The heater coil in an atomizer or cartomizer, or any of the equivalents, is a liquid-cooled nebulizer system that depends on a proportion of submergence and a proportion of liquid-saturated surrounding gas to maintain its temperature below a critical level. The liquid refill can be vaporized at around 70C, but if the liquid runs out then the temperature can climb to over 300C.
The transitional stage is immediately obvious to any experienced ecig user because the vapor essentially disappears and is replaced by hot dry air, followed by smoke. The problem is perhaps that new users will not expect this; or not know of this; or not have been given instructions in their starter kit that specifically warned about this issue.
Many atomizer systems will survive a 'dry burn' of this type, but most cartomizer systems won't. If the atomizer has a silica wick that can survive high temperatures, and is of a high build quality and with no adhesives/sealants adjacent to the coil, it may survive without problems, although its service life will probably be reduced. This is inevitable if the coil is regularly taken a long way above 70C. Cartos generally have polyester wadding or similar materials near the coil, which are immediately burnt by high-temperature events, and the taste is permanently degraded from that point.
The fumes/smoke produced when the refill liquid runs low or runs out are preceded by a 'dry hit' (no vapor), and followed by progressively more fumes.
The process is: the nichrome or kanthal coil temperature rises to ~300C; any nearby heat-sensitive materials such as adhesives, sealants or coatings, will start to melt; if the atomizer wick or bridge wick are made from low quality materials (instead of high-temp silica rope), they will begin to be burnt; then the temperature of the main structure of the atomizer starts to rise.
The steel tubular structure, the nichrome coil, or the ceramic cup the
coils sits in are not likely to be able to create fumes in significant quantity before the other more vulnerable materials present produce unpleasant fumes in such quantity that it should not be possible in practice to inhale the output of the device.
You can see this effect in clinical studies where the researchers didn't know that the devices are gravity-fed liquid-cooled systems, and tested them upside down and also beyond the 'puff limit' of the refill cartridge, resulting in the anomalous presence of a variety of toxic contaminants produced as a result of melting plastics and so on. No user would be able to inhale such materials, it would be the equivalent of being in a burning building.
I don't personally feel that metal fumes are an issue here, more the plastics and other materials present.
It also seems a good idea to me that vendors should include a guide to use that mentions the fact that a dry hit immediately precedes damage and there may be potentially toxic products on the next vape. There does seem to be too much dependence on good luck with these products instead of clear guidance.
Then again, there is probably an element of the 'expert's blindness' in it, too: because an expert knows everything about a product, they cannot conceive of the issues faced by someone totally ignorant of the product whilst also isolated from all advice. This is why usability testing always includes a number of people who have never even seen the type of product before and are deliberately not told how to use it, either. It always throws up some amazing errors that no expert could possibly foresee, as the actions needed to produce such problems appear, to them, to be blind stupidity; whereas all that is taking place is the normal activity path of someone who doesn't have a clue what the product is or how to use it.
All we need to do to find such instances of 'blind stupidity' is to look at clinical research on, and lab tests of, e-cigarettes. It doesn't seem conceivable that people could be stupid enough to make the errors they regularly do, and which are then even published as research. All that is taking place here, though, is that you can expect a series of mistakes by the naive (used in the medical
sense here, meaning the uninformed in these particular matters) if you don't give them precise instructions. For example:
- Don't use it upside down, it's a gravity-fed device.
- Your carto has about 5 or 6 'cigarette equivalents' in it (and with about 24 - 30 puffs for each 'session' as opposed to the 12 puffs in a cigarette, as there is far less nicotine in ecig vapor than is present in cigarette smoke). Trying to get more than that out of one will result in problems.
- If you get a dry hit then it's done. Refill it or throw it. The next drag won't be nice at all...
- Suck very gently and very slowly compared to a tobacco cigarette.
- Anything less than 4 seconds, with a small device, won't produce any usable result.
- Use the mouth only, not the lungs, by 'sucking' and not 'inhaling'.
- Hold the vapor in the mouth for a second or two, then inhale the vapor if you wish to. Then exhale through the nose - slowly.
This is probably the minimum in terms of instructions that should be supplied with any ecig, as these advisory points stop the most often-seen errors.
