Post By rolygate
Exploding Mods Update - February 2012
Here is a Feb 2012 update to reflect current events, and to ensure that people understand the current ECF view.
Below, some incidents are described that involve XL specials, called APVs or mods, with two lithium batteries inserted in series to provide high voltage. These large metal tubemods* with stacked batteries are the ONLY type of device implicated in recent incidents, and cautions mainly apply to these devices.
Other types of e-cigarette ARE NOT affected.
Single-battery APVs are not affected.
Regular e-cigarettes (minis and mid-size models) are not affected.
*Metal tubemods with full electronic control are not implicated since none has ever experienced one of these events. Only mechanical and basic electrical metal tube devices that were used with two batteries have been involved.
In early 2012 there have been two recent events, one in Colorado, and one in FL that was widely reported in the world media. These incidents are not helpful to the e-cigarette community. The two most recent events appear to have been serious, with the victims in ER after suffering extensive facial injuries.
This unfortunately shows that the situation is not improving, probably simply because the number of APVs being sold is increasing dramatically.
Here are some itemised points of note:
- ECF has had a total of around 8 reports of 'facial explosions' and 'rocket-mode fails' now. However, asking around vendors, many of them do know of events that were not reported on ECF and where teeth were knocked out or similar. This leads us to think there may have been about double this number - perhaps 15 blowups in total.
- All explosions reported so far involve metal tubemods with two batteries in series.
- Full electronic control metal tube APVs are not implicated (none has ever suffered a failure of this type). Only mechanical and basic electric metal tubemods that accept two batteries have experienced an explosive failure.
- Boxmods are not implicated. Apart from electrical factors such as non-conductivity of a plastic or wood body (and so no risk of a short-circuit), there is the likelihood that gas will escape from a squonk hole, and/or the lid/door will simply blow off at the first outgas stage before the violent second-stage outgas.
- Single-battery units are not implicated, as far as we are aware at ECF.
- Regular e-cigarettes are not implicated, as far as we are aware at ECF (minis like the 510 and KR808, and mid-size models like the eGo/Riva/Tornado).
- The explosions started a long time ago with early 2-cell devices, and still occur with the latest 2-cell models.
- All lithium battery types, either single or in pairs, can suffer from a meltdown including heat, gas and flame. There are no exceptions to this. There is no such thing as a 'safe' lithium battery of any kind. There is a difference between meltdown and explosion though: the explosions causing injury always happen to stacked batteries in metal tubemods.
- The safest battery is the largest battery, because one of the factors that causes the explosions is that the batteries are too small for the job. Smaller batteries ARE NOT safer. Even a little RC123 cell (16340) may have around the same explosive power as a grenade of the same size.
- Virtually all reported explosions have involved paired RC123-size cells: that is, 16340 size batteries used in series, aka 'stacked'.
- Any/every size and type of cell can be reported as involved in a meltdown, since any lithium cell will suffer meltdown if abused and/or faulty.
Some notes on APV safety features
Anyone who has worked in engineering for a few years will know the most basic rule of engineering, sometimes called Murphy's Law of Engineering: if it can go wrong, it will do someday, and several things will go wrong at the same time, and it will be at the worst possible time.
To build an APV without taking this into account (and especially a metal tubemod) is not good engineering - it isn't engineering at all. Murphy's Law means that a safety cutout will fail. It means that two separate safety features will fail at the same time. And finally, it means that to protect the user, some way of preventing injury needs to be incorporated that cannot go wrong because it is a physical feature.
Example: a device with a large hole in it somewhere cannot explode - because it isn't sealed. This sort of measure is needed to defeat Murphy's Law.
In all the reports of explosions we have received where there was some way gas could escape, there was a first-stage outgas lasting a few seconds where hot gas and flame vented strongly from available apertures, followed by a violent second-stage outgas where, if there was not enough vent cross-sectional area to release the gas, the device exploded. Small gas vent holes will not stop such an explosion.
In other cases, there was sufficient vent cross-section, and the second-stage vent resulted in a violent outgas but no explosion. In this case, fires were started when the unit was in contact with furniture or a carpet, as it acted as a small flame-thrower. Also, these cases have included incidents where the second-stage outgas was of such force while escaping in one direction only that the device launched itself like a rocket.
What this shows is that small gas vents are simply a warning device. If they are placed for example around the circumference of the tube body - the ideal position - then the hot gas and flame of the first-stage outgas will burn the holding hand and the unit will be dropped. The explosion then occurs when the APV is on the floor, away from the face.
With no gas vents at all, if the batteries go into thermal runaway, there is no warning and the device can explode in the face.
The ideal design for a metal tubemod would be to have three milled slots in the tube body: three slots, along the length of the body, equally spaced around the circumference, of around 50mm x 4mm or 2 inches x 5/32nds width. This cross-sectional area should allow the second-stage outgas to escape without causing an explosion, and a blowout plug would not be needed.
Update Q3 2012
Blowout plugs (bottom end caps) are not a solution, because they are at the bottom, and because the successful operation of a blowout plug has implications. Batteries can swell when going thermal and can block the tube, preventing gas from venting downward; and when a blowout plug works it can result in the device being driven hard into the user's face. The main issue in any case is pressure at the top end of the tube; and how to dump it without causing facial injury or providing a single gas vent point that causes a rocket-mode event. If pressure builds at the top of the tube, then the atomizer and connector, or the whole top end, can be blown off into the face. This must be prevented at all costs. The only viable option in existing designs* is the provision of large gas vents at the top of the tube. Slots are a good engineering solution because they provide exceptionally large cross sectional area versus the visual impact; they will cover most of the tube body; they are cheap to machine (we had a quote for $6 per unit, to mill 3 large slots, for a production run); and they are the easiest option to fill in, one way or another, for the purpose of prevention of ingress of foreign bodies.
* New designs are a different matter: provision for gas venting can be built-in. For example a corrugated internal liner could be used; or the device could be built from box section stock ('square tube'), which would intrinsically have large internal vent channels.
At late 2012 an APV with large gas vent slots has now been produced with filled slots that are not only hardly noticeable, but that add to the overall design, and which is waterproof to IP65. The slot filler plugs blow out at 20psi. It is also one of the best-looking tubemods out there, so effective safety features do not have to mean the design is wrecked.
Minis like the 510 and KR808 don't explode, even though they are steel tubes. This is because they all have built-in digital monitoring and protection, and a bottom-end blowout plug. Meltdowns do occur but are not common.
Models such as the eGo and Riva are not likely to explode in use because they have integral protection. If they all had end plugs it would also help - those with a bottom-end USB charge facility in effect have a blowout plug. Others have a sealed lower end. As single-cell units, the risk is low.
However they seem to suffer from more meltdowns than any other type, usually while on charge - perhaps because the load on them is generally higher (when using LR fittings for example) than on the minis, and the management circuitry being similar; or due to charger faults. As they seem to fail while being charged, there may also be a conflict between the charger requirements for different models: some may need a protected charger, others may require a 5 volt supply, and if they are used with the wrong type then overcharging may result.
The tiny circuits may have to take 2.5 amps DC, and this is a lot for micro-electronics in a very small package. Failure while on charge is not under discussion here, it does not threaten the user's safety - it is a charger / device quality issue. Owners should also not leave them on charge, as the cheap charging devices used are hardly all likely to have adequate protections. Use of a Li-Po charging sack seems a good idea for these mid-size models, if not for all lithium cell charging.
Mod / battery failure modes
There are three failure modes we know of:
1. Meltdown mode
A battery fails and melts down with extreme heat, flame, and some gas. This can occur to all and every lithium battery type when provoked. There is no type of lithium cell immune to this, all have been reported as failing in this mode. It is simply to be expected, when abused.
Abuse = overcharged by a faulty charger, or overcharged by being left on a cheap charger, or asked to deliver too much current for the cell size, or dropped and damaged, or with an electrical issue but never checked on a meter, or the outer sleeve torn and the cell shorting out to the metal body of the device, or the on/off switch jammed on in a pocket, or something shorted out by keys or change in a purse, or a faulty adapter shorting out - etc. There are a lot of ways to make a battery fail.
2. Rocket mode
This is where the second-stage outgas, which is violent and prolonged, manages to find sufficient vent cross-sectional area to avoid a containment explosion, by for example blowing off the bottom endcap. One of two things can then happen: either the batteries are ejected and may continue to burn independently; or they can swell and jam in the tube. In that case, the powerful gas jet exiting the large hole propels the device away like a rocket. The gas from all lithium battery failures can include hydrogen, methane and ethylene, produced in large volume when some cell types fail, and can ignite with oxygen when there is a heat source of sufficient temperature, which the cell failure often provides. The ignition as the gas combines with atmospheric oxygen and the resulting increase in pressure drives the device away vigorously. In one reported event, two rooms were set on fire when the device travelled through a door.
3. Grenade mode
With no real gas exit of any significant cross-sectional area, the mod explodes at the second-stage outgas. If there were no weak point at all, the casing would fragment like a grenade, since what we have here is basically a pipe bomb: a sealed metal container with an internal fast gas production source. However there will always be one weak point: the atomizer connection. If nothing else blows out, the top end fitting (carto or atty) will be blown off into the user's face.
With a bottom-end blowout plug, this will blow off first. The reaction vector will propel the mod into the user's face with a very fast, short, sharp shock, usually resulting in minor damage. There might be damage to the holding hand, if the end was obscured by the hand at the time.
With the examples of minor facial damage reported by ecig users, and damage done to furniture by the force of an end cap blowing off reported by the flashlight community, we cannot regard the successful operation of a blowout plug as being without implications. Explosions are far more common with flashlights using lithium batteries than with e-cig mods, and have been estimated as occurring as often as 1 in 1,600 units. Lithium cell unreliability appears to be a universal problem.
The flashlight community also report the occasional event of lithium poisoning caused by lithium inclusion in wounds resulting from an exploding flashlight, which we have not seen so far.
All these fail modes have been experienced, and reported on ECF.
Explosions seem to happen immediately after charging, on first use, on the first press of the switch. Every report with full details says this.
With an available gas vent or vents to show it, there is usually a first outgas of several seconds, producing an intense jet of hot gas from the vent/s.
An explosion may then occur (frequently after the user has dropped the unit); or if there is sufficient gas vent area, the outgassing sharply intensifies and a jet of gas strong enough to act as a flamethrower may be produced. It seems a good idea to have dropped the mod by this stage. With no large gas vents, the unit may explode. Two or three small gas vents do not qualify as 'large' vents here, they just do not have enough cross-section to vent the huge volume of gas produced very rapidly. It needs large slots or a hole of maybe 18mm / 3/4".
So that is the basic information we have at this date. As a result, the following advice can be given at this time:
- For ultimate safety, use a single-battery mod.
- For high-voltage, use a single-battery mod with a booster circuit of some kind.
- No APV with full electronic control has been implicated so far, so statistically these appear safe. You might want to play safe, though, and consider one with gas vents.
- Use the best and most expensive batteries you can get. It doesn't seem worth it to economise on batteries. Our opinion is that, at this time, the AW IMR 'red' cell has the best reputation. It is a lithium-manganese 'safer chemistry' cell that does not need the integral protection circuit a Li-ion cell needs. Although these have never been known to explode, no lithium battery, ultimately, is absolutely safe: they will certainly meltdown with plenty of heat and flame if abused; and if they were sealed into a perfectly gastight container, and then made to fail, an explosion might result under those particular conditions.
- We know that using a two-battery metal tubemod is intrinsically more dangerous because these are where the explosions are.
- Using such a unit without large gas vents seems to involve the highest risk.
- You should think very carefully before buying a metal tubemod with no physical safety features.
- APVs need safety features because nobody really knows what battery they have, you just assume it is what it says on the label. But there are a whole lot more Gucci handbags out there than the factory ever made. Lots of people think they have a Gucci handbag but they don't. So, you may think you have two AW cells, but they could be cheap clones with counterfeit labels. And they might not even be Li-Mn cells: they might just be unprotected Li-ion cells.
- APVs need safety features because users make mistakes. Everybody makes mistakes. If your safety depends on never making a mistake, then you are not safe.
- APVs need safety features because the battery condition may be faulty but not have been noticed. Some owners don't even own a meter, so we know this is going to happen in some cases.
- APVs need safety features because batteries can easily be counterfeit. Fake batteries will be the cheapest sort, and most likely rejects. The label may say 'Tenergy' but no one can tell what it actually is.
- APVs need physical safety features because electronic ones might fail. That's what electronics does. And according to the most basic law of engineering, it will fail at the worst time in the worst way and in a chain of failures. People who say it can't happen aren't engineers and should not be building consumer products to be used in front of the face.
- You should think very carefully before buying the cheapest batteries you can get, then stacking them. Especially in a metal tubemod. And especially in one short on safety features.
- Batteries all have a C Rating. Don't use batteries with a C Rating below 2 amps (2,000mA) as they ARE NOT up to the job.
- Bigger batteries are safer because they can handle the heavy load an atomizer puts on them. No big battery (i.e. an 18500 or larger) has ever caused an explosion.
- All batteries can meltdown and cause a fire if faulty and/or abused.
- DON'T put an APV in your pocket or purse with the atomizer connected or the master switch (if fitted) on; or along with keys and change.
- Adapters can be treacherous, so be careful - they can short out.
In the final analysis, mod explosions are caused by corner-cutting and economies of one kind or another. An explosion probably needs a chain of faults, probably including some/all of the following: user error, faulty charger, battery failure, and an APV with no safety features. This chain does happen occasionally, and we now need to take positive action to prevent the situation continuing.
- If the device has several safety features, including the most important of all: a big hole somewhere - then it can't explode.
- If you buy the best batteries you can, and actually receive the genuine article (which you can't guarantee unless you strip them down), and if they are checked regularly, then it is unlikely they will fail.
- If you buy $3 batteries then accept the fact they are less safe than $10 batteries.
- If you buy the cheapest battery charger you can, again, you are adding to the risk.
- Every decision you make, where you cut corners by trying to do it cheaper, multiplies the risk.
- When the APV manufacturer cuts corners, and you then make more economies, the risk is mounting.
Start with a model that has electrical and physical safety features; buy a good battery charger; buy the best batteries you can; and check everything regularly. To minimise risk (most likely to a near zero-risk situation) you would buy a single-battery mod, the best charger you could find, use only AW batteries or similar directly from an authorised distributor, and check everything daily. It's your choice if you don't do that; and you need to be careful if you go the two-battery route.
There is a very powerful trend among APV makers to develop new features, new shiny widgets, and new stylish looks. There is no trend, unfortunately, to develop new safety functionality - and in the end it may only be pressure from ECF that convinces them to incorporate vital safety features.
We believe that there is something fundamentally wrong with this design process - which YOU will pay for unless you personally ARE VERY CAREFUL.
At ECF we have come to the conclusion that all metal tubemods that are designed to accept two batteries, or that could accept two batteries, should have three milled gas vent slots along the body. This is the only single safety feature that will probably always prevent an explosion when other factors combine to create one.
Bottom-end blowout plugs may not work if the failed batteries swell up and block gas venting down the tube - the top end might come off first. Top-end pressure is probably the key issue.
Last edited by rolygate; 09-30-2012 at 06:48 PM.
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