Take insulation measures in wet environments

1. Accident process:
During the overhaul of a hydraulic press in a workshop, it was found that there was a crack in a section of the pipeline leading to the operating valve in the trench. After discussion between mechanic B and welder A, arc welding was used for welding. Welder A entered the trench from the trench entrance. A straw mat was laid in the trench. A lay on the straw mat and welded with welding rods. During the operation, the welding clamp had short-circuited on the iron frame of the trench, generating sparks, but A did not pay attention to it. Welder A came out to get the welding rod and entered the trench for the second time. A's legs were kneeling in the trench, his buttocks were close to the iron frame of the trench entrance, his left hand was supporting the ground in front, and his right hand was holding the welding clamp behind his right shoulder. When he lowered his head and was drilling forward, the end of the welding rod held by the charged welding clamp accidentally touched the back of A's right neck. A screamed immediately and lost consciousness. At this time, Yi, who was standing at the entrance of the trench, immediately ran to the welding machine 8m away and turned off the knife switch. After dragging A out of the trench, he died after artificial respiration and other rescue efforts.

2. Cause Analysis
(1) The no-load voltage of the welding machine used by welder A was relatively high, 100V, which was much higher than the safe voltage.
(2) Because it was summer and he was working in a narrow space, his body was sweating during the first welding repair, and his body resistance would be reduced. When A entered the trench for the second time, his buttocks were close to the iron frame, which had been accidentally electrified. When the welding rod touched his neck, the current just passed through A's body, causing electric shock. Due to the humid environment, sweating, and high voltage (up to 100V), the body resistance may drop to 7700Ω at this time, and the current passing through the body may reach 130mA, causing heart paralysis and death.

3. Lessons learned
When welding in a damp and narrow environment, reliable insulation measures must be taken. Two welders should take turns to work and monitor each other, otherwise it is not suitable to work: If abnormal conditions are found during the operation, the cause should be found in time. Eliminate hidden dangers, such as sparks generated by contact between the welding clamp and the iron frame, which can be eliminated in time, and this accident can also be avoided. The electric welding machine should be supervised by a dedicated person, and the welder should be contacted in time. The knife switch should be closed during welding, and the power supply should be cut off in time after welding.