How Confident Are You in Your Electrical Safety Knowledge? Take This Quiz to Find Out

Dear Friends,

A simple quiz on electrical safety is attached. Please try to answer and see where you stand.

Regards,
Kesava Pillai

Dear Dipil,

I understand that there were some doubts regarding which is more dangerous to the human body - AC or DC.

For ignorance, we have no cure. Instead, if the engineers had asked for some light, we could have provided it.

Electrical engineers are good in their field - making electricity work for them. The majority we have come across had never even considered the effects of electricity on the human body. They know that electricity can cause shock and death, but their responses to other safety matters are often imaginary!

Now, just ask them: What is ventricular fibrillation? What amount of current is required to cause ventricular fibrillation? What is the minimum voltage at which one can feel electricity? What is the average resistance of the human body? What is the maximum resistance of the human body? Which part of the body has the least resistance? What is the minimum voltage required to pass sufficient current through the body to kill a person? There are many more aspects for a safety/electrical engineer to understand in this field.

Regarding our issue: Ask them what the difference is in the RMS value of AC and DC.

Kindly send these answers if you could obtain them from the engineers who claim that DC is more dangerous than AC. Upon receipt, I may be able to advise ASKCRITERION to provide the exact reasons why AC is more dangerous than DC.

Regards,

Kesava Pillai.

Dear sir,

Let me try to answer the above questions:

1. What is ventricular fibrillation? What amount of current is required to cause ventricular fibrillation?
Ventricular fibrillation is a serious heart condition that may lead to death. It occurs at 50 to 100mA.

2. What is the minimum voltage at which one can feel electricity?
1 to 8 mA is perceptible but not painful.

3. What is the average resistance of the human body?
- Dry skin: 100,000 to 600,000 ohms
- Wet skin: 1000 ohms

4. What is the maximum resistance of the human body?
I am not sure about it.

5. Which part of the body has the least resistance?
Ear to ear has around 100 ohms.

Regards,
Hansa

Dear Hansa,

This is just an attempt, but it is not clear for people to understand. In your response, you mentioned the current, whereas the question pertains to voltage. Regarding points 3 and 5, yes, your answers are nearly correct. You have actually addressed this in point 3. Let us wait and see for a few more days to resolve the issue, please.

Regards,
Kesava Pillai

Dear Sir,

Please go through the attached file. Four answers from people in different fields are attached. I am requesting you to provide the exact answers to the mentioned questions.

Also, please help in answering the following two additional questions:

1. Why are we advising the usage of a 24V supply? Why should we believe a 24V supply is safe?
2. How can earthing reduce the risk of receiving an electrical shock?

With regards,
Dipil Kumar V

Dear Friends,

I always insist, "While a safety man advises others on safety issues, he is not to assume things and say 'I think...'." He has to give a definite answer - either yes or no. Often, a safety issue becomes a matter of life and death, as in the case of a confined space entry or a heavy lift. We cannot take chances. We have to be certain in such issues. With regard to electricity, we have to be quite serious. If one is not sure, he need not be ashamed to ask for experts/consultants.

As I mentioned, electrical engineers are often not trained in safety. For sure, they should be trained in safety and CPR. From the replies provided by them, you can see where they stand and why they consider DC is more dangerous than AC. It is their opinion only. They are not sure.

The comparison on the effect of DC and AC is attached (current in milliamperes):

1. AC is more dangerous than DC.
2. If our AC power supply is 220 Volts (RMS), then the actual peak voltage is about 310 V. (To get the same effect of, say, DC 220 volts, we require a peak voltage of 310 in AC, and we call it AC 220 V.)
3. Interference with the normal rhythm of the heart causes the condition called ventricular fibrillation. In this condition, fibers of the heart muscles, instead of contracting in a coordinating manner (which causes the heart to act as a pump), contract separately and at different times. When this happens, the heart's lower (pumping) chambers contract in a rapid, unsynchronized way. (The ventricles "flutter" rather than beat.) The heart pumps little or no blood. Blood circulation ceases, and (unless proper resuscitation efforts are made) death ensues. The heart cannot spontaneously recover from the condition. It is estimated that 50 mA is sufficient to cause ventricular fibrillation.
4. 1.5 volts, a pen torch cell if touched with your tongue, you feel the effect of the current.
5. The average resistance of the human body is considered as 1000 ohms. Internal resistance is 400-600 ohms.
6. 600,000 ohms. The skin on the palm of a village blacksmith who never used gloves in his life, who can take a heated iron piece with his bare hands, and sole of an old man who never used footwear in his life. Callus - the dead cells or thickened skin on their hands and sole has that resistance.
7. Between the ears, we have the least resistance of around 100 ohms only.
8. The minimum voltage required to pass sufficient current to kill a person is around 60 volts.

If the frequency is increased to thousands, probably we may not even feel electricity. The normal supply frequency of 50 or 60 Hz (as in the USA) is all the more dangerous.

Regards,

Kesava Pillai

Dear Sir,

Great reply! Thank you very much for sharing! I will share the information with all who participated in the discussions, with your kind permission. Could you please elaborate on the last sentence? Why is it so?

"If the frequency is increased to thousands, we may not even feel electricity. The normal supply frequency of 50 or 60 (as in the USA) is all the more dangerous."

With regards,
Dipil Kumar V