Lipo fire

[ChrisB]

Confusing some phones say they have lithium ion polymer in them so maybe a hybrid type?

[Mark_T]

Confusing some phones say they have lithium ion polymer in them so maybe a hybrid type?

Lithium Ion Polymer is just the full name for what we abbreviate to 'Lipo'.

You won't find a Lithium Ion battery in a cell phone these days as they are metal cased and tend to be round in form-factor. The thin flat packs need to be polymer based.

With the various air crashes we need to separate fires involving primary lithium cells (non-rechargeable) and those where lithium polymer cells are suspected.

The fires involving lithium primary cells are the really bad ones due to the high lithium content of these cells.

[cjcj1949]

The polymer refers to the electrolyte. Lithium Ion was solid but low on current capability. Lipo is liquid. The cells in consumer items were solid but have now had some liquid added to become a half breed. The source seemed reliable but it was not a proper technical data sheet. There have been a few recalls of laptop batteries but not a lot of incidents. Quality control and testing seems non existent in the lipos we buy.

[trillian]

I think if you worked out how many LiPos are in service in RC helis vs the amount of fires I would bet the percentage is very low. Having said that it perhaps doesn't hurt being reminded we cannot get too cozy with these things.

In this case if it was a turbine then the LiPo would be either the one that powers up the turbine to start it and cool down or the RX power. Without knowing any more detail, it could have become overheated or something and whatever the case it wasn't just sitting in a box minding it's own business and spontaneously combusted.

I'd be interested to know if the crash analysis on those two cargo planes was able to conclude anything for certain. In general it seems the vast majority of LiPo fires happen either as a result of a puncture or other trauma or a charging error.

[Mark_T]

I'd be interested to know if the crash analysis on those two cargo planes was able to conclude anything for certain. In general it seems the vast majority of LiPo fires happen either as a result of a puncture or other trauma or a charging error.

Nothing conclusive.

The problems are not normally associated with our secondary type cells that are at risk of puncture, it is normally the primary cells which are typically metal cased so it is not puncture but shorting or overheating that are the big risks.

The problem with these primary cells is that even if they are not the initial cause of the combustion, once the fire gets to them the result is something that cannot be extinguished with any means currently available in flight.

[cjcj1949]

Perhaps we need the Monty Python soft fruit protection measure. Perhaps ejection isn't such a good idea, but surely the reaction can be contained by correct packaging? Can't they use the equivalent of ammo boxes? I'd like to know what volume of gas gets generated and what pressures are practical in an enclosure. Liquid nitrogen is cheap and should slow the reaction down.

[Mark_T]

Perhaps ejection isn't such a good idea, but surely the reaction can be contained by correct packaging? Can't they use the equivalent of ammo boxes?

The problem is always about weight. You can build a suitable enclosure but the costs of shipping would then be completely prohibitive.

Slowing things down doesn't help all that much when you are at 30,000 feet and an hour away from anywhere you can land, if you can't put it out completely it still ends the same way.

A lot (most?) cargo only planes don't even have a fire suppression system in the cargo hold as they rely on de-pressurization as the primary fire control method. Even those that do have a fire suppression system fitted have been shown to be ineffective in dealing with primary lithium fires. This is why they can no longer be shipped as freight on passenger aircraft.

The FAA investigations recommended that when these cells were shipped as cargo they should be shipped in FAA approved fire-resistant containers, problem is testing shows the currently available containers are ineffective for this type of cargo, but there are some promising new candidates apparently ...

Not sure I'd be all that happy if I was a cargo pilot these days.

[cjcj1949]

Slowing the reaction down could well stop it. All reactions rates are temperature dependent and at really low temperatures it may well stop. I expect they've thought of that though. Same sort of thing with explosives, but that would make bomb disposal easy, so that can't be right. Perhaps ejection is a viable alternative. Better than losing the crew. Just needs a major redesign of the airframe. Could they be packaged in long tubes? If they were led to the back of the aircraft they could be vented quickly to the outside and wouldn't need to contain much of a temperature rise.

[Mark_T]

I think they will go for the easy solution, either bring the risk inside acceptable limits through better container design, or just stop accepting them for air freight completely.

Once again, this is primary cells we are talking about, cells like our Lipo packs are considered to just be a 'normal' fire hazard.

[scallybert]

[...]cells like our Lipo packs are considered to just be a 'normal' fire hazard.

And, if I've read the thread correctly, not disimilar to the laptop / camera / phone batteries that passengers are very keen to carry on with them.

[Mark_T]

And, if I've read the thread correctly, not disimilar to the laptop / camera / phone batteries that passengers are very keen to carry on with them.

Correct.

The only real differences are the size of our packs and the fact that they are not installed in a device which is why they are subject to specific limitations when we carry them on-board passenger aircraft.