Induction

[Lopsided]

I have recently got a new induction electric cooking hob in my kitchen. I live in a flat so cannot use gas. It is incredible, you put a pan on it, stainless steel or cast iron, and the contents of the pan gets hot really quickly, but the surface of the hob remains cool. It does it by inducing heat into the nearby metal of the pan.

If I stand too close, can heat be induced into the metal of my resurfacing? Am I silently cooking the innards of my hip? The hob is at hip level too! My hip, and the device in it, are only inches away from the hob.

Generally I leave cooking to the missus. But in any case, is a modern cooking appliances an unrecognized danger to high tech alloy implants? Anyone got any ideas?

D.

[Luann]

Hey Dan,

For those of us: out west, yankees, in the "states" (you know, those of us speaking REAL English :)!!  You may want to tell us what a hob is. (I know, if I spoke real English, I wouldn't end a sentence in a preposition!)
I am assuming it is a stove or oven?  Thanks, hope you are doing well, Lu

[KirkM]

This doesn't exactly address your question, but I got this from Wikipedia:

"Persons with implanted cardiac pacemakers or other electronic medical implants may be advised by their doctors to avoid proximity to induction cooktops and other sources of magnetic fields. Radio receivers near the unit may pick up some electromagnetic interference."

Electromagnetic interference to electronic devices is different than metal absorbing enough electromagnetic current to cause inductive heating.

Since the implant is a ferrous metal, the magnetic field could affect it.  However, in my completely non-expert opinion, the fact that there is always going to be at least a foot or so between you and the coil, plus the implant is insulated by 4+ inches of skin, muscle and tissue, it probably would be unlikely that enough of the electromagnetic field could get through to actually get your device to heat up.  However, you should probably avoid sprawling out on the induction surface and cranking it up to high.

Again, just my non-expert opinion.

[David]

Dear Lopsided,

Me and the Mrs. like to jump on the "hob" every once in a while and turn up the heat.
I surely hope I won't have a problem after I get my BHR this month's end.

Curiously signed,
David

[KirkM]

I knew that was coming and I guessed it would probably be David...

[Lopsided]

Kirk and David,

Thank you for your replies. I am trying to keep this subject on a serious note, even if that is difficult for me. My wife and I find that using the bed is better for generating lines of magnetic flux during the night, however that might just be our own peculiarity.

Lu,

I am pleased to hear from you. You do not post often, so I hope you are well. I do realize that the English language originates from the United States, and that Shakespeare himself just pretended to be English to get publicity. A 'hob' is the top part of a cooker that we put the pans of food on to get hot.

Thank you,

Dan the Lopsided

[David]

Lop, can't resist an attempt at a little levity...
Any type of shield/apron out there to alleviate any of your concerns?
Your friend,
Cheeky Monkey David

[hernanu]

I think, Lop, that the induction works by inducing a magnetic field that in turn induces electric fields in the cooking surface, heating it. The magnetic fields are directed, so don't greatly overlap outwards, especially if you use the right sized pan for the hob.

To lessen extraneous magnetic fields (and cook more efficiently), use flat bottomed pans, without dings or dents and make sure it's covering the hob completely. Don't use metal cooking utensils. I think there are pans that are made for induction cooking, maybe those would be good.

Even with all of that, some extraneous fields may be created, but the advice is to stand 5-10 cm away from the hob itself. That's sufficient to stop any impact, and a minimal one at that.

As to the hip, unless you're sitting on it, I would think you'd be fine, but whatever winds your clock  :D

Here's some info from a good source:

http://www.bag.admin.ch/themen/strahlung/00053/00673/03156/index.html?lang=en

[Lopsided]

Hernan, that is an interesting link. It does however say 'The best pans to use are the ones supplied with the hob.' I did not get any pans supplied with my hob. Also, it says 'Appropriate pans: Pans which are suitable for induction hobs' and 'Inappropriate pans: Pans which are not suitable for induction hobs'.

It does seem good to cook with, and is easy to clean.

My cousin put some food in a metal dish in her microwave and ruined the microwave. Good thing I cannot get my resurfaced hip in the microwave. If she comes to visit, I will have to explain to her not to put the microwave on top of the induction hob.

D.

[hernanu]

Yup, got a cousin like that.  ::)

[Tin Soldier]

What happened to my dorky physicist post?  I thought for sure I responded to this yesterday.

Can you put a piece of stainless near the hob (about as close as your hip gets) and see if it heats up?  If it doesn't, then you probably aren't getting any energy imparted to your hip.  Specifically the alloy you want to use should approximate the CoCrMo alloy we have in our hips.  Might be pretty hard to find that alloy.  4140 CrMO might be the closest you could find, say a decent bike frame.  I don't know the various metals concentrations in that alloy or in stainless, but you could look it up.  For comparison, the BHR and I suspect the C+ and others have a composition similar to the BHR alloy which is 70% Co, 20% Cr, 1% Fe, and a few others less than 1% (McMinn's Modern Hip Resurfacing).  I sort of doubt you'll see any temperature change, but it would be kinda fun to do.   

[FlbrkMike]

From what I understand the BHR alloy is designated as ASTM F75 (click here for a very complete description) ISO5832-4 (click here for a large list of implantable metals), also known as Co-28Cr-6Mo Casting Alloy.

28% chromium, 6% molybdenum, a bunch of trace metals less than 1% (including iron and nickel) and the balance (about 74%) cobalt.  Cobalt is considered a "ferromagnetic" metal because it exhibits magnetic properties similar to iron.

Conclusion:  Don't sit on the hob while the heat is turned on.

[Anniee]

Well guys, I really appreciate all this technical info!  I am planning on replacing my stove with an induction one pretty soon - I will now remember not to get up on it while it is in use.  I assume sitting or laying on it while it's not in use would be OK?  Just in case I get the urge...

[Lopsided]

Although you might say that in jest Anniee and Mike, if you lift a pan full of hot food off of the surface while it is sill powered up and put your hand on it (the induction surface not the pan), you will not burn yourself. I am sure you will not sit on it, but it is useful to wipe the thing clean with a cloth while you are still using it.

I will try Tin's suggestion with a piece of scrap stainless steel, and see how close I can hold it to the hob until it starts to warm up. Unfortunately I do not have a convenient bike frame.

I do not wear jewelery, but what happens to someone cooking who is wearing a ring. I imagine most people do not take their rings off to cook. Does your finger get hot? I suppose gold is not ferromagnetic.

[Tin Soldier]

I'm not sure it's worth messing around with stainless or chromolly, neither of them have Co in them, at least nothing like the Co in a hip.  Thanks FlbrMike for the ASTM standard.  That's pretty sweet, they even have the Rockwell Hardness, exciting stuff.  I was going to say that all metals have some magnetism, but Co certainly has more than most and it depends on the crystal structure, which will depend on the treatment process also.  Maybe next time we see our surgeons we should ask for the floor model and pull a magnet out of your pockets and see what happens.  I put a rare earth magnet up to my hip once and didn't feel any weird sensations.     

[FlbrkMike]

Lop, I don't think you should have any problems.  The induction cooker generates a rapidly oscillating magnetic field, which induces a high power, but low voltage, current in the cooking vessel which acts essentially as a resistance heater.

The magnetic field dissipates rapidly with distance from the induction coil.  That's why the cooking utensils used must have flat bottoms.  So, even a few inches away from the coil you would probably feel no heating effect.

[Lopsided]

Good thing the missus does not have a flat bottom then.

What about the mercury fillings in my teeth then? I have got a gold capped tooth too. I have also got a porcelain capped tooth which was a lot cheaper and feels much more comfortable than the gold tooth, but this might not actually be pertinent to a hip resurfacing site.

Anyway, to get back on track, I think it is better to let the wife do the cooking more often than not, and as religiously as I do my PT, I will will continue to refuse to do the washing up. I think it is this resolve that I show in the kitchen, that helped me in my speedy recovery from the operation.

Have I gone off track again?

[hernanu]

Good thing the missus does not have a flat bottom then.

What about the mercury fillings in my teeth then? I have got a gold capped tooth too. I have also got a porcelain capped tooth which was a lot cheaper and feels much more comfortable than the gold tooth, but this might not actually be pertinent to a hip resurfacing site.

Anyway, to get back on track, I think it is better to let the wife do the cooking more often than not, and as religiously as I do my PT, I will will continue to refuse to do the washing up. I think it is this resolve that I show in the kitchen, that helped me in my speedy recovery from the operation.

Have I gone off track again?

I think it is a meritorious thing to take one for the team like that, and surely goes against your better instincts to avoid helping in the kitchen, so as to better heal  ::). My admiration is boundless.

[Anniee]

You guys make me laugh - thanks!!!