It is almost a tradition that mining disasters usually begin as fires, floods, rock-falls, or explosions with the release of smoke and toxic gases blocking escape routes, leaving the miners injured or simply overwhelmed by events. Sometimes a lucky few miners escape to an air pocket and wait for rescue. Today this place of last resort is the refuge chamber, which is rapidly entering service in the USA, Australasia, China and elsewhere. These steel boxes feature a heavy duty construction capable of withstanding overpressures of 15 PSI or more without deformation and comprise a small airlock chamber and a main chamber, housing 8 to 24 miners. Here they are largely protected from secondary blasts, flash fires, with systems that can support life for several days (96 hours), even when cut off from the main air and power supplies.
As might be imagined, conditions inside the chamber could soon become intolerable with each miner generating around 150 watts of heat so the whole team could be generating as much heat as a domestic cooker going full blast, so effective air conditioning is essential. However, the intrinsically safe design removes the potential dangers of electrical equipment igniting coal dust residues or flammable gases, by making the chambers powerless, stand-alone devices. Instead, compressed air from under-floor banks of cylinders is often used to power the air-conditioning units and the CO2 scrubbers, essential to keep this gas down at safe levels.
When cooped up for several days the miners depend upon the knowledge that all is well within the chambers and, even more, they need to know that all is well outside before they risk leaving the safety of their temporary home. This is where real-time gas and environmental monitoring plays an essential part. Often portable gas monitors are pressed into service but the best systems will have a monitor inside the chamber and one in the air-lock connected to remote sensors outside the chamber. The systems typically need to monitor the levels of oxygen, carbon monoxide and dioxide; methane and hydrogen sulphide gases, as well as the environmental conditions of temperature, humidity and pressure. Again, the power supply arrangements need to be intrinsically safe and sufficient to maintain operation for over 100 hours. But most of all, the monitoring needs to be accurate and reliable. For this is one area where skimping on specification could transform a place of sanctuary into a tomb of steel. The data collected by the environmental monitoring system is fed back to a display panel in the refuge chamber in real time, so miners know when it is time to leave their temporary sanctuary.
Answer provided by Stan Curtis, Gas Sensor Guru at Trolex Ltd