It depends mostly on your battery—and, to some extent, how careful you are.

If you see news at all, you hear about people vaping with their electronic cigarettes—and getting blown up by their vapes. But in most cases, it is the battery that has malfunctioned. In fact, over time various cases and investigations have causes the Food and Drug Administration (FDA) to focus on one problem battery in particular: the 18650.

The 18650 battery has malfunctioned a number of times. When it does, it can cause the vape itself to fire into the user’s head, and the battery can catch fire.

The FDA is now moving toward monitoring the 18650 battery, which is a little bigger than a AA battery, but is a lithium-ion version. Vapes that use this battery require you to drop-in the 18650 battery and remove it to charge.

That’s where the trouble comes in. An 18650 lithium-ion battery cell has a stainless steel can, a tough shell that is designed for outdoor use. However, these cells are often used in devices with mechanical mods—and without internal safety circuitry.

This means their insulating wrappers can be damaged as they are repeatedly removed for charging and replaced in their units. Using a damaged cell or drawing too much power can cause metal-on-metal contact and a disaster.

Vapes like JUULs, and others that look like them, do not use the 18650, although they do use other lithium-ion batteries. However, these batteries stay put when charging and the devices do feature overcharge protection.

According to research from George Mason University, more than 2,000 visits to emergency rooms across the US between 2015 and 2017 alone for burns and injuries related to e-cigarette explosions. Most of these were in-pocket explosions—many caused by metal-on-metal contact between keys and vape batteries.

According to a US Fire Administration report from 2017, electronic cigarettes are more likely than some other products powered by lithium-ion batteries to act like “flaming rockets” if there is a battery failure. This is in part because although all lithium-ion batteries contain combustible liquid that can heat and combust, vapes are uniquely likely to be close to our faces or hands.

So, if you’re worried about your vape going off like Apollo 11 in your hand, check the battery. If you can’t remove it, it is not an 18650, and it is in its original condition, you’re probably safe—but you know, maybe put your keys elsewhere.

For a more comprehensive guide on this issue, read our “How to Know if You’re Going to Blow Up While Vaping”