# Static electricity and door handles

I have a pair of shoes, which seem to isolate me from the ground. In effect I'm gathering static charge and every time i grab an aluminum door handle, that current discharges and that hurts. Ouch.

I invented a way to workaround that: when I'm going to touch door handle, first I take my Skeletool (a stainless steel multitool) and touch the door handle with it. Sometimes I even see the small spark and hear the discharge and then I can touch the handle myself unharmed.

But what interests me is: why discharging through the multitool does not hurt? This is an electrical current flow what hurts and the current flows the same way even if I hold the tool in my hand. Tool has surely less resistance than human body, so it shouldn't change anything. But it does not hurt :)

Why?

• Instead of using the tool, just touch the doorhandle with the back of your hand before gripping it. It's much less sensitive and less pointy, too, so not at all painful. Apr 13, 2015 at 12:32
• Or (if it's not a metal door) touch the door itself first (I usually use my foot). Stay in contact with the door, then touch the handle. Apr 13, 2015 at 20:02
• There are thousands of tricks - keys, elbows, anything that avoids an arc from your fingers to the door handle. Apr 14, 2015 at 14:30

When discharging without a tool, the whole charge exits your body through a small skin surface area, say $$0.1$$ mm$$^2$$.

When you hold a tool that surface is much bigger; perhaps $$100$$ cm$$^2=10,000$$ mm$$^2$$.

That means that the current flowing through neurons in that area is much lower, and perhaps low enough as to not be felt.

Pretty much the equivalent of spreading the same electric current through $$100,000$$ cables instead of $$1$$.

• Not to mention the heat generated by the arc and the reduced cross-section of the exit point. It's the spark that hurts, not the minute current
– Jim
Apr 14, 2015 at 13:26

As you walk across the floor, the soles of your shoes attract electrons from the carpet, and those electrons build up all over your body.

Here is a mechanical explanation of the pain you feel when electricity escapes your body via a small area on your fingertip:

The excess charges want to find a way off your body, and if a doorknob becomes the path of least resistance, the air between your hand and the doorknob expands and becomes a plasma as the air molecules are ionized by charges escaping from your finger. After the excess electricity flows out, air rushes into the expanded space with an audible "pop". Your nerve endings are stimulated by the heat of the plasma and mechanical action of imploding air.

When the path is through a multitool, the tool and the doorknob absorb the effects of the air expanding, heating, and imploding. Your skin does not participate in changes of the air through which the spark travels. That is one reason there is no pain. You effectively have placed yourself upstream of the effects caused by equalization of the electric charges in your body and the doorknob.

• I just put a water droplet on my finger, placed the tip of a piezo electric lighter inside the droplet, and the shock did not seem to have a difference. I doubt mechanical effects caused by air expansion are felt at all (there was no air to form an arc).
– user
Apr 13, 2015 at 13:30
• Additionally i suspect that thermal conductivity plays no role either. The shock duration is very short and skin thermal conductivity is quite low.
– user
Apr 13, 2015 at 13:35
• Good points. If your biological analysis is correct, I must yield to your experimental results! Particularly if the water droplet doesn't deform during the electrical transmission process in a way that could cause pain other than from concentration of the charge at the fingertip. Apr 13, 2015 at 23:27
• There were no visible changes in the droplet. Of course human vision is not a very accurate measuring instrument, but i wouldn't expect changes to be honest.
– user
Apr 14, 2015 at 6:35