This video from Würth Elektronik elaborates on clearance and creepage distance and solid insulation materials.
Many applications of fire are productive and warming. Fire can be a real risk if the components on pcb has not been selected correctly for high voltages.
In some circumstances, incorrectly selected components can create Transient voltage, which could cause damage to the board and even leads to spark fire. To achieve electric shock protection, electronic equipment must have an effective insulation method, which can be divided in to clearance and creepage distance and solid insulation materials.