Phosphorus is burning, and human bones contain more calcium phosphide. People are dead, bodies are buried in the ground to rot, and various chemical reactions are taking place. Phosphorus is converted from phosphate to phosphine. Phosphine is a gaseous substance with low ignition point, which will burn when it comes into contact with air at room temperature (Ca3p2+6H2O = = 2ph3+3ca (OH) 2, PH3+2o2 = = h3po4). After phosphine is produced, it is emitted into the air along cracks or holes in the ground, and emits blue light after burning. This is phosphorus fire, also known as "ghost fire". Even if biogas/methane is generated, the ignition temperature of methane is 538℃, which can't be spontaneous combustion.