Hazardous areas
current readings, plot some historical data and has a menu interface for easy change of settings. As it can be used as a stand- alone device, the Guardian NG has a built-in alarm system so that if any gas concentrations exceed a certain range, a built-in alarm can be sounded. Edinburgh Sensors has NDIR devices
suitable for detecting a wide range of gases, including carbon dioxide, carbon monoxide, nitrous oxide, and various refrigerants. The Guardian NG and GasCard are the most versatile of the gas monitors offered, capable of detecting the largest variety of gases and both offer excellent sensitivity, accuracy and rapid response times. For air sampling in challenging
environmental conditions, all of Edinburgh
Sensor’s devices offer pressure and humidity compensated readout across a humidity range of 0 – 95 per cent. The Guardian NG boasts a ± two per cent accuracy over its full detection range, which is 0 – 100 per cent in the case of gases like methane and carbon dioxide. For some air sampling applications, it may be advantageous rather than having static ‘boxed’ devices, designed for installation on walls, to implement the gas monitoring on unmanned aerial vehicles or drones. The Gascard NG is a flexible, lightweight sensor with a sufficiently low power draw that it can be incorporated into such applications.
Edinburgh Sensors
edinburghsensors.com
Methane Detection in Mine Ventilation SySteMS M
ining is big business, with the world’s 50 largest mining companies worth a total of $1 trillion. Worldwide, the mining
industry is responsible for the direct employment of 3.7 million people, with over 150 million indirectly supported by small-scale mining operations. Many other sectors, such as high- tech industry, are also entirely dependent on mined supplies of materials. This article will focus on methane detection solutions in min ventilation systems. There is inherent danger in creating and operating within subterranean tunnels which results in a high mining death rate, over five deaths per day due to mining accidents recorded in China alone. This is a worldwide problem, with high-profile incidents in the last ten years occurring in New Zealand, Russia and the US among others. The most common source of mining accidents, particularly in coals mines, is an explosion of methane gas. Methane is a colourless, odourless gas which is trapped in mines as part of the coal formation process. As coal is formed from compressed plant matter methane is produced as a by-product then, when rocks are excavated, methane is released into the local atmosphere with potential deadly consequences. Methane explosions in mines are the result of
the concentration of a methane leak in a closed environment. If methane reaches a critical concentration in the air, which is between five to 15 per cent it can react with the oxygen to form carbon dioxide, water and heat. This reaction needs a source of ignition to begin. This does not necessarily have to be an open flame, sparks from mining processes, or a high localised temperature (over 600°C) on hot equipment, can be enough to cause an explosion. The pressure wave created by a methane
explosion is often more dangerous than the initial explosion. The waves can displace large amounts of coal dust, spreading highly flammable
Instrumentation Monthly October 2019
particles throughout the air. The dust can ignite as part of a chain reaction, spreading flames along the mining shaft, consuming any available oxygen to further fuel the fire and generating large amounts of toxic gases. Methane release is unavoidable in coal
mines as it is always present. The problem with methane explosions is not just restricted to active mining sites either. Many abandoned mines also leak methane gas, potentially into residential areas where it can still reach high enough concentrations to be at risk of explosion. The risk of methane gas accumulation
in mines means that gas sensing is an essential part of any mining safety network. To reduce the risk of methane build up, ventilation equipment is used in mines to keep methane concentrations below the explosion limit. Sensors can be placed at ventilation exits to
mine, measuring the outgassing of methane to determine that the methane concentration in the mine itself is not close to critical methods. External sensors are also important to monitor the release of methane to the environment surrounding the mine. In order for gas sensing to be an effective
safety measure, the gas sensors used must be able to detect low methane concentrations at a high reliability. One sensor range that is suited to the critical
safety issue of detecting methane outgassed from mines is the Guardian NG series from Edinburgh Sensors. Capable of detecting methane concentrations between 0-1 per cent, these infra-red based sensors are sensitive enough to detect even the smallest of leaks. What makes the Guardian NG series
particularly well-suited to mining applications is they can be easily integrated in to existing ventilation equipment. As the sensor itself is electronic and could generate sparks, it should be situated on the surface of the mine measuring
gas concentrations released from the mine vents. This provides a guarantee that ventilation systems are working and can also be used to monitoring the off-gassing of old mining sites. Infra-red sensors offer some advantages over
the traditional heat of combustion sensors that are typically used for mining applications and are commonly used in other areas where methane detection is required as methane absorbs infra- red light very strongly at characteristic wavelengths. They also offer faster response times and potentially have longer service lives than heat of combustion sensor alternatives. One huge advantage of IR sensors in safety
applications is the fail-safe nature of the technology. If the IR lamp, and therefore the sensor, fails then no signal is received by the detector, which is an equivalent effect to the sensor detecting a high methane concentration. As a result, a full alarm would sound, notifying staff that the sensor has failed and there is a potentially dangerous situation. With its sensitivity and accuracy for methane
detection and short response time of less than 30 seconds from sample injection, the Guardian NG series offers one answer to the critical safety issue of explosion prevention in mining.
edinburghsensors.com
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