# Mining Contract: Strengthening an Existing 20-PSI Mine Seal with PPG's Polyurea Coated Retrofit

Keywords:Data analysisModelingPlastics and polymersPressureSeals

| Contract #                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | 200-2007-20426 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|
| 5/27/2007                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| 8/29/2008                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| PPG Industries was awarded a NIOSH contract to develop a spray applied polyurea coating system that would upgrade existing 20-psi approved mine seals to withstand blast pressures greater than 60 psi. The research program coupled modeling predictions from Penn State's Applied Research Laboratory (ARL) and synthesis and formulation expertise from PPG. The research program had three main elements:
- Modeling  - Use finite element modeling to predict and recommend a seal and coating design capable of withstanding a static horizontal blast pressure of 60 psi.
- Formulation  - Develop a flame-retardant, spray applied polyurea coating that can be applied at 50-60°F with enhanced blast performance properties.
- Validation  - Test the polyurea coated retrofit mine seal at NIOSH's Lake Lynn Experimental Mine with full-scale blast tests.  |
| - Seal Design                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |

## Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

The program goal was to increase the mine seal blast pressure sustainability of a baseline 20-psi seal to greater than 60 psi. Analysis and testing were completed for using a polyurea coating to improve blast effectiveness of a mine seal:
        - The MICON 550 seal was selected for analysis and testing for the polyurea coated specification. The baseline seal used two walls of dry stacked solid concrete blocks separated by a 16"-thick polyurethane core. This unmodified seal was an approved 20-psi mine seal. A coated retrofit design was developed for the MICON 550 seal which includes a secondary 8"-thick polyurethane core, secondary block wall, 0.125"-thick polyurea coating, and a flame-retardant latex coating. The retrofit configuration was installed and tested at the Lake Lynn Experimental Mine, and survived two separate blast tests with peak blast pressures of 78.5 and 84.4 psi.
        - An alternative seal design was also analyzed with and without polyurea coating. A solid concrete block seal was selected for analysis. The uncoated seal was rated at 50 psi, and was predicted by models to fail at 70-psi peak blast pressure. The coated seal was predicted to survive a minimum 90-psi blast using conservative predictions of potential coating failure.

The completed analyses and testing showed that the PPG polyurea coating can improve the blast protection of mine seal structures.

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          - Computational Research
          - Design and Analysis of a New Method to Test Mine Seals
          - Evaluation of Explosion-Resistant Seals, Stoppings, and Overcast for Ventilation Control in Underground Coal Mining
          - Explosion Pressure Design Criteria for New Seals in U.S. Coal Mines
          - Methane Diffusion Parameters for Sized Coal Particles: A Measuring Apparatus and Some Preliminary Results
          - Modeling and Data Analysis of 50 to 5000 kHz Radio Wave Propagation in Coal Mines
          - The NIOSH Shield Hydraulics Inspection and Evaluation of Leg Data (Shield) Computer Program
          - Strengthening Existing 20-psi Mine Ventilation Seals With Carbon Fiber-Reinforced Polymer Reinforcement
          - Structural Analysis and Design of Seals for Coal Mine Safety
          - Task Analysis

July 18, 2016

July 22, 2014

National Institute for Occupational Safety and HealthMining Program

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