Does the welding machine current used in the manufacturing of acid resistant pump accessories in Dalian harm people?

Does the welding machine current used in the manufacturing of acid resistant pump accessories in Dalian harm people? Welding machine is a transformer, and the product of primary voltage and current is equal to the product of secondary voltage and current. In the manufacturing of acid resistant pump valve pipelines, welding machines are a type of step-down transformer. In order to melt the welding rod, a high current must be used. If the current increases, the voltage will decrease. The reason for low voltage is that it does not harm people. The human body resistance must be low and the voltage must be low. The current passing through the human body is very small and will not harm people.

But it cannot be said that welding machines will never harm people. If people stand in water, they will still harm others because the humidity will decrease and the human body will increase. Voltage below 12 volts will not harm people. The safe current that the human body can withstand is very small, only about 10ma. A current of over 10ma will cause noticeable sensations such as paralysis, stabbing pain, and difficulty breathing. If the current is greater than 50ma, there is a risk of electric shock. When the current exceeds 100ma, the human body may experience breathing difficulties, cardiac arrest, coma, and other symptoms.

Since the current that the human body can withstand is so fragile, why is the working current of the welding machine so high that it does not harm people? First, we need to clarify the relationship between voltage, current, and current circuits.

(1) In the manufacturing of acid resistant pump and valve pipelines, the current of the welding machine is indeed very high, usually over a few hundred amperes, but the current circuit only flows from the positive pole to the negative pole of the welding machine, without passing through the human body, as shown in the following figure (positive pole of the welding rod, negative pole of the welding piece). The current circuit of several hundred amperes is: welding tongs → welding rod → welding piece → grounding tongs, flowing back to the negative pole inside the welding machine from the grounding tongs, without passing through the human body! So no matter how high the current is, it will not cause harm to the human body!

(2) The average resistance of the human body is about 2000 Ω. If the human body touches the welding tongs (positive pole) with their hands and the welding piece (negative pole) with their feet, the current flowing through the human body is another circuit (rather than the circuit between the welding rod and the welding piece). According to Ohm's law I=U/R, the normal operating voltage of the welding machine is about 30V~45V. Calculated based on the average human resistance R=2000 Ω, the human current is about 15ma~22.5ma, which will not endanger life.

(3) According to industry regulations, the safe voltage for human body should not exceed 36V. The no-load voltage of welding machines can reach 70V, and the working voltage is 30V~45V. Therefore, welding machines are not without danger. If the human body current is greater than 50mA, it can be life-threatening. It can be inferred that if calculated based on a no-load 70V, R=U/I=70V/50mA=1400 Ω, which means that when the human resistance is less than 1400 Ω, there is a risk of electric shock. The human resistance is related to the body's constitution, the dryness of the skin surface, etc. When the human resistance is mainly concentrated on the skin surface, it will greatly decrease when the skin is moist. When the skin sweats, the human resistance will drop to about 1000 Ω. Therefore, there is still a risk of electric shock if electric welding is not careful. Therefore, the welding table shell must be grounded, and welding must be carried out in a dry environment. Wear safety insulated shoes, insulated gloves, etc.