Gas monitoring is an essential aspect of maintaining a life-supporting atmosphere within a refuge chamber.
Why is it essential to monitor gas levels in a sealed refuge chamber and how is this done? During entrapment, occupants consume oxygen (O2) and expire carbon dioxide (CO2) and carbon monoxide (CO) as part of their normal respiration. CO can also enter the chamber during occupant entry and if the compressed air intake is compromised. As a result, Internal gases need to be monitored by a digital gas monitoring system or manual gas sampling.
A refuge chamber is essentially an airtight box that restricts natural air from entering the internal atmosphere. Without adequate oxygen occupants would quickly suffocate. Rough calculations show this could occur within 2-3 hours. A build-up of CO and CO2 can also poison the air causing a number of serious symptoms and eventually even death. CO has been referred to as the “Silent Killer” because CO poisoning is the most common type of fatal air poisoning.
Gas monitoring is, therefore, an essential aspect of maintaining a life-supporting atmosphere within the refuge chamber. MineARC Refuge Chambers are equipped with Fixed Digital Gas Monitors and manual Gas Sampling Tubes so occupants can monitor the internal atmosphere and take all corrective measures, such as commencing CO and CO2chemical scrubbing or adjusting the oxygen cylinder regulator, to stay alive during an emergency entrapment.
Aura-FX Digital Gas Monitoring System
MineARC’s new Aura-FX Digital Gas Monitoring System is a proprietary fixed gas monitoring unit, designed specifically for use in MineARC Refuge Chambers to provide a more convenient solution to internal refuge gas monitoring.
Aura-FX measures O2, CO and CO2 gas concentrations as standard and has the ability to individually monitor up to 11 gases if required, including Hydrogen Sulfide (H2S), Methane (CH4) and Ammonia (NH3). Aura-FX is also fitted with an environment sensor that measures ambient temperature (-40 to 85°C), internal pressure (300 to 1,100HPa), and relative humidity (0 to 100%RH).
All measurements and trends are displayed on a series of user-friendly, digital screens. Audible voice alarms with procedural instructions will prompt occupants to replace scrubbing chemicals or adjust oxygen supply levels in the refuge chamber as required.
Aura-FX is standard on all new MineARC Refuge Chambers. It is also available to retrofit to most existing chambers during an upgrade or refurbishment.
When utilised as part of the MineARC System Intelligence network, Aura-FX provides real-time gas monitoring data and analysis of the overall internal environment of the refuge chamber via the GuardIAN dashboard.
Oxygen Gas Monitor
Oxygen is the most important gas for sustaining life. Our bodies are dependent on oxygen for survival; it is consumed by our bodies in order to produce energy. Loss of consciousness occurs very quickly without an adequate oxygen supply.
Given that a refuge chamber is a sealed environment, it is vitally important to consider how oxygen levels inside a refuge chamber are managed. Oxygen levels of the “dead air space” will quickly be consumed, and scrubbing of CO2and CO does not replace the consumed oxygen in an occupied chamber environment. Oxygen will, therefore, need to be continually replenished over the duration of entrapment. The sources of breathable air to a refuge chamber include compressed mine air, medical grade oxygen cylinders and as a last resort, an oxygen candle.
The Aura-FX Oxygen (O2) Gas Monitor measures ambient air oxygen levels within the refuge chamber to ensure the internal environment is maintained between 19 and 23% oxygen – vital for the life support of occupants during an emergency situation. With an accuracy variance of within only 2% of the reading, the O2 Gas Monitor uses a method known as luminescence; measuring changes in the fluorescence of a special dye within the sensor. The dye is optically excited by an LED light source, emitting light at a rate that changes with the level of oxygen in the air. The O2Gas Monitor sensor then interprets this as a percentage level.
Due to the fact that the gas detection and monitoring are based on optical measurement, no consumable substance is used. Other advantages of this method include high accuracy, fast response and low cross-sensitivity to other gases.
Carbon Monoxide Monitor
Carbon Monoxide is a toxic gas commonly produced by incomplete combustion and can have severe irreversible health impacts at a comparatively low concentration level of above 35ppm.
The Aura-FX Carbon Monoxide (CO) Monitor is an electrochemical gas sensor that measures the concentration of CO by oxidising it at an electrode and then measuring the resulting current.
To reduce cross-sensitivity to other combustible gases, it has chemical filters for Hydrogen Sulfide (H2S), Nitrogen Dioxide (NO2), Nitric Oxide (NO) and Sulfur Dioxide (SO2).
The CO Monitor has an accuracy level of within just 4ppm within the reading and a sensor range between 0 and 5,000ppm. MineARC recommends keeping carbon monoxide levels in the refuge chamber below 30ppm.
Carbon Dioxide Monitor
The Aura-FX Carbon Dioxide (CO2) Monitor measures CO2 levels in the refuge chamber; ensuring it remains at a safe level of below 10,000ppm. Carbon dioxide is exhaled by chamber occupants as a product of respiration, and it needs to be removed from the air using the refuge chamber scrubbing system. This monitor helps to determine when CO2 chemical change-out is required.
The CO2 Monitor features a non-dispersive infrared (NDIR) sensor. Measurement is based on the physical property that CO2 molecules absorb infrared light or particular wavelengths.
By shining light through the target gas and using suitable optical filters, the light detector will give an output that can be converted into a CO2 concentration value.
The sensor provides a long, stable operation life. Major advantages of this method of CO2 detection include eliminated the risk of sensor ‘burn-out’ if exposed to high gas concentrations and low cross-sensitivity to other gases.
Manual Gas Sampling in a Refuge Chamber
Manual gas detectors can also be used to monitor gas levels in occupied refuge chambers. They utilise pre-filled chemical tubes that react to air being drawn through the hand-held pump device to test the levels of O2, CO and CO2. It is recommended that gas levels are tested every hour and corrective actions made as required. The specified sampling time for O2 is approximately 1 minute, CO2 approximately 2 minutes and CO approximately 4 minutes.