Crawling and electrical outlets

My daughter has just started moving. We are fortunate that she started moving later than some other babies we know.  We have had a blissful 10 months of not having to chase after her and put up gates in the house. Alas, that is all over now.

She is not crawling exactly, but she scoots forward. She reaches forward onto her hands while sitting and uses one leg to pull herself forward and drags the other leg behind. I have seen many of her cousins doing something similar, at pretty high speeds. This may turn into a standard crawl someday soon, or maybe not. Either way, she is definitely moving around, and faster every day.

Last week, I put her down on the floor in the bedroom so I could pick up some clothes to do some laundry. She usually goes straight to playing with our window shades, which is relatively safe. That day, though, I turned my back for just a second and she went straight across the room to the electrical outlet. Yikes! I had not yet put the safety plugs in upstairs. It is crazy how she always goes straight for the electrical outlets. They are right at eye level and are apparently quite fascinating.

So why are electrical outlets so dangerous for little ones?

First of all, can she even get her little fingers in those tiny little holes? In order for an electrical connection to be made, she needs to touch the metal connections. Even with her very little fingers, I do not think she could get them into the outlets. That being said, I certainly do not want to let her try!

I think the real danger is probably having her put one of her toys into the outlet and making an electrical connection that way. Many of her toys are plastic or rubber right now, which do not conduct electricity effectively, but she does love to play with metal things. Also, she gets into everything now that she is mobile and I let her play with anything that does not seem dangerous, so it is not unlikely that she would find something to put into that outlet.

What happens if she does manage to get something into the electrical outlet (finger, fork, etc.)? The outlet has 120 V of potential – that means that it has energy that is ready to start flowing. If you ‘complete the electrical circuit’, i.e. give that energy somewhere to flow, it will start flowing – through you.

So how much current will flow through your body if you touch an electrical outlet and what is a dangerous level? Ohm’s Law tells us that voltage, V, (that 120 V for a standard household outlet) is related to current, I, and resistance, R, through the following equation:

The amount of current that flows through us depends on our resistance to that current.

So what is our resistance? That turns out to be a complicated question because it depends on things like how dry (or wet) our hands are, and how much contact we make with the metal wires. If we connect with the wires over a large area of our bodies, our resistance is lower – it is easier for current to flow through us.

Dry skin has a larger resistance than wet skin. This is fortunate for me as a teacher. I accidently shocked myself with a 500 V source in the lab once, but my hands were covered in chalk and the contact between my hands and the wire was small. It was definitely not a pleasant shock, and I felt dizzy for a little while after, but there was no serious or permanent damage. On the other hand, I have also shocked myself on a 120 V outlet in a lab (no chalk) and it was quite painful. Who knew the life of a physicist could be so dangerous?

But I have not answered the question. What is our resistance? I had my students measure their resistance in a teaching lab using very small metal probes (small area of contact). They measured from one hand to the other and found that they had a resistance of about a megaohm – that’s one million ohms. However, an article on Electric Shock on Wikipedia cites the International Electrotechnical Commission as showing adult resistances at 100 V of ~2000 ohms. They use larger contact areas, but you never know when you shock yourself how much contact you will have, so it is much safer to assume your resistance will be low.

Okay, let us assume, to be safe, that our resistance is about 2000 ohms and the voltage of the outlet is 120 V. From the equation above (Ohm’s Law), we can calculate that this situation would send 60 milliamps (mA) of current through us. That does not sound like a lot, right? Well, an amp is a LOT of current. The same Wikipedia article cited above states that humans can feel 1 mA of current. Currents as low as 60 mA (and sometimes lower) can cause fibrillation of the heart muscles, which can lead your heart to stop.

Depending on the voltages and contact situation, electrical shocks can also cause serious burns. I had minor burns on both hands when I was shocked by the 500 V lab source. (I should note that I am always very careful around electrical sources and in both cases of being shocked, I was working with wires that had been previously damaged  – a good example of why you should always have broken or old wiring repaired immediately.)

Okay, I am convinced. I should cover up my outlets and keep my daughter safe! So far we have just put in some standard outlet covers, though I have read in several places online that these covers are too easy for toddlers to remove. Fortunately, my daughter is too young to have figured that out yet (and trust me, she has tried!). As she gets older, and stronger, and more coordinated, and smarter, we may have to come up with better ways to keep her safe.

We are definitely entering a new stage of parenting. It is amazing to watch her learn to move and explore her world and I am very much enjoying it, but with every new development comes new challenges.