Direct cause analysis
The kiln system Q235-A is made of steel and has good electrical conductivity. The main responsibility of the accident is that He has no special operation qualification certificate, which is an illegal welding operation.
1. He is ignorant of the most basic skills of electric welding operation. When welding, the left hand is holding the hook nail, the right hand is holding the welding handle, the welding hook is not in contact with the kiln body, and the load current passes through the lead wire, the welding rod, the welding rod, The hook nail, the human body, the kiln body, and the secondary side ground wire return to the electric welding machine to form a circuit for current circulation, so that the current passes through the human body, causing an electric shock death accident. If the hook of the weld is in direct contact with the kiln, since the resistance of the human body is much larger than the resistance of the metal, the current passing through the human body is small (can be ignored), and this personal electric shock accident will not occur.
2. He lacks electrical professional technical knowledge, does not wear special gloves during welding work; lead wire joints or insulated rupture conductors of electric welding are exposed; lead wires are exposed without shields.
3. When he was working on the electric welding machine, he did not strictly implement the relevant regulations of the “Electricity Production Safety Regulations” (thermal and mechanical parts). In violation of regulations, the current circulation circuit was caused, and the electric current passed through the body and caused electric shock.
When the current through the human body exceeds the current (16mA for men and 10.5mA for women), the human body cannot get rid of the charged body, and it will be extremely painful and unbearable. If the time is too long, you may stun, suffocate, or even die. The current of 30 mA is a dangerous current. When the current through the human body reaches or exceeds 30 mA, the heart beats irregularly, coma, blood pressure, and strong sputum. May cause ventricular fibrillation, causing death; 50mA current is called ventricular fibrillation current (or lethal current), that is, the minimum current that causes fibrillation in the ventricle through the human body, 50 mA current through the human body for 1 s, ventricular fibrillation may occur It kills people; when the current through the human body reaches 10 mA, people may die in a short period of time.
The resistance of the human body is generally between 1 and 2kΩ. If 7V is applied to the human body, according to Ohm's law, the current through the human body will be 35~70mA. This current is 2~4 times of the current of the adult man. Adult women get rid of the current 3 to 6 times, for people with low resistance, they have reached or even exceeded the lethal current (50mA), and the human body's resistance will drop in the humid environment, so the current through the human body will be bigger and fatal. .
When conducting the operation of the electric welder, the electric welder must strictly implement the relevant provisions of the "Electricity Production Safety Regulations", and wear safety gloves, shoes and socks and other insulation protection products. Other personnel without special operation qualification certificates, or do not understand People with electrical knowledge should not operate the welding machine without authorization to avoid personal accidents.