Coal Inspectorate | Alert | No.387 V 1 | 19 February 2021

Use and application of Polyurethane Resin (PUR) in underground coal mines

Key issues

Background

Operators of underground coal mines should be aware of the capability of polyurethane resins (PUR), to cause heating of coal due to exothermic reaction. It is essential that effective risk control measures are implemented when PUR is used in underground mining operations for the purpose of strata consolidation.

A recent investigation has considered the application of PUR for strata consolidation as a potential cause of heating of remnant coal. Investigations have identified that the use of PUR for strata consolidation has the potential to cause an exothermic reaction that is capable of heating surrounding coal sufficiently to create an ignition source.

The following recommendations are provided to Site Senior Executives (SSEs) of mines to assist them in ensuring risk control measures are effective for the use and application of PUR in underground coal mines.

Recommendations

Risk assessments

Whenever a risk assessment is conducted or reviewed for the application of PUR, the following should be considered:

• All relevant technical documents and approvals for PUR should be reviewed and referenced by the risk assessment team including the:
  • current NSW licence for the PUR and its requirements
  • NSW test results for exothermic reaction
  • German (Arnsberg) approval and test results
  • supplier's technical data and information.
• All requirements for the use of PUR specified in any licence or approval must be addressed in the risk assessment and have effective controls recorded and approved by the Underground Mine Manager (UMM). The UMM and SSE must ensure that the controls are effectively implemented.
• Participants in the risk assessment should include a cross section of coal mine workers with appropriate technical expertise, including PUR technical specialists, Geotechnical Engineers, PUR specialist applicators, UMMs and other relevant statutory personnel.
• The potential for PUR to artificially raise the temperature of coal can be exacerbated by circumstances, including not limited to:
  • PUR concentrating or disproportionately accumulating in and around coal and other rock types with a propensity to self-heat
  • specific geological conditions that can influence PUR migration behaviour e.g. magnitude of fracturing and proximity of cavities
  • PUR hole spacing and design i.e. the justification of hole and PUR volume concentration must be considered with respect to each application of PUR.
• SSEs should ensure that their mine's safety and health management system (SHMS) contains adequate requirements for risk assessment processes to ensure that coal with an artificially-raised temperature (as a result of the use of PUR) does not enter the goaf. The SSE should ensure that these risk assessment processes are effectively implemented at the mine to ensure the risk is as low as reasonably achievable. In particular, risk assessments should be conducted for each application of PUR to ensure specific risks and hazards relevant to individual mines are appropriately assessed and managed.

Ground consolidation plans

• All PUR application/consolidation plans should be designed and authorised by an experienced Registered Professional Engineer Queensland (RPEQ), or equivalent, Geotechnical Engineer and approved by the UMM for each application.
• The development of strata consolidation plans that require the use of PUR should specify the installation requirements including hole design (spacing, angle and length), product quantity, and verification processes for compliance against the plan, to be approved by the UMM for each separate polymeric application. Strata consolidation plans should also consider, in an appropriate matrix, the risk of the combination of coal and PUR entering and remaining in the goaf.
• The SSE should ensure that the SHMS for the mine includes an effective system to monitor, control and record volumes of PUR used for each application. The SSE must ensure that the system is effectively implemented to ensure that the risks associated with using product in excess of the prescribed volume is reduced to a level that is as low as reasonably achievable for each application of PUR.
• UMMs should require and approve fire watch inspections and appropriate recording systems for each PUR application. Fire watch inspections should include:
  • the use of surface temperature monitoring
  • temperature monitoring of injection holes
  • gas monitoring pre and post the affected coal entering the goaf
  • ventilation readings
  • indications of spontaneous combustion¹.
• The specification for fire watch inspections should be included in the mine's SHMS.
• UMMs should ensure the development of a Trigger Action Response Plan (TARP) for PUR inspection requirements. The TARP should:
• include set temperature ranges and gas concentration levels
• specify the time period in which production can recommence. The time for recommencement of production should consider the proximity of the PUR to the mining environment and goaf.

¹ This is not an exhaustive list and each mine should ensure appropriate risk assessments are conducted to ensure that Fire Watch inspections can manage risk to a level that is as low as reasonably achievable.