Lithium Ion batteries are some of the safest and most widely used technologies we have today in portable devices. They are in cell phones, laptops, tablets, MP3 players, radios, GPS devices... you name it... if it's portable, it can be (and probably is) powered by a rechargeable li-ion battery.
There are two basic divisions of Li-Ion batteries--protected and unprotected. The protected batteries have circuitry installed to detect short circuits and prevent the battery from going into thermal armageddon. Unprotected batteries lack that circuitry and depend on the devices they're used in to provide protection. There are further classifications based on the chemistry used in the cells' manufacture.
Generally speaking, eGo and similar self contained units are unprotected cells with safe chemistry, and the battery housing/unit contains the protection circuitry. A quality eGo battery will detect a short circuit in the atomizer, the button will flash three times and the unit will not fire. Variable voltage mods like the Vamo also have protection and also call for safe chemistry unprotected batteries.
Sometimes, due to abuse, misuse or design flaw, that circuitry can fail. However, the safer battery chemistry responds to the problem by venting. Venting is a rapid, heated discharge of gases through the battery housing. Batteries without the safe chemistry are likely to explode. Never, ever use unprotected batteries that do not have the safe chemistry. If in doubt about a particular battery, ask!
Mechanical mods are a different story. Since, by definition they are mechanical and contain no electronics, they require protected batteries regardless of battery chemistry. Use any unprotected battery in a mech mod at your own risk. Regardless of battery chemistry.