Thermo-Chemical Evaluation of Foam-Based Filling Materials for Fire Prevention in Underground Coal Mines

This study evaluates phenol-based chemical foams – phenol-formaldehyde (PF) and phenol-urea-formaldehyde (PUF) – for fire prevention, sealing, and reducing spontaneous combustion risk in underground coal mining. Four formulations (PF-A, PF-B, PUF-C, and PUF-D) were tested for mechanical properties, thermal behavior, and formaldehyde emissions. PF-A showed the highest thermal stability with a CPT of 231°C, outperforming other foams due to its unique pore structure. It also had a low apparent density of 22.8 kg/m3 and a compressive strength of 34.4 kPa, making it lightweight and mechanically stable. In contrast, PF-B, PUF-C, and PUF-D had lower CPTs and more porous structures, reducing thermal stability. PF-B had higher density but lower strength, while PUF-C and PUF-D exhibited weaker compressive properties (13.3 and 17.9 kPa) and lower densities, limiting structural suitability. Regarding safety, PF-A emitted formaldehyde at 0.36–0.40 ppm, below OSHA limits, whereas PF-B reached 3.5–5.6 ppm, necessitating strict PPE along with PUF foams. Overall, PF-A offers the most balanced combination of thermal stability, mechanical performance, and manageable emissions. While PUF foams are safer in emissions, their reduced strength and stability highlight the need for optimized formulations to ensure both structural reliability and worker safety in underground mining.