Deep mines increasingly rely on narrow coal pillars (typically 5–10 m) instead of wide pillars (20–40 m) to reduce stress on underlying seams and raise recovery. That layout, however, raises the risk of coupled gas explosion and coal spontaneous combustion in adjacent goafs. Tang et al. (2019), Process Safety and Environmental Protection, combine field and laboratory work at Yangquan No. 1 coal mine to explain the disaster mechanism and divide pillars and goafs into Safe, General, and Dangerous zones for cost-effective prevention. Below is a structured reading note—not a substitute for the full paper.

Link note: The valid ScienceDirect PII is S0957582019306688 (not …319688). This post covers that paper; slug: narrow-pillar-composite-disaster-classification.

Paper highlights

  • Composite gas + spontaneous combustion hazards are frequent in deep mining;
  • Internal pillar fracturing under stress reduces gas isolation;
  • Disasters arise from cross-pillar gas exchange (CH₄ into roadway / O₂ into goaf);
  • Gas concentration + safety principles guide dangerous-area zoning.

1. Problem background

1.1 Why composite disasters matter

In deep mining, high gas pressure/content and ground stress increase outburst and explosion frequency. Fractures and elevated temperatures also raise spontaneous combustion risk. Spontaneous combustion igniting explosive gas mixtures has become a common pattern in severe coal mine accidents.

1.2 Narrow vs. wide pillars

| Type | Typical width | Intent | Composite-hazard trade-off | |------|---------------|--------|----------------------------| | Wide pillar | 20–40 m | Strong isolation/support | Lower recovery | | Narrow pillar | 5–10 m | Reduce underlying-seam stress, raise recovery | More fractures, weaker gas barrier |

Narrow pillars fracture more under stress, weakening isolation between roadway and goaf:

  • CH₄ can migrate from the goaf into the roadway and exceed safety limits;
  • O₂ can leak from the roadway into the goaf and oxidize residual coal.

Without targeted measures, spontaneous combustion and gas explosion can chain together.

1.3 Gap in prior practice

Grout reinforcement and fire-extinguishing spray are known to improve pillar strength and gas impermeability, but uniform grouting along entire pillars often wastes material in low-risk sections while under-treating high-risk zones. The paper addresses where to focus prevention.

2. Study site

Field work was done at the 81,303 working face, Yangquan Coal Industry Group No. 1 mine (Qinshui Coalfield):

  • Main seam: No. 15, thickness about 4.77–9.03 m (avg. 6.91 m), complex partings;
  • Overburden: porous soil with relatively good surface permeability;
  • Layout: narrow coal pillar gob-side entry typical of deep, high-efficiency mining.

3. Experiment design

3.1 Field monitoring

On-site measurements included:

  • Gas concentrations: CH₄, CO₂, O₂, CO;
  • Temperature dynamics in the return airway, narrow pillar, and adjacent goaf;
  • Pillar breaking degree, gas permeability, and goaf spontaneous combustion potential.

These support evaluation of explosion risk driven by spontaneous combustion.

3.2 Laboratory analysis

Lab tests on coal samples and gas collected on site complemented field data:

  • Coal hardness distribution in the pillar;
  • Gas composition/concentration patterns;
  • Temperature and free-radical type/concentration in pillar and goaf—linking macro gas exchange to coal–oxygen reaction theory.

4. Disaster-causing mechanism

The authors identify stress-driven fracturing of narrow coal pillars as the primary enabler of goaf spontaneous combustion risk. Two dominant failure modes:

| Mode | Gas path | Consequence | |------|----------|-------------| | Explosion pathway | CH₄ flows goaf → roadway | Roadway methane exceeds limits; ignition risk | | Combustion pathway | O₂ flows roadway → goaf | Residual coal oxidizes; temperature rises |

Macro analysis covers gas and combustion evolution on both sides of the pillar; microscopic analysis uses hardness, radicals, and reaction theory to set risk degree.

5. Risk area classification

5.1 Two core indicators

Using correlation coefficient criteria and safety principles, the paper selects:

  1. Gas-impermeability of the narrow coal pillar — how well the pillar blocks exchange;
  2. Risk degree of residual coal spontaneous combustion in the goaf — oxidation hazard in the goaf.

5.2 Three zones

Pillars and adjacent goafs are divided into:

| Zone | Management implication | |------|------------------------| | Dangerous Area | Highest composite risk; priority grouting / fire-extinguishing treatment | | General Area | Moderate risk; standard reinforcement | | Safe Area | Lower risk; lighter or deferred intervention |

Goal: maximize safety benefit per unit cost instead of blanket treatment.

6. Relation to later prevention work

Follow-on studies (e.g. inorganic fire-extinguishing materials for narrow pillars) cite the same mechanism: stress-induced pillar damage → higher permeability → coupled gas and combustion exchange. Zone-based classification provides a spatial template for material injection and sealing.

7. Limits and reproduction notes

  1. Site-specific thresholds: indicator cutoffs come from Yangquan No. 15 seam conditions—recalibrate elsewhere.
  2. Dynamic mining: pillar stress and fractures evolve with face advance; zones may need updating.
  3. Not a pure ML paper: value is in mechanism + zoning logic; pair with monitoring/forecast models (e.g. gas series prediction) for early warning.
  4. Prevention still physical: classification supports where to grout/seal; it does not replace ventilation, gas drainage, or interlocks.

8. Engineering takeaways

  • Treat narrow pillars as coupled gas barriers and combustion gates, not only support structures.
  • Prevention should be spatially differentiated—Dangerous → General → Safe.
  • Monitor CH₄, O₂, CO, temperature together; single-gas alarms miss coupling.
  • Combine zoning maps with grout/fire-extinguishing plans to avoid over- or under-treatment.
  • High model or lab scores do not replace methane monitoring, ventilation redundancy, and human confirmation.

Reference

Tang, Z.; Yang, S.; Xu, G.; Sharifzadeh, M. Disaster-causing Mechanism and Risk Area Classification Method for Composite Disasters of Gas Explosion and Coal Spontaneous Combustion in Deep Coal Mining with Narrow Coal Pillars. Process Safety and Environmental Protection 2019, 132, 182–188.