe havens and refuge chambers.
A safe supply of oxygen is critical to support life. We are dependent on oxygen for survival; our bodies consume it to produce energy. If primary oxygen sources are scarce, these generators are on standby, ready to produce a finite amount of oxygen via a chemical reaction.
Oxygen is produced from a thermal, chemical reaction. Oxygen candles house a mixture of sodium chlorate, barium peroxide and iron powder; the oxygen-producing chemical is sodium chlorate.
This chemical reaction requires a significant amount of energy input, hence the need for iron powder. Iron powder burns at a higher temperature around 600°C (1112°F); as it heats the iron becomes very hot and breaks down the sodium chlorate. This reaction produces oxygen, sodium chloride (common salt) and iron oxide through a process known as thermal decomposition.
The initial energy required to start the reaction occurs when a specific initiation mechanism, a brass starter, ignites the iron powder.
2Fe 3O2 -> 2Fe2O3
NaClO3 -> 3O2 NaCl
Oxygen candles produce a lot of heat. Steps must be followed to ensure everyone’s safety, including the use of gloves and a strict no moving policy.
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.
Why Have Oxygen Candles in Refuge Chambers?
Within refuge chambers, oxygen candles are an independent means source of respirable air while preparations for rescue are made. In the rare event the primary and secondary oxygen supplies fail, the candles are a viable backup.
The primary sources of breathable air within a refuge chamber are:
- Compressed Air: Compressed air is simply the atmospheric “air” being pushed through pipelines down to the refuge chamber via a compressor. Before compressed air can be considered suitable for breathing, airborne water particles, dust, oil contaminants, and pollutants such as carbon monoxide and hydrocarbons from diesel exhausts need to be filtered.
- Oxygen Cylinders: Oxygen cylinders reintroduce oxygen into the refuge chamber at the rate it is being consumed. Compressed oxygen is released from a cylinder into the chamber through a regulator that controls the flow rate. Flow is set at the rate of occupant consumption. Oxygen cylinders are used in the event compressed air fails and generally require the support of a scrubbing system to remove carbon dioxide and carbon monoxide from the air.
A candle is an entirely independent source of oxygen from within the refuge chamber. In this way, it’s isolated from common faults found in the other sources:
- Compressed Air: The feed can often be compromised during an emergency due to damage to the circuit or carbon monoxide contamination requiring the chamber to be isolated.
- Oxygen Cylinders: Leaks or tampering of the bottles is possible, impacting the cylinders’ effectiveness. Candles can’t leak or be tampered with without initiating the candle.