Gas Sampling Techniques | Indian Minerology

Deepak Kumar Jogi January 21, 2026

Part 3: Sampling Techniques

Key Learning Objective: Master correct gas sampling methods, frequencies, and documentation as per CMR 2017 Regulation 118-122 and DGMS Tech Circular No. 2 of 2018.

3.1 Types of Gas Sampling Methods

🎯 Direct Sampling

Most Common Method
Real-time digital reading using handheld detectors

Instant results
No sample storage
Statutory compliance

🛍️ Bag/Canister Sampling

Laboratory Analysis
Collect gas for GC-MS testing

Tedlar bags (1-10L)
Aluminized canisters
24-hour samples

📡 Remote Sampling

High-risk areas
Tube/pump extension methods

Up to 30m extension
Split sampling points
Goaf edge monitoring

3.2 Statutory Sampling Frequencies (CMR 2017)

Location	Frequency	Regulation	Instrument
Return Airway	Every 2 hours	CMR 118(1)	Explosimeter
Working Face	Before each operation	CMR 118(2)	Multi-gas detector
Goaf Edge	Hourly during extraction	DGMS Circular	Remote sampler
Intake Airway	Daily	CMR 122	Fixed monitor

3.3 Step-by-Step Direct Sampling Procedure

✅ 7-Step Gas Testing Protocol

Pre-check: Instrument calibration, battery, zero in fresh air
Position: Hold detector 1-2m from roof/rib at breathing zone
Stabilize: Wait 30 seconds for reading stabilization
Record: CH₄%, CO ppm, O₂%, Temp, Location, Time
Multiple points: 3 readings per location (roof, mid, floor)
Action: >1% CH₄ = Stop work, ventilate
Sign off: Gas book entry (Form V-24)

3.4 Gas Collection Techniques

🛍️ Tedlar Bag Method

Volume: 1-3 liters
Material: PVF (Tedlar)
Max storage: 24 hours
Valve type: Dual polypropylene
Lab analysis: GC-FID

🥫 Canister Method

Volume: 1-6 liters
Pressure: 20-30 psi
Storage: 30 days
Material: Electropolished SS
For: NOₓ, VOC analysis

3.5 Common Sampling Errors & Corrections

Error	Cause	Correction
Low CH₄ reading	Detector near fresh air	Sample from stagnant zone
False CO alarm	Sensor cross-sensitivity	H₂S interference check
Bag contamination	Improper purging	Triple N₂ purge