The search does not seem to be working, and as this is an important question, we should give you an answer. The answer isn't simple but it's worth considering the implications.
Experience has taught us that while cheap two-battery HV vaping looked a great idea two or three years ago, it has risks. This is one of the reasons VV vaping (at HV) with electronic controls is popular - risk reduction. It is absolutely true that thousands of people have used 2-cell HV devices with no problems at all, but unfortunately about a dozen have had explosive battery failures that caused the device to fragment. In a couple of cases there were serious injuries reported. In fact the first ever civil suit brought by a user who is claiming substantial damages for injury is now taking place, and it involves the make you are talking about. Until the case is resolved, of course, no real statement can be made about it.
Everyone has different opinions about this: some say that since they have been using these devices with two cells for X years, they are happy to continue; others say they will never use a two-cell mechanical or electrical (as against full electronic control) device again. It's entirely up to the individual.
The incidents have involved the following devices, and
only these: metal tube APVs, with two cells inserted, of the mechanical or basic electrical type, with no electronics.
If you are going to continue using such a device for two-cell HV vaping, you might take the latest knowledge into account:
1. Only use safer-chemistry cells such as Li-Mn or Li-FePo4.
2. Since battery counterfeiting is now widespread, be aware that in reality you have absolutely no idea what batteries you are actually using. Because of this, #1 is moot.
3. All safety features fail - and sometimes in a chain. This is the only way to explain the fact that a dozen or so of these devices have exploded when in theory it is either 'not possible' or 'extremely unlikely'. Some devices have very little in the way of safety features, though.
4. There is only one design feature that will save your bacon when all else fails: very substantial gas vents. Without extensive (and expensive) testing it is impossible to say how big these need to be, but an estimate is 600 mm2, which equals for example 3 x 4mm slots x 50mm long (3 x 2" slots of 5/32nds width).
5. The gas vents need to be especially capable
at the top end of the battery tube, as it appears that this is where pressure builds up, causing the top of the device to fragment.
ECF battery and APV resources
http://www.e-cigarette-forum.com/fo...9007-warning-rechargeable-batteries-apvs.html
http://www.e-cigarette-forum.com/forum/ecf-library/129569-rechargeable-batteries.html
http://www.e-cigarette-forum.com/forum/announcements-news/274600-safe-metal-tube-apvs.html
http://www.e-cigarette-forum.com/fo...-ecf-metal-tubemods-safety-specification.html
EMSS
The ECF safety specification is currently on hold because a new independent standards body, the IECSB, is being formed to take on this role. It met for the first time this week, so progress is being made.
