This post contains historical information from mid-2010, some of which is out of date. It will NOT be edited to reflect current information.
For the latest information and advice please see:
Incidents involving mods
Updated October 2010
There have been numerous documented reports with photographs of explosions and fires caused by 'mods' (custom-built or modified e-cigarettes). It is now time for us all to take steps to improve the safety of mods and if possible to reduce the danger factors inherent in these devices. ECF has long warned about the various safety aspects involved - sometimes in the face of strong resistance - but now even modders who previously denied this was an issue have admitted they were wrong.
The main factors causing the risk are:
- Use of cheap, unprotected rechargeable Li-ion batteries
- Such batteries combined in series
- Use of batteries that are far too small for a high-current device such as an atomizer (the smallest cell where all types on sale will handle the current safely is an 18500)
- some kind of fault in the battery itself (since it is usually too small to handle the current draw safely, in the case of a fault condition there is no safety margin and it blows, taking the other battery with it)
- Not checking the final charge voltage of the battery charger
Additional risk factors:
- Overvoltage being applied to atomizers that are designed to work at a maximum voltage, which HV mods exceed, thus pulling more amps from a cell that cannot handle the current draw
- Dead short (short-circuit) occurring in a single battery mod
- No gas vent holes, or an insufficient number of holes, or a bottom-end blowout plug, that would allow a faulty unprotected battery to degas with relative safety
- Lack of a kill switch (a second 'transport' switch that allows the battery pack to be disconnected for travel and storage)
- The use of a cheap and under-specified switch for the main on/off switch
- The owner mistakenly charging standard, non-rechargeable batteries
An intrinsically unsafe mod, combined with unsafe batteries, is a risk that should be avoided. Component failures or operator error are inevitable and must be planned for.
What appears to happen during an explosive incident is that a high-voltage mod, operating at 5 volts or higher, experiences an electrical fire; a large volume of inflammable gas that cannot be vented quickly enough is released from a battery experiencing a short-circuit; and an explosion results. Or, the gas is ignited by the electrical fire and an explosion or fire results. The gas vented from these cells is hydrogen.
There are no incidents yet reported of 3.6 (standard voltage) mods exploding - there have been reports of meltdowns, though - but this does not mean such an incident is impossible, perhaps just less likely. In addition, purse and pocket fires probably occur due to lack of a kill switch, and overall system voltage does not appear to be a factor in these incidents. Such fires might lead to more serious incidents such as home fires or traffic collisions. Therefore all high-capacity rechargeable battery custom-built e-cigarettes are implicated.
The electrical incident that causes subsequent battery failure is now known to be, usually, high charge state (and possibly an over-charge situation) combined with first operation after recharge pulling too much current for the battery size and C-rating, causing thermal runaway followed by violent de-gassing or explosion. This typically involves an unprotected Li-ion battery - other types such as Li-Mn are not implicated as their technology is much safer. Note that a user has reported an incident where standard non-rechargeable batteries (Li-ions in this case but probably any type is dangerous in this situation) were charged by mistake and then exploded violently when used in a mod (with no gas vents).
CR123-size rechargeables of different types - both Li-ion and cheap Li-FePo4 cells - seem to be involved. It can be noted that CR123s are among the smallest, and are therefore most likely to be over-stressed by use on an atomizer, which since it is likely to draw 1.5 to 2 amps is way over the recommended discharge current (C-rating) for these cells, which is just 500mA (half an amp). Atomizer failure or a switch failures may be implicated, but the most common failure mode for unprotected Li-ions seems to be freshly-charged batteries on first or second operation. This may mean that the charger is faulty, or simply that the batteries could not protect themselves from overcharging. A fault of some kind probably needs to exist in the battery. For example some lithium batteries are extremely sensitive to impact damage, Li-Po cells being the most delicate (they are known to explode after being dropped).
Ordinary Li-ion batteries (non-rechargeable or 'primary' cells) have also exploded after being mistakenly charged then placed in a mod, and these batteries are more dangerous as there are no built-in gas vents (rechargeable batteries have small gas vents built in, you can often see the tiny holes next to the top button).
A main on/off switch that is rated at sufficient amperage for the load is needed, but sometimes cheap under-rated switches have been used. The main reason for this is actually that small, high-load switches are not easily sourced, not that mod builders try to cut corners, since mods are often built as extra-quality items where dollar savings are not a primary concern.
Another problem is that all current atomizers are low-voltage but many mods run on high-voltage. These terms are relative since we are talking about 3.6 volts at the lower end (the nominal voltage that an atomizer is designed to run at), and 6 volts (the nominal voltage a two-battery mod may be designed to run at).
However it is worth considering that a nominal voltage is just that - a rough figure. For example, with car and boat batteries, the nominal system voltage is 12 volts but the alternator charge voltage is actually 13.2 volts, and an alternator with a management controller, or a full-feature marine alternator (the use of either of which is the only way to ensure a fully-charged battery) will charge for short periods at 14.4 volts. The system therefore needs to be able to withstand voltage peaks of around 15 volts or more.
Although the nominal voltage of a two-battery mod where the batteries are wired in series is 6 volts, it is possible that the peak system voltage with newly charged batteries may be 8.4 volts (2 x 4.2 volts). This is more likely to lead to incidents since the atomizer design voltage is clearly being exceeded. An atomizer probably needs to work (ie heat up a wire in a similar way to a glowing filament in a light bulb, in order to heat a liquid and convert it into steam) at as low as 3.1 volts, since this might be the system voltage in a standard e-cigarette with a partly-discharged battery. Applying nearly three times this voltage to one is not inherently safe as more power is drawn and this may lead to over-stressing the battery, especially when it is of small format (bigger batteries are safer).
January 2012 Update
The most serious mod explosion so far has just taken place. It involved Li-FePo4 cells, and there is a possibility that the cheaper type with an insufficient C rating were used - though we do not know at this time. DO NOT use Li-FePo4 cells with a C rating less than 4C. Real, proper Li-FePo4 cells have a 5C rating or higher (some are 10C).
What happens when batteries fail
A fault condition occurs in which an unprotected and possibly faulty battery is overcharged, then subject to a high drain (normal atomizer use) causing it to fail, and the battery casing melts due to the heat generated. As the casing fails, large quantities of hot, flammable gas are released. If the e-cigarette body is unvented, the device explodes, since in most respects it resembles a bomb, which is simply a sealed metal casing inside which large quantities of gas are generated rapidly. The critical factors are the volume of gas, the speed of gas creation, the flammability of the gas, and the cross-sectional vent area or lack of it (how many and how big the vents are). Note that battery thermal runaways normally produce hydrogen gas. One battery failing may take out the other one, if there are a pair.
If the casing is vented but poorly, the device if unrestrained will act as a jet engine, expelling burnt gas through a vent and accelerating away. If restrained (as in a pocket or in a purse / handbag), the device will act as a small flamethrower, expelling a quantity of hot or burning gas. If in the hand and in use, as has happened and been documented, then injury is likely.
Note that incidents of all these types have occurred.
The legal liability for selling products that may be subject to such issues is of a serious nature and cannot be avoided. Mods have caused injuries and unless mod builders take this issue seriously, that will continue. It is not possible to avoid liability if the product is known to be dangerous and has previously caused injury.
Update July 2010
We had considered various courses of action: forming an approvals committee and/or the banning of mods with no safety features from ECF.
Warnings to buyers were issued and advice to modders was given.
However, it now looks as though many commercial modders have looked at the situation seriously and introduced safety features, therefore progress is being made. It seems that mods are now more likely to be built with safety features.
In the future, all forms of ecigarette will probably need a UL or CE mark as this is the basic consumer protection. It seems reasonable that mods should be built now to a specification that would succeed in achieving a pass in the certification procedure for these marks.
Moves are proceeding in several countries to form trade bodies, mainly in the face of threats from uncontrolled regulatory authorities. Such trade bodies would probably consider this issue at some stage.
What ECF has done
- Buyers are warned about the obvious and proven dangers, though perhaps we should make such warnings more numerous and more obvious.
- We advise people not to use unprotected batteries under any circumstances.
- We advise mod builders to incorporate safety features.
- Our own mod safety specification is available.
What we should do better
- We should publish lists of safe batteries.
- We must continue to keep this issue in front of industry members.
An outline for an ECF Mod Safety Specification. This comprises a minimum specification and does not address switch ratings (as they are almost impossible to verify), defined battery make and model (as this is a user-purchased consumable), or charger make and model (as this requires further investigation). The specification will not be used to approve or reject mods advertised on ECF, it is offered in order that there is some form of standard - or even just a basis for debate. We welcome others to use it or contribute to its improvement.
Protected batteries, if supplied
'Safe technology' batteries are preferred: Li-Mn.
Li-FePo4 can be used but they MUST HAVE a C rating of 4C or over. Cheap Li-FePo4 cells must not be used.
Li-ion batteries, if used, should have dual protection: both overcharge and dead short (short-circuit) protection.
Gas vent holes
Holes must be drilled to vent the gas that might result from heavy charging or a short-circuit.
A minimum of two holes are required, each of which must be of 2mm diameter or larger.
Radially-drilled holes are preferred to holes in the end of the casing, since if they are in the end then the mod will be propelled strongly in the opposite direction, perhaps toward the face. Radial holes (holes around the outside, probably at the lower end), are preferable as they will not impart any thrust during a gas vent incident.
A kill switch
A second switch that disconnects the batteries totally during transport and storage.
There are some factors associated with the main on/off switch that could be considered:
- A switch that is rated for the current flow. Some switches are just too small and will burn out. There is a slight risk they may lock on. Small switches rated at 3 amps plus are admittedly not easy to find. DC current is far more damaging to switches (and everything else - including humans, in high-voltage shock situations) than AC and therefore a switch that carries any appreciable DC current has to be over-rated for the job.
- A sealed switch. Occasionally a switch has operated by itself when liquid leaked onto it, so that sealing it in some way appears to be a good idea, if it is vulnerable to liquid leaks.
Gas blow-out plug
Metal tube mods are intrinsically very strong. This is a problem when they contain potentially explosive materials, as you are then looking at the definition of a grenade. In January 2012,
the most serious mod explosion yet has just taken place. The metal tube mod involved was reported to have no gas vents or other safety features. The top blew off into the user's face, causing serious injuries, and the victim was in the ER on breathing assistance.
We are clearly talking about potential for serious injuries here. It has been suggested that a press-fit or other type of plug at the lower end is a good idea, as this will blow out first. The top end blowing off first has been shown to be dangerous.
A note on batteries
Incidents are caused by a combination of operator error and a mod with no safety features. The most likely operator error is the use of the wrong type of batteries. Since it is inevitable that occasionally a user will be supplied with the wrong batteries, it is essential that mods have safety features.
It is up to the supplier whether they want to include batteries but if they do, the batteries need to be of a known safe type. Safe batteries should not self-destruct even when used in an unsafe mod.
Note that batteries can be described as 'protected' but not be. Also, they can be described as 'protected' but have only 50% of the required safety features, as both overcharging and short-circuit protection are required. They need to have a comprehensive built-in electronics package that stops them being overcharged, and that stops them delivering a high current when shorted out.
Some batteries may be mis-labelled or otherwise faulty when they appear to be of the correct type and in good condition. Therefore:
MODS MUST HAVE SAFETY FEATURES OR THEY ARE DANGEROUS.
ECF strongly advises you not to buy or use an unsafe mod. A mod of merchantable quality is one that is designed to use protected or safe-technology batteries, has gas vent holes, and a kill switch. If it has all these, and a UL or CE mark, then it might be described as safe since it has the required safety features and a consumer approval testing certificate.
There is a school of thought that says no such devices are truly safe, but that is a matter for the buyer's decision.