E-cigs vs. T-cigs
Electronic cigarettes may be less harmful in the UK than cigarettes but may still be dangerous. Under which circumstances should a person use ecigs? Will they fill your body with plastic?
Electronic cigarettes can contain propylene glycol or vegetable glycerine with nicotine (and in at least two cases polyethylene glycol 400) to form a solution that when heated by an atomizer, produces a visible vapour that provides nicotine to the bloodstream via the lungs when inhaled.
Electronic cigarettes have not been studied enough by scientists in laboratories to form conclusive evidence that their use is either beneficial or harmful to humans. However, some are concerned that unknown side-effects could occur with continuous, consistent use of electronic cigarettes, including cancer.
Behaviour surrounding their use is worrisome because e-cigs are being used habitually by a percentage of non-smokers who otherwise would not use nicotine, they may seem attractive to children, they are not closely regulated, and their use makes it very easy to overdose on nicotine even for experienced smokers.
UK Electronic Cigarettes and E-Liquid
[Thorpe] Welcometo Beyond the Data.
Phoebe Thorpe, and herewith me today is Dr.
Brian King from CDC's Office onSmoking and Health.
Thank you for joining us Brian.
[King] Thanks somuch for having me.
It's a pleasure to be here.
[Thorpe] Our topictoday is E-cigarettes.
Can you tell us why they areconsidered a tobacco product? [King] Yes, so in the UnitedStates we regulate tobacco products through the US Foodand Drug Administration, and the way they describe atobacco product is any product that's made or derivedfrom tobacco.
And we know that the vastmajority of nicotine that's used in tobacco products,including e-cigarettes, is indeed derived from tobacco.
So since these productscontain nicotine, we consider them a tobaccoproduct in the United States.
[Thorpe] And E-cigarettesare little bit different than regular cigarettes.
Can you describe how they work? [King] Yeah, so E-cigarettes isshort for electronic cigarettes, but we know them by alot of different names.
And they can be calledthings like vapor products, hookah pens, vape pens, butthe bottom line is they're all really the same product.
And they work by containinga liquid that's heated which the user then inhales intotheir lungs, and it's important to note that this isn'ttechnically a vapor which is how peoplefrequently refer to.
It's actually an aerosol thatcontains small particles as well as various other ingredientsthat the user inhales, and so there's no combustion.
You're not burning anything, butthere is a heating of the liquid which turns into an aerosolwhich the user inhales.
And they can alsoexhale into the air as other bystandersare around them.
[Thorpe] And the aerosolis not just water vapor.
I mean, that's animportant part to understand because I get asked as aphysician about E-cigarettes, and the thing from the session that I found veryinteresting was the idea that were not reallycertain about the risks that flavorings addto E-cigarettes.
The one that was mentioned wasthe butter flavoring Diacetyl that has been associatedwith bronchiolitis obliterans or what's called popcorn lung,which is a deadly disease.
What more do we know aboutthe risks of E-cigarettes? [King] So our knowledgeabout what's contained in both the E-cigaretteliquid as well as the aerosol hascontinued to evolve over time that these products enteredthe United States marketplace in around 2007.
They didn't really start touptick in use until 2010, 2011.
But, since that time, we reallyincreased the amount of research into what these productscontain.
And what we can say isthat the aerosol admitted by these productsis not harmless.
We do know that the ingredients and the levels aresignificantly less dangerous than conventional cigarettes,but that doesn't mean that they're completelyrisk-free.
And so, some of theingredients we found in the E-cigaretteaerosol are things like ultrafine particulatethat can be inhaled very deep into the lungs, and alsoheavy metals that are found in the filaments of the deviceand are omitted in the aerosol, as well as, things likevolatile organic compounds.
But one of the most commoningredients is nicotine, and we know that nicotineis highly addictive.
But there's alsoevidence indicating that it can harm thedeveloping adolescent brain which really makes itimportant for youth to avoid these devices.
In addition to some of theseother harmful ingredients, we also know the flavorings.
And so, Diacetyl is justone, but there are a variety of different flavoringsthat are used that, although they may be safe toingest in things like food, we don't know what the risks are for inhaling thesedevices into the lungs.
You know, your gut can handlea lot more than your lungs, and that's reallyimportant when we look at the ingredientsin these products.
And finally, it's alsoimportant to remember that people are using a lotof things in E-cigarettes, and that includes otherpsychoactive substances like marijuana andTHC and others.
And so, when we are talkingabout youth in particular, the use of both the nicotinecontaining varieties as well as other varietiesfor other types of drugs are really apublic health concern.
But we have had somerecent good news about the youth meaningmiddle school and high school useof E-cigarettes.
Can you tell me about that? [King] Yes.
It's really a commendablepublic health accomplishment.
We started assessing E-cigaretteuse among youth in this country in 2011, and through 2015,we saw exponential increases in the use of this product.
And 2016 was the first time that we actually saw declineamong youth in this country, and that was really a resultof the coordinated efforts to not only educate thepublic about the harms of youth E-cigarette use but also implementingcommon sense strategies to not only prevent youth accessbut also to protect people from the aerosol andpublic environments and various other campaigns to educate peopleabout these products.
But, on balance, the badnews is that we still have over 2 million youth thatare using E-cigarettes, and they're now the mostcommonly used tobacco products used among US youth.
So we made great progress,but we really need to continue that momentum toreduce all forms of tobacco productuse among youth.
[Thorpe] So it's going down, butnot as lot much as we'd like.
So what's driving the use ofthe E-cigarettes in teens? [King] So there's avariety of factors that we believe are contributingto these increased rates of use among youth thatwe saw through 2015.
One of the most notable is theadvertising for these products.
We know that many of the themesand tactics that have been used to advertise conventionalcigarettes are frequently used for E-cigarettes.
And we also know thatthere's some media of for which conventional cigaretteadvertising is banned that is allowed forE-cigarettes.
Things like television.
And so, there's reallya prominent advertising of these products, and we know that it's reachingkids in particular.
About 18 million US youthreported being exposed to E-cigarette ads in 2014.
Another factor isflavorings, and we know, from the existing science, that flavorings can beparticularly appealing in terms of enticing youth and youngadults to use tobacco products.
And a variety of E-cigarettesare flavored, and we know, from the existing data, thatabout two thirds of youth who use these cigarettes reportusing flavored varieties, and flavors are the mostcommonly cited reason for why youth startedusing these products.
And so, in the end, wereally have a situation where you know the advertisingis bringing the horse to water.
The flavorings aregetting them to drink, and then the nicotine is keepingthem coming back for more.
And so, it's kind of aperfect storm in terms of the youth rates of this use.
But the good news is, we knowwhat works to prevent that.
And if we implement those commonsense public health strategies, we can continue to seethe declines that we saw within the past yearamong our nation's youth.
[Thorpe] And the realconcern is about nicotine and the teenage brain.
Can you just briefly tell mea little bit more about that? [King] Yeah.
So nicotine is found in thevast majority of E-cigarettes that are sold on the U.
marketand, you know, nicotine we use in things like nicotinereplacement therapy among adults.
And it can be, youknow, an effective drug to help people quitconventional cigarette smoking.
But it's important to note thatthose are in very measured doses and weans the individual off of conventional cigarettesover time.
But nicotine is notnecessarily risk-free.
Particularly forvulnerable populations.
We know that nicotineis highly addictive, but there's also a growingbody of scientific evidence that was outlined in a recentSurgeon General's Report noting that nicotine exposure can harmthe developing adolescent brain.
And we know that thebrain continues to develop into young adulthood upthrough 25 or 26, and so, there's really implicationsfor not only youth use of these products butalso young adult use of any nicotine containingproduct.
And another thing to remember with nicotine is it'salso been shown to result in adverse health outcomesamong pregnant women in particularly fetal toxicity.
So there's also implications about pregnant womenusing any form of nicotine containing product,and so, it's really important for them to talk with theirphysician before they use any type of nicotine containingproduct including E-cigarettes.
[Thorpe] So is there a placethat physicians could go to learn a little bitmore about these parts with the E-cigarettesand the nicotine? [King] So there's many resourcesthat have been developed over the past fewyears, particularly as the sciences begun to grow.
And we have, you know,more concrete evidence about what works effectivelyto help warn people about these products and alsoprovide them scientific-based information to makeinformed decisions.
And in 2016, the U.
SurgeonGeneral released a landmark report on E-cigarette useamong youth and young adults.
And as part of therelease of that report, there were severalmaterials including resources and provider cards to helphealth professionals really communicate to both childrenand adults about these products.
And so, in the context of youth, it really enforces theimportance of warning them about the dangersof these products.
Particularly with regardto the nicotine content.
And among adults, it's amore nuanced conversation about knowing that we dohave FDA approved medications to help people quit, and thoseshould really be the first line of defense to help you quit.
And if that doesn't work, youcan consider E-cigarettes, but in consultation withyour healthcare provider.
And right now, based onthe evidence we have, there is no conclusive evidencethat E-cigarettes are effective for long-term cessation, andso, it's really important to use those resources thatwe know are most effective to help you quitand in coordination with your healthcare provider.
[Thorpe] And then foryouth, where if parents or other adults wanted to knowmore about how they could talk to teens and young adults aboutthe risks of E-cigarettes, where would they find someinformation about that? [King] So as part of the releaseof the Surgeon General's Report, there's an excellent interactivewebsite that was coordinated with the release of that report, and it isE-cigarettes.
And it has a varietyof information on both the reportitself as well as a public service announcementas well as informational cards for both parents andclinicians to educate our youth and young adults in particularabout the dangers and risks of using these products.
[Thorpe] That sounds like anexcellent place for our viewers to go and see whatthey can find out.
Thank you very muchfor joining us.
[King] Thank you verymuch for having me.
[Thorpe] And thankyou for joining us.
See you next monthon Beyond the Data.
Construction of electronic cigarettes UK
Disassembled parts of a first generation e-cigarette. A. LED light cover B. battery (also houses circuitry) C. atomizer (heating element) D. cartridge (mouthpiece) Parts of a second generation e-cigarette. An electronic cigarette is a battery-powered vaporizer. The primary parts that make up an e-cigarette are a mouthpiece, a cartridge (tank), a heating element/atomizer, a microprocessor, a battery, and possibly a LED light on the end. An atomizer comprises a small heating element that vaporizes e-liquid and wicking material that draws liquid onto the coil. When the user pushes a button, or (in some variations) activates a pressure sensor by inhaling, the heating element then atomizes the liquid solution The e-liquid reaches a temperature of roughly 100-250 °C within a chamber to create an aerosolized vapor. The user inhales the aerosol, commonly called vapor, rather than cigarette smoke. The aerosol provides a flavor and feel similar to tobacco smoking. There are three main types of e-cigarettes: cigalikes, looking like cigarettes; eGos, bigger than cigalikes with refillable liquid tanks; and mods, assembled from basic parts or by altering existing products. As the e-cigarette industry continues to evolve, new products are quickly developed and brought to market. First generation e-cigarettes tend to look like tobacco cigarettes and so are called "cigalikes". Most cigalikes look like cigarettes but there is some variation in size. Second generation devices are larger overall and look less like tobacco cigarettes. Third generation devices include mechanical mods and variable voltage devices. The fourth generation includes Sub ohm tanks and temperature control devices. The power source is the biggest component of an e-cigarette, which is frequently a rechargeable lithium-ion battery. A later-generation box mod e-cigarette. Image courtesy of Ecigclick An e-cigarette is a handheld battery-powered vaporizer that simulates smoking, but without tobacco combustion. Once the user inhales, the airflow activates the pressure sensor, and then the heating element atomizes the liquid solution. Most devices have a manual push-button switch to turn them on or off. E-cigarettes do not turn on by trying to "light" the device with a flame. The e-liquid reaches a temperature of roughly 100-250 °C within a chamber to create an aerosolized vapor. However, variable voltage devices can raise the temperature. A glycerin-only liquid vaporizes at a higher temperature than a propylene glycol-glycerin liquid. Rather than cigarette smoke, the user inhales an aerosol, commonly but inaccurately called vapor. E-cigarettes do not create vapor between puffs. Vaping is different than tobacco smoking, but there are some similarities with their behavioral habits, including the hand-to-mouth action and a vapor that looks like cigarette smoke. E-cigarettes provide a flavor and feel similar to smoking. A noticeable difference between the traditional cigarette and the e-cigarette is sense of touch. A traditional cigarette is smooth and light but an e-cigarette is rigid, cold and slightly heavier. Since e-cigarettes are more complex than traditional cigarettes, a learning curve is needed to use them correctly. Compared to traditional cigarettes, the general e-cigarette puff time is much longer, and requires a more forceful suction than a regular cigarette. The volume of vapor created by e-cigarette devices in 2012 declined with vaping. Thus, to create the same volume of vapor increasing puff force is needed. Later-generation e-cigarettes with concentrated nicotine liquids may deliver nicotine at levels similar to traditional cigarettes. Many e-cigarette versions include a voltage potentiometer to adjust the volume of vapor created. The amount of vapor produced is controlled by the power from the battery, which has led some users to adjust their devices to increase battery power. An ordinary cigarette compared to a "cigalike" e-cigarette E-cigarettes are usually approximately cylindrical, with many variations: pen-styles, tank-styles etc. Some e-cigarettes look like traditional cigarettes, but others do not. There are three main types of e-cigarettes: cigalikes, looking like cigarettes; eGos, bigger than cigalikes with refillable liquid tanks; and mods, assembled from basic parts or by altering existing products. The primary parts that make up an e-cigarette are a mouthpiece, a cartridge (tank), a heating element/atomizer, a microprocessor, a battery, and possibly a LED light on the end. The only exception to this are mechanical e-cigarettes (mods) which contain no electronics and the circuit is closed by using a mechanical action switch. E-cigarettes are sold in disposable or reusable variants. Disposable e-cigarettes are discarded once the liquid in the cartridge is used up, while rechargeable e-cigarettes may be used indefinitely. A disposable e-cigarette lasts to around 400 puffs. Reusable e-cigarettes are refilled by hand or exchanged for pre-filled cartridges, and general cleaning is required. A wide range of disposable and reusable e-cigarettes exist. Disposable e-cigarettes are offered for a few dollars, and higher-priced reusable e-cigarettes involve an up-front investment for a starter kit. Some e-cigarettes have a LED at the tip to resemble the glow of burning tobacco. The LED may also indicate the battery status. The LED is not generally used in personal vaporizers or mods. First-generation e-cigarettes usually simulated smoking implements, such as cigarettes or cigars, in their use and appearance. Later-generation e-cigarettes often called mods, PVs (personal vaporizer) or APVs (advanced personal vaporizer) have an increased nicotine-dispersal performance, house higher capacity batteries, and come in various shapes such as metal tubes and boxes. They contain silver, steel, metals, ceramics, plastics, fibers, aluminum, rubber and spume, and lithium batteries. A growing subclass of vapers called cloud-chasers configure their atomizers to produce large amounts of vapor by using low-resistance heating coils. This practice is known as cloud-chasing. Many e-cigarettes are made of standardized replaceable parts that are interchangeable between brands. A wide array of component combinations exists. Many e-cigarettes are sold with a USB charger. E-cigarettes that resemble pens or USB memory sticks are also sold for those who may want to use the device unobtrusively. As the e-cigarette industry continues to evolve, new products are quickly developed and brought to market. Various types of e-cigarettes. First-generation e-cigarettes tend to look like tobacco cigarettes and so are called "cigalikes". The three parts of a cigalike e-cigarette initially were a cartridge, an atomizer, and a battery. A cigalike e-cigarette currently contains a cartomizer (cartridge atomizer), which is connected to a battery. Most cigalikes look like cigarettes but there is some variation in size. They may be a single unit comprising a battery, coil and filling saturated with e-juice in a single tube to be used and discarded after the battery or e-liquid is depleted. They may also be a reusable device with a battery and cartridge called a cartomizer. The cartomizer cartridge can be separated from the battery so the battery can be charged and the empty cartomizer replaced when the e-juice runs out. The battery section may contain an electronic airflow sensor triggered by drawing breath through the device. Other models use a power button that must be held during operation. An LED in the power button or on the end of the device may also show when the device is vaporizing. Charging is commonly accomplished with a USB charger that attaches to the battery. Some manufacturers also have a cigarette pack-shaped portable charging case (PCC), which contains a larger battery capable of recharging the individual e-cigarette batteries. Reusable devices can come in a kit that contains a battery, a charger, and at least one cartridge. Varying nicotine concentrations are available and nicotine delivery to the user also varies based on different cartomizers, e-juice mixtures, and power supplied by the battery. These manufacturing differences affect the way e-cigarettes convert the liquid solution to an aerosol, and thus the levels of ingredients, that are delivered to the user and the surrounding air for any given liquid. First-generation e-cigarettes use lower voltages, around 3.7 V. Second-generation PV. Second generation devices tend to be used by people with more experience. They are larger overall and look less like tobacco cigarettes. They usually consist of two sections, basically a tank and a separate battery. Their batteries have higher capacity, and are not removable. Being rechargeable, they use a USB charger that attaches to the battery with a threaded connector. Some batteries have a "passthrough" feature so they can be used even while they are charging. Second-generation e-cigarettes commonly use a tank or a "clearomizer". Clearomizer tanks are meant to be refilled with e-juice, while cartomizers are not. Because they're refillable and the battery is rechargeable, their cost of operation is lower. Hovever, they can also use cartomizers, which are pre-filled only. Some cheaper battery sections use a microphone that detects the turbulence of the air passing through to activate the device when the user inhales. Other batteries like the eGo style can use an integrated circuit, as well as a button for manual activation. The LED shows battery status. The power button can also switch off the battery so it is not activated accidentally. Second generation e-cigarettes may have lower voltages, around 3.7 V. However, adjustable-voltage devices can be set between 3 V and 6 V. Third-generation PV. The third-generation includes mechanical mods and variable voltage devices. Battery sections are commonly called "mods," referencing their past when user modification was common. Mechanical mods do not contain integrated circuits. They are commonly cylindrical or box-shaped, and typical housing materials are wood, aluminium, stainless steel, or brass. A larger "box mod" can hold bigger and sometimes multiple batteries. Mechanical mods and variable devices use larger batteries than those found in previous generations. Common battery sizes used are 18350, 18490, 18500 and 18650. The battery is often removable, so it can be changed when depleted. The battery must be removed and charged externally. Variable devices permit setting wattage, voltage, or both. These often have a USB connector for recharging; some can be used while charging, called a "passthrough" feature. Mechanical mods do not contain integrated circuits. The power section may include additional options such as screen readout, support for a wide range of internal batteries, and compatibility with different types of atomizers. Third-generation devices can have rebuildable atomizers with different wicking materials. These rebuildables use handmade coils that can be installed in the atomizer to increase vapor production. Hardware in this generation is sometimes modified to increase power or flavor. The larger battery sections used also allow larger tanks to be attached that can hold more e-liquid. Recent devices can go up to 8 V, which can heat the e-liquid significantly more than earlier generations. A fourth-generation e-cigarette became available in the U.S. in 2014. Fourth-generation e-cigarettes can be made from stainless steel and pyrex glass, and contain very little plastics. Included in the fourth-generation are Sub ohm tanks and temperature control devices. An e-cigarette atomizer with the coil (heating element) in view. An atomizer comprises a small heating element that vaporizes e-liquid and a wicking material that draws liquid onto the coil. Along with a battery and e-liquid the atomizer is the main component of every personal vaporizer. A small length of resistance wire is coiled around the wicking material and connected to the integrated circuit, or in the case of mechanical devices, the atomizer is connected directly to the battery through either a 510, 808, or ego threaded connector. 510 being the most common. When activated, the resistance wire coil heats up and vaporizes the liquid, which is then inhaled by the user. The electrical resistance of the coil, the voltage output of the device, the airflow of the atomizer and the efficiency of the wick all affect the vapor coming from the atomizer. They also affect the vapor quantity or volume yielded. Atomizer coils made of kanthal usually have resistances that vary from 0.4Ω (ohms) to 2.8Ω. Coils of lower ohms have increased vapor production but could risk fire and dangerous battery failures if the user is not knowledgeable enough about electrical principles and how they relate to battery safety. Wicking materials vary from one atomizer to another. "Rebuildable" or "do it yourself" atomizers can use silica, cotton, rayon, porous ceramic, hemp, bamboo yarn, oxidized stainless steel mesh and even wire rope cables as wicking materials. A 45mm length, extra-long cartomizer. The cartomizer was invented in 2007, integrating the heating coil into the liquid chamber. A "cartomizer" (a portmanteau of cartridge and atomizer.) or "carto" consists of an atomizer surrounded by a liquid-soaked poly-foam that acts as an e-liquid holder. They can have up to 3 coils and each coil will increase vapor production. The cartomizer is usually discarded when the e-liquid starts to taste burnt, which usually happens when the e-cigarette is activated with a dry coil or when the cartomizer gets consistently flooded (gurgling) because of sedimentation of the wick. Most cartomizers are refillable even if not advertised as such. Cartomizers can be used on their own or in conjunction with a tank that allows more e-liquid capacity. The portmanteau word "cartotank" has been coined for this. When used in a tank, the cartomizer is inserted in a plastic, glass or metal tube and holes or slots have to be punched on the sides of the cartomizer so liquid can reach the coil. eGo style e-cigarette with a top-coil clearomizer. Silica fibers are hanging down freely inside of the tank, drawing e-liquid by capillary action to the coil that is located directly under the mouthpiece. The clearomizer was invented in 2009 that originated from the cartomizer design. It contained the wicking material, an e-liquid chamber, and an atomizer coil within a single clear component. This allows the user to monitor the liquid level in the device. Clearomizers or "clearos", are like cartotanks, in that an atomizer is inserted into the tank. There are different wicking systems used inside clearomizers. Some rely on gravity to bring the e-liquid to the wick and coil assembly (bottom coil clearomizers for example) and others rely on capillary action or to some degree the user agitating the e-liquid while handling the clearomizer (top coil clearomizers). The coil and wicks are typically inside a prefabricated assembly or "head" that is replaceable by the user. Clearomizers are made with adjustable air flow control. Tanks can be plastic or borosilicate glass. Some flavors of e-juice have been known to damage plastic clearomizer tanks. Box mod e-cigarette fitted with a rebuildable dripping atomizer (RDA). A view of the RDA deck showing the wicks and coils, juice is dripped into a hopper where the wicks rest as well as atop the coil assembly. A rebuildable atomizer or an RBA is an atomizer that allows the user to assemble or "build" the wick and coil themselves instead of replacing them with off-the-shelf atomizer "heads". They are generally considered advanced devices. They also allow the user to build atomizers at any desired electrical resistance. These atomizers are divided into two main categories; rebuildable tank atomizers (RTAs) and rebuildable dripping atomizers (RDAs). Rebuildable tank atomizers (RTAs) have a tank to hold liquid that is absorbed by the wick. They can hold up to 4ml of e-liquid. The tank can be either plastic, glass, or metal. One form of tank atomizers was the Genesis style atomizers. They can use ceramic wicks, stainless steel mesh or rope for wicking material. The steel wick must be oxidized to prevent arcing of the coil. Another type is the Sub ohm tank. These tanks have rebuildabe or RBA kits. They can also use coilheads of 0.2ohm 0.4hom and 0.5ohm. These coilheads can have stainless steel coils. Rebuildable dripping atomizers (RDAs) are atomizers where the e-juice is dripped directly onto the coil and wick. The common nicotine strength of e-liquids used in RDA's is 3 mg and 6 mg. Liquids used in RDA's tend to have more vegetable glycerin. They typically consist only of an atomizer "building deck", commonly with three posts with holes drilled in them, which can accept one or more coils. The user needs to manually keep the atomizer wet by dripping liquid on the bare wick and coil assembly, hence their name. Kanthal wire is commonly used in both RDA's and RTA's. They can also use nickel wire or titanium wire for temperature control. Variable devices are variable wattage, variable voltage or both. Variable power and/or variable voltage have a electronic chip allowing the user to adjust the power applied to the heating element. The amount of power applied to the coil affects the heat produced, thus changing the vapor output. Greater heat from the coil increases vapor production. Variable power devices monitor the coil's resistance and automatically adjust the voltage to apply the user-specified level of power to the coil. Recent devices can go up to 8 V. They are often rectangular but can also be cylindrical. They usually have a screen to show information such as voltage, power, and resistance of the coil. To adjust the settings, the user presses buttons or rotates a dial to turn the power up or down. Some of these devices include additional settings through their menu system such as: atomizer resistance meter, remaining battery voltage, puff counter, and power-off or lock. The power source is the biggest component of an e-cigarette, which is frequently a rechargeable lithium-ion battery. Smaller devices contain smaller batteries and are easier to carry but typically require more repeated recharging. Some e-cigarettes use a long lasting rechargeable battery, a non-rechargeable battery or a replaceable battery that is either rechargeable or non-rechargeable for power. Some companies offer portable chargeable cases to recharge e-cigarettes. Nickel-cadmium (NiCad), nickel metal-hydride (NiMh), lithium ion (Li-ion), alkaline and lithium polymer (Li-poly), and lithium manganese (LiMn) batteries have been used for the e-cigarettes power source. PV with variable and regulated power offering battery protection. Temperature control devices allow the user to set the temperature. There is a predictable change to the resistance of a coil when it is heated. The resistance changes are different for different types of wires, and must have a high temperature coefficient of resistance. Temperature control is done by detecting that resistance change to estimate the temperature and adjusting the voltage to the coil to match that estimate. Nickel, titanium, NiFe alloys, and certain grades of stainless steel are common materials used for wire in temperature control. The most common wire used, kanthal, cannot be used because it has a stable resistance regardless of the coil temperature. Nickel was the first wire used because of it has the highest coefficient of the common metals. Mechanical PV with a rebuildable atomizer. The temperature can be adjusted in Celsius or Fahrenheit. The DNA40 and SX350J are common control boards used in temperature control devices. Temperature control can stop dry wicks from burning, or e-liquid overheating. Mechanical PVs or mechanical "mods", often called "mechs", are devices without integrated circuits, electronic battery protection, or voltage regulation. They are activated by a switch. They rely on the natural voltage output of the battery and the metal that the mod is made of often is used as part of the circuit itself. The term "mod" was originally used instead of "modification". Users would modify existing hardware to get better performance, and as an alternative to the e-cigarettes that looked like traditional cigarettes. Users would also modify other unrelated items like flashlights as battery compartments to power atomizers. The word mod is often used to describe most personal vaporizers. Mechanical PVs have no power regulation and are unprotected. Because of this ensuring that the battery does not over-discharge and that the resistance of the atomizer requires amperage within the safety limits of the battery is the responsibility of the user.