Car fire started by button cell battery?

[Someone]

3 x LR44 or AG13, so a 1/3 to a 1/4 of an AA which is still in the plausible range given the above consumer AA's have more than enough energy to produce fire (despite protection).

"X can start a fire, so 1/4-1/3X can also start a fire". This is nonsensical.

That would be engineering, on you know, an engineering forum where you are choosing to post. How much energy can a AA dump? dozens of joules, is 1/3 or a 1/4 of that enough to make flames? yes.

Perhaps you'd like to claim maths is forbidden?

[55pilot]

What datasheet?

From reply #13 above: https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdf

[IanB]

Reading would be easier if you didn't use a low contrast font colour....

People read what they want to read and disregard the rest.

AVGresponding does not wish their posts to be read. I comply accordingly, and skip over all posts in that funny colour and font without looking at them.

[coppercone2]

you know if a battery cover falls off and a hamburger aluminized wrapper gets in there I can see it causing a problem

[amyk]

I cannot find UN 38.1 documents for AG13 batteries after a quick search. That would describe the short circuit conditions of the battery
Nor ESR. I found one claim that it's ~5 Ohm, so let's work with that.
4.5V 15 Ohm source means that there is 337mW power available for the electronics. I can make electronics safe with this much power, it's very low. Meaning I can design you eg. a sensor that's mounted inside a gas tank, and it's going to be safe. But let's work from the other way.
It's a children book with built in battery. Paper's autoignition temperature is ~230C. Probably they just chucked the electronics in between paper pieces, with some loose wires, and it's made from single side phenol PCB. And made a mistake while assembling it, wire is not properly isolated. Take a small part, like an 0402 resistor, apply 300mW to it. It goes from 70C to 150C with 63mW, about 1.2K/mW, suddenly your part is over 400 Celsius hot, enough to set paper on fire.

You are neglecting the thermal loading of the paper on the resistor.  I would be surprised if the paper could itself get to 400C in a local spot to support combustion with that resistor alone.

Don't forget that combustion also requires oxygen. Also, in my experience regular book paper is difficult to ignite with things other than an actual flame, especially if the heat source is small; it tends to just carbonise instead.

On the other hand, if the paper was soaked in something like ethanol-based hand sanitiser...

[mikeselectricstuff]

I can't see any immediate/easy fire risk.

Hint: One of them is black, the other red. They go directly to the battery.
Also these things get chewed on, thrown around, and who knows what else.

But they would have to break through the plastic case, break the insulation of both wires, then the wires would need to contact each other.  Even then, I'm not sure such a modest current (maybe 0.7 Amps), could readily cause a fire.

Or just a strand of a stripped end shorting at the PCB end. These wires will be crazy thin to start with.

[tszaboo]

What datasheet?

From reply #13 above: https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdf

Thank you, I was perfectly able to read the datasheet. It's a datasheet for a LR44 battery, while the article states the book has an AG13 battery in it. Which is different chemistry.

[AVGresponding]

3 x LR44 or AG13, so a 1/3 to a 1/4 of an AA which is still in the plausible range given the above consumer AA's have more than enough energy to produce fire (despite protection).

"X can start a fire, so 1/4-1/3X can also start a fire". This is nonsensical.

That would be engineering, on you know, an engineering forum where you are choosing to post. How much energy can a AA dump? dozens of joules, is 1/3 or a 1/4 of that enough to make flames? yes.

Perhaps you'd like to claim maths is forbidden?

I'd like to claim that you haven't proved it, you've just guessed at it. That's not engineering.

What datasheet?

From reply #13 above: https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdf

Thank you, I was perfectly able to read the datasheet. It's a datasheet for a LR44 battery, while the article states the book has an AG13 battery in it. Which is different chemistry.

In counter-argument, they are the same size, and the average person is likely to replace dead ones with the cheapest option they find on/in Amazon/ebay/a local shop, so we don't know if the ones in the e-book in the fire were alkaline or silver oxide.

I just measured the short-circuit current of a new LR44 at 0.7A - not totally implausaible that this ( or 2-3 of them) could start a fire

Over what duration?

[Siwastaja]

I just measured the short-circuit current of a new LR44 at 0.7A - not totally implausaible that this ( or 2-3 of them) could start a fire

Over what duration?

We can guess that Mike did not use an oscilloscope and pulse generator for the test, but instead just shorted the battery with a multimeter and looked at the screen. Which makes it in ~1 second timescale where the AC (capacitor) effects of the cell are irrelevant. Actually cells heating up reduces their ESR so current would even rise higher for some time - seconds, tens of seconds(?)

0.7A * 4.5V = 3.15W and this in timescales of at least tens of seconds.


I do agree that terms LR44 and AG13 are widely and synonymously (even if incorrectly) used to describe the form factor, most probably the chemistry would be either Alkaline or some of the lower-voltage primary lithiums like lithium iron disulfide.

[tooki]

Reading would be easier if you didn't use a low contrast font colour....

People read what they want to read and disregard the rest.

I’ve been asking you for years to stop using your stupid custom font and color, which reduces legibility by overriding the defaults. (Which means that when the user adjusts their browser to make the default readable, your settings override it to an extent.)

I’m glad someone else has called you out on this nonsense. I don’t understand why you can’t just leave the damned default text formatting. (In the past you’ve said it’s to improve legibility, but it does the exact opposite.)

[Someone]

3 x LR44 or AG13, so a 1/3 to a 1/4 of an AA which is still in the plausible range given the above consumer AA's have more than enough energy to produce fire (despite protection).

"X can start a fire, so 1/4-1/3X can also start a fire". This is nonsensical.

That would be engineering, on you know, an engineering forum where you are choosing to post. How much energy can a AA dump? dozens of joules, is 1/3 or a 1/4 of that enough to make flames? yes.

Perhaps you'd like to claim maths is forbidden?

I'd like to claim that you haven't proved it, you've just guessed at it. That's not engineering.

I checked some standards for safety limits on energy and some battery data sheets, and presented the maths. Engineering building upon the established methods and standards. You think 10 joules cannot start a fire and is benign? Perhaps show us the supporting documentation that says so.

[MK14]

I can't see any immediate/easy fire risk.

Hint: One of them is black, the other red. They go directly to the battery.
Also these things get chewed on, thrown around, and who knows what else.

But they would have to break through the plastic case, break the insulation of both wires, then the wires would need to contact each other.  Even then, I'm not sure such a modest current (maybe 0.7 Amps), could readily cause a fire.

Or just a strand of a stripped end shorting at the PCB end. These wires will be crazy thin to start with.

On reflection, I agree with you.  That is a very good point.  That sounds very plausible.

Now, is that 0.7 Amp back of envelope, ball-park measurement, enough to potentially cause a fire?

Looking into, the minimum current needed to cause an electrical fire, finds the following, professional/academic looking, interesting (free/open) paper, on the subject:

https://www.mdpi.com/2571-6255/5/6/201

Which seems to mention (but it refers to another person or source of information), that as little as 4.5 Volts (coincidentally the nominal battery voltage, of this threads situation, 3 x 1.5 Volt AG13 batteries = 4.5 Volts), and 300 milliamps (which seems plausible, since you already measured a short-circuit current of 0.7 Amps), may be able to cause sparking (maybe even arcing), and hence be an ignition/fire risk.

Also, on reflection, I've realized that my assumption, that the wires were pure copper, plastic insulated ones.  Could be wrong.  The Chinese (other countries could have been just as bad), may have cheaped out on these wires, possibly being a different metal, or copper coated metal of some sort.

Hence the wires, could, unlike copper, have higher resistance, be more susceptible to breaking (brittle, hence sparking/arcing etc), possibly even being flammable (aluminum comes to mind).

So, I now think, that it has become more plausible, that those 3 x AG13's (or LR44's, if that is what they were replaced with), may be able to be the cause of that fire.

Practical demonstration.  This video, less than 2 minutes long (if inpatient, at around 38 seconds into the video, it is shown), seems to show a low voltage and current, set fire to the ends of some thin wires.  I'm not sure of what PP3 battery type they were using, or how much more current, it can make, as a result.

[Someone]

Or just a strand of a stripped end shorting at the PCB end. These wires will be crazy thin to start with.

On reflection, I agree with you.  That is a very good point.  That sounds very plausible.

Now, is that 0.7 Amp back of envelope, ball-park measurement, enough to potentially cause a fire?

Sure is, having some time to play around I tested this directly.

4.5V 0.7A supply, connected to a 10ohm resistor with very fine copper wires.

0402 glowed bright red and let off a puff of smoke as it desoldered itself, still measures in the ballpark
0805 glowed bright red and let off a puff of smoke (the characteristic ceramic/resistor smell) but stayed attached much longer.

SET PAPER ON FIRE

case closed

[Someone]

Only needed 300mA

[Psi]

You don't need much energy to start a fire if you have the right conditions.

I can totally see a toy made of flammable plastic catching fire from coin cells.
The size of the hot spot can be very small if everything is aligned perfectly.

Usually you wouldn't get that alignment which is why this sort of fire from coil cells is so rare.
 
You'd need exactly the right placement to get the tiny hot spot to catch the plastic alight combined with enough air through the inside to keep the fire growing.
Maybe a tiny sliver of 'flash' that's against a component on the PCB right next to a speaker grill that's full of holes.  The sliver catches on fire, and that manages to couple to the plastic between all the holes in the speaker and that spreads to the entire device.

[Monkeh]

What datasheet?

From reply #13 above: https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdf

Thank you, I was perfectly able to read the datasheet. It's a datasheet for a LR44 battery, while the article states the book has an AG13 battery in it. Which is different chemistry.

LR44 and AG13 are the same chemistry - don't get confused with the silver-oxide version.

[Siwastaja]

For example, manufacturer might have decided to save $0.001 each by specifying any plastic for injection molding, instead of some UL94 (or whatever, I don't remember the standards that well) rated material. It is also well possible that the relevant legal standards allow doing this because they consider available power level small enough. (See PIS (potential ignition source) and their classifications based on available power.)

But as Someone demonstrated, even power levels below such requirements pose fire risks, just that the risk is probably smaller but still non-zero. So even if you have a totally standard compliant, legal device, a "freak accident" can still happen, that's life.

[Siwastaja]

case closed

_{Where's the peer reviewed scientific publication???}

[IanB]

LR44 and AG13 are the same chemistry - don't get confused with the silver-oxide version.

Technically, the AG in AG13 should mean it is silver oxide composition (Ag being the chemical symbol for silver), however the market has ended up confusing them, and nearly all such cells of this size are now alkaline, presumably because the alkaline version is much cheaper to produce, and few products really need the special properties of silver oxide.

Similarly, SR44 should be silver oxide and LR44 should be alkaline, but once more, marketing has confused the issue, and now you see "SR44 alkaline", which is daft.

Nevertheless, silver oxide cells are never going to be found in consumable products like greetings cards or children's toys.

[Someone]

But as Someone demonstrated, even power levels below such requirements pose fire risks, just that the risk is probably smaller but still non-zero. So even if you have a totally standard compliant, legal device, a "freak accident" can still happen, that's life.

My reading of standards and papers suggested 10 joules, I ended up in benign conditions with around 5 joules to flame (no forced air/oxygen or diethyl ether soaked paper needed). Always nice when the calculations arrive on target.

[Monkeh]

LR44 and AG13 are the same chemistry - don't get confused with the silver-oxide version.

Technically, the AG in AG13 should mean it is silver oxide composition (Ag being the chemical symbol for silver)

Except that's an SG13. I've never once seen an AG marked cell which is silver-oxide. Probably because the A stands for alkaline.. Technically, there is no standard (that I've ever seen) so you're simply assuming there's a correlation between two as good as random letters in a part number and a chemical element.

[IanB]

Except that's an SG13. I've never once seen an AG marked cell which is silver-oxide. Probably because the A stands for alkaline.. Technically, there is no standard (that I've ever seen) so you're simply assuming there's a correlation between two as good as random letters in a part number and a chemical element.

Yes, that seems true. The silver oxide cells are typically marked as 303, 357, or SR44. They will clearly say "silver oxide" on the packaging, rather than alkaline.

There is a presumed standard that LR44 is alkaline, and SR44 is silver oxide.

Here's an actual example of a silver oxide cell:

https://www.duracell.com/en-us/product/coin-button-303357-battery/

[Siwastaja]

It's safest to treat these letter-number combinations as physical form factors only, and verify the chemistry separately from the packaging/datasheet.

[CatalinaWOW]

Just for a sanity check.  Under fairly ideal conditions (dry fine tinder etc.) it is possible to start a fire with a single spark from a flint/steel combination.  Assuming that the the grit of steel shaved off and heated is roughly a 0.5 mm cube, and giving it white hot temperature, the thermal energy in the spark is on the order of 0.5 joule.  I suspect that these sparks are actually quite a bit smaller than 0.5 mm so the estimate is conservative. 

  So any of these batteries contain plenty of energy to start a fire under ideal conditions.  The question then devolves into two parts.  Can the energy be extracted rapidly enough from the battery and how close to "ideal" conditions are realistic. 

The first question is half easy.  From data sheets and the experiments reported here something on the order of a half watt can be extracted from these cells.  How hot that can make something depends on the degree of thermal isolation.  Getting from the ambient temperature up to the greater than 200 degree ignition temperature of common materials requires something like 300 deg/watt thermal isolation.  High, but not impossible.  And there is always the possibility that this is a two factor event.  A cell phone, or baby bottle or something else had raised the ambient temperature to quite a bit above the nominal 23 C.

The second question is harder to pin down.  A list of materials with low ignition temperatures includes quite a few that might be found in such a device.  What can't be easily determined is whether any of those likely candidates could have been in a configuration that allowed them to be heated enough to ignite.  Anyone who has ever built fires knows that configuration is at least as important as composition.

Rubber, Butadiene                                   155
Diethyl ether                                           160
Acetaldehyde                                           175
Rubber, Styrene butadiene - Styrene 24%   182
Rubber, Butyl                                           185
Ehtyl cellulose                                           188
Polybutane                                           188
Rubber, Natural - Low refine                   191
Polypropylene                                           201
Diesel                                                   210
Fuel Oil No.1                                           210
Kerosine                                                   210
Jet A-1 fuel                                           210
n-Heptane                                                   215
n-Octane                                                   220
Gun Cotton                                           221
n-Hexane                                                   225
Polyethylene                                           226
Polyethylene glycol                                   226
Polystyrene                                           226
Peat                                                           227
Wood, Pine - Powdered                           232
Paper                                                   233
Cyclohexane                                           245
Nitro-glycerine                                           254
Fuel Oil No.2                                           256
n-Pentane                                                   260
Phosphorous - Amorphus                           260
Fuel Oil No.4                                           262
Polymethyl methacrylate                           265
Cotton cloth                                           267
Gasoline                                                   280
Rubber, Styrene butadiene - Styrene 85%   280
Rifle Powder                                           288
Nylon 11                                                   289
n-Pentene                                                   298
Rubber, Butadiene - Vulcanized                   298
Bituminous coal                                           300
Wood                                                   300
Acetylene                                                   305
Nylon 6                                                   329
Polyvinylidene Fluoride                           330
Rubber, Natural - High refine                   331
Charcoal                                                   349
Nylon 6/9                                                   356
Ehtyl Alcohol   365

[Someone]

Getting from the ambient temperature up to the greater than 200 degree ignition temperature of common materials requires something like 300 deg/watt thermal isolation. High, but not impossible.

Yes, it does require some marginal design but x00 Rth values (degrees C/W) are easy enough to find:
https://www.vishay.com/docs/53048/pprachp.pdf