1️⃣ Introduction

Coal dust is a highly explosive hazard in underground coal mines. When suspended in air and ignited by a spark or explosion, it can propagate a mine-wide blast. To prevent such disasters, DGMS mandates the treatment of coal dust with incombustible dust (stone dust) under Regulation 123 of the Coal Mines Regulations, 2017. This practice dilutes the explosibility of coal dust by increasing the incombustible content, thereby preventing flame propagation.

2️⃣ Objective of Stone Dusting

• To render coal dust inert and non-explosive.
• To prevent secondary explosions after firedamp ignition.
• To maintain safe working conditions in longwall, gate roads, and returns.
• To comply with DGMS statutory requirements.

3️⃣ DGMS Legal Framework

4️⃣ What is Incombustible Dust?

Incombustible dust is any non-flammable fine material (usually limestone dust or stone dust) that, when mixed with coal dust, reduces its combustibility.

5️⃣ Methods of Application

1. Manual Stone Dusting: Carried using blowers or hand sprayers. Applied on roof, sides, and floor.
2. Mechanical Stone Dusting: Done using pneumatic machines or tankers in mechanized mines.
3. Barrier Stone Dusting: Stone dust barriers installed along roadways to stop explosion propagation.

6️⃣ Standards for Incombustible Content

7️⃣ Sampling & Analysis Procedure

(a) Sampling: Carried out by Dust Sampling Officer/Overman once every 14 days. Dust collected from roof, floor, and sides into sealed containers.

(b) Laboratory Analysis: Samples analyzed for incombustible matter percentage. Standard DGMS-approved method involves heating and weighing residue after burning coal content.

(c) Record Keeping: All results recorded in Form IV of the Coal Dust Register. Reports sent monthly to DGMS Regional Office.

8️⃣ Importance of Sampling

• Ensures continuous compliance.
• Detects ineffective or missing stone dusting.
• Prevents chain explosions.
• Helps in audit and investigation by DGMS.

9️⃣ Common Reasons for Non-compliance

• Inadequate or uneven dust application.
• High humidity causing stone dust to cake.
• Poor sampling frequency.
• Leakage of air carrying coal dust into returns.

🔟 Precautionary Measures

• Use dry, fine (<200 mesh) stone dust.
• Avoid contamination with coal dust.
• Maintain dust barriers after blasting.
• Replace caked or damp dust periodically.
• Record each stone dusting operation in the logbook.

⚡ Quick One-Liners (Revision Points)

• Coal dust is explosive in nature.
• Stone dust makes coal dust inert.
• Incombustible content ≥65% (intakes).
• Sampling every 14 days mandatory.
• DGMS Circular 08/2015 gives test methods.
• Barrier stone dusting prevents explosion spread.
• Limestone (CaCO₃) is most used inert dust.
• Record results in Form IV.
• Humidity reduces dust effectiveness.
• DGMS enforces 90% inert content near face.

🧠 Descriptive Model Question & Answer

🎯 25 MCQs – Coal Dust Treatment & Sampling