Local Methane Detectors in Underground Coal Mines – DGMS Guidelines, Use, Care & MCQs

🧾 DETAILED NOTES

1️⃣ Introduction

Methane (CH₄) is a highly explosive gas released from coal seams. Its early detection is crucial to prevent fire, explosion, and ignition. Local Methane Detectors (LMDs) are portable or fixed instruments used to measure methane percentage at critical points in underground coal mines. Methane is flammable, explosive (5–15% range), odorless, and lighter than air.

2️⃣ Types of Methane Detectors

Catalytic Type: Measures heat produced during methane oxidation. Requires oxygen for operation.
Infrared (IR) Sensor Type: Highly accurate. Measures absorption of IR light. Works even in oxygen-deficient zones.
Portable Hand-Held LMD (Used by officials, overmen, gas-checkers).
Fixed continuous methane monitoring sensors (Installed at faces, return airways, belt galleries).

3️⃣ Statutory Requirements (DGMS / CMR 2017)

Continuous methane monitoring is essential. Cutting, drilling, blasting must stop if concentration exceeds limits.

Methane Danger Limits:
1.0% – Stop power supply
1.25% – Withdraw persons
2.0% – No one permitted

4️⃣ Use of Local Methane Detector

The detector must be switched ON in fresh air and allowed to warm up. Hold detector near the roof where methane accumulates. Check methane: at face, near machines, return sides, and around goaf edges. MUST check methane before restarting equipment.

5️⃣ Care & Maintenance of LMD

Daily Care: Check battery level, Zero calibration check (in fresh air), Clean probe, Observe display stability.
Weekly Care: Bump test (with methane test gas) to confirm sensor response, Check alarms (visual + audio).
Monthly Care: Full calibration and accuracy verification.
Annual Care: Factory calibration (mandatory), Sensor replacement (as needed).

⚡ QUICK ONE-LINERS (REVISION)

Methane explosive range = 5–15%.
LMD must be switched ON in fresh air.
Check methane near the roof.
1% methane → stop power.
1.25% methane → withdraw persons.
Catalytic LMD requires oxygen.
IR LMD works in oxygen-deficient zones.
Daily zero check is compulsory.
Bump test done weekly.
Calibration required monthly.

🧠 DESCRIPTIVE MODEL ANSWER

Q. Describe the use and care of Local Methane Detectors in underground coal mines.

Answer:
Local Methane Detectors (LMDs) are essential instruments for detecting methane concentration in underground coal mines. They are used by officials to ensure methane levels are within safe limits before permitting work (CMR 2017). The detector must be switched ON in fresh air, allowed to warm up, and checked near the roof where methane accumulates.

Proper care is necessary to maintain accuracy. Daily checks include battery condition, zero setting, and cleanliness. Weekly bump tests and monthly full calibration are mandatory. Annual factory calibration and replacement of faulty detectors are required to prevent unreliable readings, thereby mitigating the risk of methane explosions.

🧮 25 MCQs (Dynamic Options A–E)

Q1. Methane is:

Solution: Methane (CH₄) is a highly flammable, odorless gas and the main explosive hazard in coal mines.

Q2. LMD must be switched ON in:

Solution: Detectors must be initialized in fresh air (0% gas) to set the correct zero baseline.

Q3. Methane accumulates near the:

Solution: Methane is lighter than air (specific gravity 0.55), causing it to rise and accumulate near the roof.

Q4. Catalytic detectors need:

Solution: Catalytic sensors work by oxidizing methane; this chemical reaction requires oxygen to occur.

Q5. Infrared detectors:

Solution: IR sensors measure light absorption, a physical process, meaning they do not require oxygen for chemical reaction.

Q6. Bump test should be done:

Solution: A quick functional check (bump test) with certified test gas is typically required weekly to verify sensor response.

Q7. Methane must be checked before:

Solution: Operating powered equipment (which can cause a spark) is a high-risk activity that must be preceded by a gas check.

Q8. Above 1.25% methane, work must:

Solution: 1.25% is the statutory limit for withdrawing persons, indicating extreme danger.

Q9. Main danger of methane:

Solution: Methane is the primary cause of major fire and explosion disasters in underground coal mines.

Q10. Detector must be stored in:

Solution: LMDs are sensitive electronic instruments and must be protected from moisture and dust for accuracy.

Q11. Weekly care includes:

Solution: A weekly bump test verifies that the sensor and alarms are functioning correctly when exposed to test gas.

Q12. Telemonitoring prevents:

Solution: By providing continuous, real-time data, telemonitoring systems are the best defense against major methane explosions.

Q13. System must warn through:

Solution: An alarm system must provide both audible and visual warnings to ensure the alert is recognized in high-noise/low-light areas.

Q14. Sensor must be kept:

Solution: Dust and debris on the sensor surface can absorb gas or block air flow, leading to inaccurate readings.

Q15. Methane must be checked at:

Solution: The working face is the most likely location for rapid methane liberation.

Q16. Annual care includes:

Solution: Sensors have a limited life and must be replaced periodically (often annually) to ensure reliability.

Q17. Methane should be checked before:

Solution: Gas checks are mandatory before blasting to ensure the blast area is free from explosive concentrations.

Q18. IR detectors measure methane using:

Solution: IR sensors measure how much infrared light the methane gas absorbs.

Q19. Methane explosive range:

Solution: The Lower Explosive Limit (LEL) is around 5%, and the Upper Explosive Limit (UEL) is around 15%.

Q20. Daily check includes:

Solution: A battery check (and zero calibration) is a fundamental daily requirement to ensure the device will function throughout the shift.

Q21. LMD must be kept away from:

Solution: Water ingress can damage the internal electronics and sensor, causing inaccurate or no readings.

Q22. A common use of LMD:

Solution: Gas checking is the specific statutory role of the Local Methane Detector and the designated officials.

Q23. Methane check is essential during:

Solution: Mechanized operations like cutting and drilling increase methane liberation and the risk of ignition.

Q24. Incorrect calibration results in:

Solution: Calibration ensures the device accurately measures the gas concentration; incorrect calibration means the readings will be false.

Q25. Ultimate purpose of telemonitoring:

Solution: The overall goal of fixed monitoring and portable LMDs is ensuring safety in underground operations.

🔗 INTERNAL LINKS

Related Topic	Read More On...
Gas Testing	Gas Testing & Methane Regulations
Mine Ventilation	Mine Ventilation & Gas Control
Intrinsic Safety	Intrinsically Safe Equipment in Mines
Explosion Prevention	Fire & Explosion Prevention in Gassy Mines

🔥 Prepare Smarter with Authentic DGMS Mining Notes & MCQs!

Get DGMS-approved safety notes, diagrams, and MCQs at Online Mining Exam – India’s 1st Mining Learning Platform.

Detailed Gas Testing Procedures
DGMS Danger Limits Explained
5000+ Topic-wise MCQs

🌐 Visit: www.onlineminingexam.com
📞 Call/WhatsApp: 9971114020

Download Methane Detector Notes Now!

Online Mining Exam