The situation

West Bokaro was originally extracted using bord and pillar techniques. When the mine was converted to a surface operation, coal in developed but unmined underground galleries eventually caught fire. The fire was first observed in the Q-AB mine in 2021 and spread to Q-SEB. The fire continues to burn, predominantly in seams X and VII. At the time of writing, 40% of coal mined comes from fire affected zones.

The active fire heats the overburden which causes the temperature of some blastholes to exceed 55°C. Conventional non-electric initiation systems and packaged emulsion explosives are not suitable for inhole temperatures above 55°C. The integrity of these products degrades at such temperatures, with a high potential to cause misfire between 55°C and 100°C. At higher temperatures unplanned initiation is possible.

In 2022, Orica completed reactivity testing for 13 rock samples collected from Q-AB, and a few samples were found to be reactive with nitrates at temperatures above 55°C. Thus, West Bokaro has a hot and reactive ground situation.

Technical solutions

Special inhibited explosive and initiating systems

Senatel™ Pyromex™ is a water-resistant packaged emulsion specifically formulated to inhibit exothermic nitrate reactions in reactive ground. Its combination of high detonation velocity and energy, coupled with its robust nature makes it a reliable primer for ANFO/emulsion blends such as Fortis™ Vulcan™ or Simex™. Senatel™ Pyromex™ can also be used as a column explosive. The permitted sleep time depends on the temperature and may be limited by the initiation system.

Over a period of three months, TSL and Orica conducted field trials of Senatel™ Pyromex™ for the first time in India. This inhibited explosive can be safely used in holes up to 100°C¹.

1 - When enclosed with a special shell and initiated with RDX detonating cord, Senatel™ Pyromex™ can be used in holes up to 150°C.

Cordtex™ Pyrocord, a PETN based detonating cord designed for use in holes up to 100°C, was used as a downline. The cord downlines were initiated at the blasthole collar with i-kon™ III RX electronic detonators. Although these products are rated to 100°C by Orica, during the trial they were only used in holes up to 80°C to comply with G.S.R. 986(E) of Gazette Notification issued by the Directorate General of Mines Safety (DGMS).
 

As part of the project, an Orica expert on hot and reactive ground blasting visited the site to help develop standard operating procedures (SOPs) and train the blast crew on safe loading and blast sleeping techniques in hot and reactive ground.

Precise temperature measurements

A key procedural control for safe blasting in hot and reactive ground is blasthole temperature logging. At West Bokaro, in-hole temperatures are measured twice, at least 4 hours apart, using a K-Type thermocouple.

The two measurements are used to decide if each blasthole is safe to load. If either measurement exceeds 80°C, or if the two measurements differ by more than 5°C, the blasthole is not loaded.

The result

During the trial activities, 9,650 kg of Senatel™ Pyromex™ were used for blasting in hot and reactive ground.

• 3 blasts consumed 999 kg of explosive in normal ground conditions to train personnel on charging practices with the hot and reactive ground products.
• 21 blasts consumed 7,837 kg of explosive in hot ground above coal seam X in Q-AB and Q-SEB.
• Multiple blasts consumed 814 kg of explosive using Senatel™ Pyromex™ cartridges as primers for bulk explosive in normal ground, to prove compatibility and reliability as a booster for inhibited bulk explosive. 

The trial blasts used 165 mm diameter blastholes on bench heights ranging from 3 to 11 metres. The average powder factor achieved was 3.5 bcm/kg (0.29 kg/bcm). The maximum temperature measured was 79°C.

We recently conducted a field trial of Orica’s inhibited explosive, Senatel Pyromex at our West Bokaro Division, where hot and reactive ground conditions are a consistent operational challenge. The product was deployed in blast holes with temperatures reaching up to 80°C, strictly adhering to site-specific SOPs and regulatory guidelines.

Senatel™ Pyromex demonstrated excellent thermal stability throughout the trial, with no instances of misfire, cut-off, or unplanned initiation. The performance was not only safe and reliable but also yielded impressive fragmentation results, contributing to improved downstream efficiency.

We are highly satisfied with the outcome of this trial and appreciate Orica’s support in introducing a solution tailored for such demanding ground conditions.

— Mr. Narendra Kumar Gupta Chief (Agent): Q-SEB West Bokaro, Tata Steel Ltd.

Acknowledgements

Orica are grateful for the collaboration with the West Bokaro Site Team and Tata Steel Limited, giving us the opportunity to jointly implement introduction of a first-in-India inhibited explosive for blasting in hot and reactive ground. This initiative sets a precedent for the Indian mining industry for making operations with such challenging environments safer and efficient.