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Flammable gases and vapor pose serious health and safety risks. Flammable gases react easily with oxygen to cause combustion and further release of heat energy. The lower threshold for ignition and possibility of back flashes, where a fire moves rapidly from the ignition point to the original chemical source, means that flammable gases have to be handled with extreme caution in the presence of an ignition source, including electrical circuits.1
What makes some gases more flammable than others is the size of the ignition energy. This is the minimum energy required in the presence of the ‘fuel’ (flammable gas) and oxidizing agent for a localized ignition source, such as a spark, to ignite the mixture. This varies from around 0.1 mJ for most hydrocarbon gases to less than a tenth of this for extremely flammable gases such as ethylene (acetylene).2 There is a pressure dependence of the ignition energy, with higher concentrations of most flammable gases meaning an even weaker ignition source is sufficient to cause a fire, and potentially an explosion, if the energy of the reaction can be autocatalytic.3
Examples of frequently used flammable gases include hydrogen, methane, ethylene, and butane. Many of these are common side products in inputs into industrial processes such as petrochemical refinement, mining, chemical synthesis, and waste and wastewater treatment and therefore, ways need to be found of minimizing their fire and explosion risks.
Firstly, areas that contain such gases must be classed as ‘hazardous areas’ and electrical equipment, and potential ignition sources must be cleared specifically for use in such areas, in accordance with the United States Department of Labour Occupational Health and Safety Administration. Gas monitors must also be used to assess the oxygen concentrations (as this is the typical oxidizer present for causing a fire risk) as well as the amounts of potentially flammable gases.4
Strict requirements about the types of equipment that can be used in the potential presence of flammable gases and the criticality of the accuracy of the readings of these types of sensors mean a great deal of care must be taken with choosing the right combination of gas sensors and detectors for dealing with potentially explosive gas mixtures.
There are two main approaches to flammable gas detection, either the use of wall-mounted gas detectors or portable devices. Portable devices offer a much greater deal of flexibility, and given that different hydrocarbon gases have different densities, and may either sink or rise in a room, it can be difficult to select the best installation position for detectors, especially where there a range of gases that may be a risk.
However, portable detectors will typically be battery operated, and therefore the internal sensors must have very low power draw. Sensors also need to be accurate across a range of gas concentrations, as the lower explosion and upper explosion limits (LEL and UEL) differ for each type of gas and any concentration within this range poses an explosion risk.5 Another key requirement is reliability. Given that measurements of gas concentrations need to be taken on a regular basis, preferably with near continuous gas monitoring so leaks and issues can be identified before they are larger enough to cause a problem, sensors which require minimal maintenance and recalibration are preferable to avoid downtime in safety systems.
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MIPEX-04 Flammable Gas Sensors
An attractive alternative to catalytic bead technologies for flammable gas detection are sensors based on non-dispersive infra-red (NDIR) technologies. For this, MIPEX has been one of the world leaders in pushing NDIR sensors to unprecedentedly low levels of power consumption and reliability.6
The MIPEX-04 Flammable Gas Sensor is currently the world’s lowest power NDIR sensor and sets a new flammable gas detection standard with accurate measurement of methane and hydrocarbons.7 It has an average operating current of fewer than 35 microamps, meaning that, in combination with its miniature footprint, it can be installed in portable gas detectors and even unmanned aerial vehicles. As a result, it has found a home in the G7 Blackline Safety monitors, which aim to provide wirelessly-connected networks of safety devices, making it possible to track the geographical spread of gas leaks, along with remote, 24/7 monitoring of gas sites to improve worker and emergency responder safety.8
MIPEX-04 Flammable Gas Sensor
Manufactured to the highest technical standards with a rigorous quality management system (approved by an ISO 9001:2015 certificate), each infrared sensor undergoes exhaustive environmental testing and characterization prior to delivery to the customer. Alongside its careful design based on proprietary multi-patented LED technology, this is part of why the MIPEX-04 is the industry’s first combustible gas sensor to deliver gas detection with high accuracy and 3-year calibration intervals. This also helps to reduce ownership costs associated with maintenance.
The MIPEX-04 gas sensor ensures reliable and accurate detection over a range of concentrations and environmental conditions as it has an embedded microcontroller, ensuring linearized, temperature-compensated digital output. It is capable of measuring up to 100% volume methane concentrations and is inherently poison resistant, with intrinsic safety “ia”, essential for the monitoring of flammable gases. Overall, this means the MIPEX-04 sensor offers the lowest power performance on the market, in a reliable and maintenance-free way that cannot be rivaled by old catalytic bead technologies or other legacy NDIR devices.
References and Further Reading
- Jones, T A, and Walsh, P T. (1988), “Flammable Gas Detection.” Platinum Metals Rev. 32 (2): 50–60
- Kuchta, J M, (1985), A Summary of Combustion Properties of Liquid and Gaseous Compounds, pg 71 - 77
- Costello, R., Hydrocarbon Gas Flammability, (2018), http://rccostello.com/wordpress/process-safety/hydrocarbon-gas-flammability-part-1-3/
- Occupational Health and Safety (2019), https://www.osha.gov/dts/osta/otm/otm_ii/otm_ii_3.html
- Affens, W A., and McLaren, G W. (1972), “Flammability Properties of Hydrocarbon Solutions in Air.” Journal of Chemical and Engineering Data 17 (4): 482–88. https://doi.org/10.1021/je60055a040.
- MIPEX, (2019). https://mipex-tech.com/about/
- MIPEX-04, (2019), https://mipex-tech.com/catalog/mipex-04/
- Blackline Safety (2019), https://www.blacklinesafety.com/g7-connected-safety-moves-beyond-gas-detection