Abstract: Based on investigating an accident of deflagration caused by electric welding construction, on- site inspection, investigation and inquiry, simulation test and infrared thermal imaging analysis were conducted and the causes of welding slag falling and smoking were excluded. After in-depth study of the mechanism of fire in the welding circuit, it was proposed that in the process of high-current arc welding, the weak contact parts in the welding circuit will form local overheating and high temperature, which can cause the fire on surrounding combustibles. The paper provides some new ideas for fire investigation of electric welding.

Key words: fire investigation, site investigation, simulation test, welding circuit; deflagration