Safety

How safe is it to sleep with an electric blanket?

I have slept with an electric blanket for the last 20 years with no ill effects.  But of course we check it occasionally and get a new one if there is significant damage.  They generally last only 8 to 10 years.  The electrocution hazard is virtually zero given that you look after it as on the instructions.

There are a few dos and don’ts though.

The big problems are due to overheating.  Make sure that they are not switched on with a load of material on the bed other than the normal bedding which can cause them to overheat.  They shouldn’t be switched on when folded etc.  And you shouldn’t sleep with the level turned up above a point which will maintain a just comfortable level.  If you go to sleep with it on high you can become overheated.  Most people will wake up if that happens because it is too uncomfortable.

It is best not to use them for very old people or young children.  They often don’t understand or don’t remember that they shouldn’t sleep with them on high.  Especially important since they have poorer body temperature control.

Some electric blanket need to be inspected by the manufacturer (or an agent) every few years.

Note that there are two types:

  • Those designed to pre-heat the bed before you get in.
  • Those you can sleep on with the power on.

Check which type you have. Personally I’m too hot in bed to need one so my wife says 😉

The worst thing you could probably do would be to use one folded so that the insulation was strained. After some time (probably still many years) the insulation at the fold might fail. Then if you were to say “wet the bed” (by spilling your warm milk – what did you think I meant?)  that would reduce your bodies contact resistance and you might get a shock. Follow the instructions and they are very safe. Take it off the bed in summer to extend the blankets life.

Here is a question asked by one of our readers:

I recently received one as a gift and have not yet tried it. My concern deals not with EMF, but with the hazard of electrocution. I looked at the back of the control box and saw that the power rating of the blanket is 180 Watts. Now, at 120 Volts, that means the blanket is carrying 1.5 Amps of AC electricity through the wires whenever it is on, which (I believe anyway) is more than enough to kill a healthy person.

The severity of an electrical shock depends on both the electrical voltage and current you are subjected to. Technically, the severity of electrocution depends on the amount of power dissipated by the body, wether it be 60hz AC or DC. If voltage is the only thing that mattered, then millions of people per year would be killed instantly when they dragged their feet across the carpet in winter and touched the doorknob – that little spark is probably 8 thousand volts or more… so no, 120v is NOT going to instantly kill you, sheesh give the guy a heart attack…

The probability of getting killed by an electric shock is determined by the current through your body.  Not wattage nor voltage.  The level which is considered lethal is in the range of about 100 mA to several hundred mA for normal healthy people with surface skin exposure.  (Above this level and there is a fair chance the person will survive – the heart etc seems to be completely stopped but then often restarts spontaneously if the shock is of short duration).

The current through the person is determined by the voltage across the body and the resistance due to body tissue, whether the contact area is wet or sweaty etc.  For most people, most of the time simply touching 120 V for a short time is not lethal.  Unless for example the blanket wire was broken and you grabbed both exposed ends of the wire with wet or sweaty hands.  Or you touched the exposed wire and was standing on a wet floor in bare feet.

The mains voltage of 120 V in the US is certainly not lethal in most situations.  Unlike here in Australia and a lot of the rest of the world where the standard voltage is 240 V.  Touching an exposed wire here is much more dangerous.

The reason higher voltage causes more severe shock is because of the body’s naturally high resistance (or low conductance, if you prefer.) If a person holding a live wire is equivalent to a 10k resistance (which is very conductive like holding onto two electrified bars), then at 10v, ohm’s law states that V=I*R or I=V/R, so current I = 10/10,000 or 0.001 or 1mA. Power is the voltage * current, so the power dissipated at 10v through this 10k resistance is 0.01 watts. This is an insignificant amount of power and would barely be felt by the individual, if at all. But if the voltage in question is a high-tension residential distribution voltage, which in my neighborhood is 18,000v, then the picture is much more bleak: I = 18,000/10,000 = 1.8 Amperes current, and the power dissipated into that 10k load is 32,400 watts. We all know what a 1000w microwave oven does, well that shock would be 32.4 times as “hot.”

120v mains at 10k resistance is 12mA or 1.44w. This would definitely be painful, but *not* necessarily lethal.

Now it IS possible to be electrocuted by 120v mains, that’s for sure. And in rare cases, it is possible to be injured severely by mains voltage. But unless you lick your palms and grab onto the hot lead with your left hand, and the neutral with your right.



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