How to set the lower limit percentage for combustible gas detectors?
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If a combustible gas detector is set to a lower limit of 20%, does this refer to 20% of the explosive lower limit of the combustible gases in that environment? Does the lower explosion limit of the surrounding environment need to be set manually? Or was it determined by a detector?
For those new to this field, thank you to the experts for clearing up our doubts!
Manual setting is required; generally, there are two levels of alarm – the first level corresponds to 25% and 50% of the lower explosive limit of the measured flammable gas.
Set by the manufacturer. It’s generally 20% of the lower explosive limit.
Different gases require different settings; for specific parameters, consult the process specifications!
Reply to 5# lmsa613: Assuming the combustible gas is 1,3-butadiene with an explosion lower limit of 1.4, how should the lower limit percentage be set? If we use other flammable gases, after the lower explosive limit changes, does the percentage value of the lower limit also need to be changed? Thank you!
This post was last edited by qidongzhj on 2011-2-22 at 09:33. Reply to 6# polymer_2004: The lower explosive limit should be set at 25% of 1.4%. If it’s a different gas, then adjustments must be made based on the properties of that particular gas.
I found another passage like this: When using an explosion detector, the concentration of combustible gas in the object being tested should be ≤ 20% of the lower explosive limit (on a volume basis; the same applies here)； When using other chemical analysis methods, if the lower explosive limit of the gas or vapor being measured is ≥10%, its concentration should be less than 1% ； When the lower explosive limit is less than 10% and ≥4%, its concentration should be less than 0.5% ； When the lower explosion limit is less than 4% and ≥1%, its concentration should be less than 0.2%. If there are two or more types of mixed combustible gases, the one with the lower lower explosion limit shall prevail. ------------- What we’re discussing here should fall under the scenario of using an explosion tester. It seems that choosing 20% would be better. Therefore, the lower limit can be set at 1.4% × 20% = 0.28%. I’m a bit confused too; I hope Haiyou can continue to correct me
The specifications call for a two-level alarm system: a pre-alarm at 25% of the lower explosive limit of flammable gases, and an actual alarm at 50%. The alarm settings for flammable gas detectors are preset at the factory; however, they can also be adjusted to any value between 0% and 100% if necessary. Since detectors have varying sensitivities to different flammable gases, it is necessary to calibrate them using appropriate standard gases. For 1,3-butadiene, there are no standard gases available; therefore, hydrogen, methane, or propane are typically used for calibration. Should you have any questions, feel free to contact me at guyi_jse@163.com
Reply to 8# qidongzhj: Thank you for your reply, friend. Currently, the value displayed on the instrument connected to the combustible gas detector in the workshop is around 6.5. I assume it isn’t set at 1.4% × 20% = 0.28%. Otherwise, alarms would keep going off during normal production operations. It’s probably set at around 20%; there might be slight variations depending on the type of gas.
Reply to 9# guyi159: Thank you, Haiyou, for your professional reply!