If a drone falls in a forest does anybody care...? Fire risks of unretrieved drones.

[Vague Nerd]

I have searched and searched and I cannot see that anyone has addressed this head on, but pardon me if there has been some dedicated discussion on this topic.

Preamble: I live in BC (Canada) and do a lot of backcountry camping and hiking. I have an Advanced Operations Drone Pilot Certificate. I make a point of trying to fly legally, and there are lots of great places to fly in my province. But I encounter a lot of very rugged mountainous terrain in the places I go. I try to fly in places where I could retrieve my drone if it crashed, but one cannot account for EVERY bad outcome or calculate EVERY improbable crash.

The issue: what happens if my drone ends up on a mountainside or, worse, in a tree and I just cannot retrieve it? Is there a risk of the LiPo battery causing a fire at some later time? I guess for that matter it doesn't even need to be in a remote forest, I have read lots of stories in this forum about heroic tree recoveries from people's own property-- but what if you cannot get the darn thing down? At some random time in the future is it possible or probable that those LiPro batteries are going to give up the ghost and explode (we've all seen the videos) into flame throwing chaos. Our province (and many other regions in the world) suffered absolutely catastrophic forest fires last year... I guess if I could not retrieve that drone I would just be worrying about a ticking bomb out there waiting to go off.

Any thoughts? Thanks in advance.

 

[Skywatcher2001]

This was/is a great title and DEFINITELY a valid subject. There is a risk of ignition. We discussed it a bit "HERE" . . . As you mentioned, many drones are lost and never recovered. A tree crash softens the landing (somewhat) but the risk of internal battery damage and ignition (at a later date) is still there.

I'll be following this thread . . .

 

[Phantomrain.org]

The only risk is a Puncture to the Battery as we have seen that will set off a ungodly amount of sparks and black Smoke. Those batteries do have a thick casing on them and even a fall from a tall tree is not likely to break one open.

There is however the threat of the wind causing it to fall one someone , so best to try to get it down anyway possible.

Phantomrain.org
Gear to fly in the Rain. Land on the Water

 

[slup]

...The issue: what happens if my drone ends up on a mountainside or, worse, in a tree and I just cannot retrieve it? Is there a risk of the LiPo battery causing a fire at some later time? ... At some random time in the future is it possible or probable that those LiPro batteries are going to give up the ghost and explode...

In that scenario the risk is very minimal ... this as the drone most probably will remain powered after the touch down & will slowly discharge the battery until it shut's off, after that the self discharge will take care of the little that is left. The remaining stored energy will after a while be so low that I honestly doubt it will combust even if it gets punctured in some way.

Most fires of Lithium batteries occur during charging or discharging more current than the battery is rated for, “short circuit current”.

In a scenario where you crash hard, breaking a nearly full battery open ... then yes, that might set it on fire.

 

[Vague Nerd]

Thanks everyone. I guess to add nuance to my post/ question: I am not so much worried about a catastrophic crash that punctures the battery... Well I guess I am worried about that too (nod to PhantomRain), but that would create a fire that I could see and potentially do something about. I am concerned about leaving the drone in the wilderness and wondering about whether the batteries could do or not do harm long after the fact. @slup, is it the case that a discharged battery is unlikely to create a fire hazard... I just don't know. I am thinking that even the Li that is still on board after months or even years of sitting out in the rain and the snow, freezing and thawing, and cycles of getting wet and drying out, would crack the casing and once the Li was exposed to O2 could combust. I really don't know I am not a chemist or a materials engineer.

I suppose the only way to test this would be to take new intact batteries at various levels of charge and put them outside and see what happens over hours, days, weeks and months. Great PhD thesis...

 

[Phantomrain.org]

Many drones have been found years latter , battery intact both in the sky and under water.
Because of this there seems to be no harm in a battery left out for years in tact, outside or under water .

I was throwing a Phantom 4 Battery away that I had had for years and it still was explosive once punctured , so that really is the only risk and DJI makes the casing pretty hard on the Mavic series drones now.

Phantomrain.org
Gear to fly in the Rain. land on the Water.

 

[slup]

...is it the case that a discharged battery is unlikely to create a fire hazard...

A fully discharged battery will never ever cause a fire hazard, that's why it's important to fully discharge a battery before you dispose of it in a suitable way ... so it wouldn't crack open during the handling taking care of it & set the place on fire.

...getting wet and drying out, would crack the casing and once the Li was exposed to O2 could combust...

That's not how the electrolyte works ... it can be highly corrosive, but as said above, without being charged it will not cause any combustion.

 

[Vague Nerd]

A fully discharged battery will never ever cause a fire hazard, that's why it's important to fully discharge a battery before you dispose of it in a suitable way ... so it wouldn't crack open during the handling taking care of it & set the place on fire.


That's not how the electrolyte works ... it can be highly corrosive, but as said above, without being charged it will not cause any combustion.

Thanks, this is really helpful and getting me much closer to an accurate risk assessment.

 

[dronerdave]

If the crash causes a heavy enough impact to short a connection between the battery and the drone, I could see a fire possibly occur. Same if the battery cell is punctured. It's still rare but I've seen LiPo fires due to crashes more than once. In some RC airplane crashes it's common for the battery to eject and sometimes you'll never find it. But I've yet to see a LiPo burn at our flying site even after the battery has sat in tall grass for a year. Not saying it can't happen, just very rare. One of the guys lost his drone in a field of oats. We looked for it for hours and even with the location feature showing we were close, it stayed hidden and was never recovered. Probably eventually ended up in a hay bail.

You are simply responsible for your flight and if a fire happens because of your actions, it's just part of the risk in flying RC aircraft. How it would be handled in court is anybodies guess provided it even come to that.

 

[Chaosrider]

In that scenario the risk is very minimal ... this as the drone most probably will remain powered after the touch down & will slowly discharge the battery until it shut's off, after that the self discharge will take care of the little that is left. The remaining stored energy will after a while be so low that I honestly doubt it will combust even if it gets punctured in some way.

Most fires of Lithium batteries occur during charging or discharging more current than the battery is rated for, “short circuit current”.

In a scenario where you crash hard, breaking a nearly full battery open ... then yes, that might set it on fire.

I've had two cases of a drone getting stuck in a tree, or lost (later found). In both cases, the camera continued to record until the battery died.

I'd be interested to see real statistics or analysis about this, but I expect that the fire risk is always low, and gradually drops to zero as the battery discharges over time.

 

[Vague Nerd]

Thanks everyone for thoughtful and insightful replies. My mind is put more at ease, and I think this information allows people to manage and stratify risk while doing what we love.

 

[Vague Nerd]

I've had two cases of a drone getting stuck in a tree, or lost (later found). In both cases, the camera continued to record until the battery died.

I'd be interested to see real statistics or analysis about this, but I expect that the fire risk is always low, and gradually drops to zero as the battery discharges over time.

Thanks. And agreed, I would love to see actual analysis on this... maybe someone will take my suggestion around doing a PhD thesis...

 

[VenomXts]

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[EpicFlight]

In that scenario the risk is very minimal ... this as the drone most probably will remain powered after the touch down & will slowly discharge the battery until it shut's off, after that the self discharge will take care of the little that is left.

Just picking one nit: Not correct. Self discharge only applies to a battery over roughly 60%, which will bring it down to safe storage levels after a few days.

A discharged battery will not self-discharge further, into damage territory.

 

[slup]

...A discharged battery will not self-discharge further, into damage territory.

It most probably will, try it for your self, drop your drone powered in the woods where it will go to 0% & shortly after it will turn itself off. Then leave it there for a year ... chances are pretty substantial that it's stone cold dead when you go & pick it up

That's why DJI recommend a full charge cycling each 3 month & back to storage voltage during long term storage.

 

[EpicFlight]

It most probably will, try it for your self, drop your drone powered in the woods where it will go to 0% & shortly after it will turn itself off. Then leave it there for a year ... chances are pretty substantial that it's stone cold dead when you go & pick it up

Agree, but not because the self-discharge kicks in, as you said. Or did I misunderstand?

After 1 year, the battery may or may not charge. Depends on what it's been through.