If you’ve spent any time around candles you’ve undoubtedly seen the words flash point on some of the packaging for fragrance oil.  For candle makers, this can seem frightening since the listed temperature can seem really low… and possible in the range you expected to heat it at!  Questions and doubts might run through your mind about using it since it might seem that everything might explode if you add this FO too hot.  Is this real life?  Is a flash point something to be worried about?

What the Heck is Vapor?

If you’ve read how candles really work you might have read the word vapor a few times.  Vapor created from the melted wax is the fuel for a candle flame.  But the word vapor isn’t as easy to understand as solid, liquid or gas.  What is vapor?

Vapor is a state of excitement.  Boiling water is so freaking excited that the molecules on top want to break free and become a gas.  The rest of the molecules want to stay a liquid though, so the top, excited molecules are like, “fine, we’ll be both forms”.  Think of it as a transition – vapor is a strange mixture of liquid and gas.  The important part is that there has to be some excitement for the liquid to want to embrace the freedom of adulthood and become a gas.

And who can blame them?  If it wasn’t exciting to be a gas no one would do it!

Water is just a common example, but the theme remains true for anything that “matters” (see what I did there?).  Liquid + excitement = vapor! And what’s more exciting than fire?  Add a little fire to some liquids and they start vaporizing really easily – things are heating up and molecules are starting to get excited because fire brings energy.  Vapor is just part of the lifecycle of changing a liquid into a gas – it’s no different for fragrance oils.

I want to mention one more thing about vapor before we talk about fragrance oils – there’s typically a little excitement all the time, even without heat or fire.  That’s why a pot of water at room temperature will eventually evaporate over time (it takes a long time since there’s not much excitement). This means there is some vapor-activity going on with the liquid, even if it isn’t being actively heated! 

And what’s almost as exciting as fire?  Zero gravity! Vapors more easily generate when gravity isn’t as strong, such as when you’re in an airplane – water actually boils at a lower temperature in higher altitudes!  This is why certain fragrances can’t be shipped in the air, but let’s talk about that later.

Are Fragrance Oils Dangerous?

The boring background on what a vapor is is really important because fragrance oil vapors are completely flammable.  If you boil a pot of fragrance oil and light a match near the surface once it began rumbling, there would be a flash of brilliant light followed by an instant pang of regret (because you did something stupid).  Don’t do this. 

The vapors are hot and flammable, but they will just harmlessly become an actual gas unless purposefully lit on fire.  It takes a spark of some sort to ignite the fragrance if it’s a vapor.  This is called an ignition source, and it has to be something very hot, like a flame or spark (yes, sparks are very hot).  Only surfaces roughly 750 °F or higher count – a hot fluid (like melted wax at 185 – 200 degrees) is not enough to cause ignition of the vapors.

In candle making this means it is safe to add fragrance oils with low flash points to hot melted wax.  Fragrance oils are a liquid at room temperature (with only tiny bits of vapor, like water in a pot at room temperature too) and aren’t even suspect to ignition.

When the fragrance oil is mixed with the wax we’re now dealing with a “solution” of two different fluids instead of just the fragrance oil on its own.  It has different properties. Paraffin wax, for instance, has a flash point well over 350 °F in liquid form. If you’ve read the chemistry of a candle you might remember that we rely on the flash point to feed the humble little combustion process we’re building into candles.  The mixture has properties that take into account both the wax and fragrance with a flash point somewhere in between them.

If you remember nothing else, a fire will only start at the flash point if there is an actual ignition source like a spark – melted wax will not trigger an ignition.

If you’re cooking up candles in a kitchen with a gas stove, it is absolutely imperative that you follow best safety practices during the process (really you should always be doing this even if you aren’t in a kitchen).  This means having a fire extinguisher nearby. Don’t play around with home-grown solution “fire extinguisher” ingredients like baking soda or salt – do things the right way and buy a dang fire extinguisher.

Why Is It Important?

Remember that little bit about how less gravity equals more excitement?  Candle makers don’t really mind the flash point or gravity-situation, but transportation regulations do.  Vapor more easily comes off in an airplane since it’s more exciting, so carriers will not ship fragrance oils that have a lower flash point in the air.  It’s not because it’s guaranteed to explode or anything, but it limits risk if anything were to happen.

The last thing we want is an incident because a fragrance oil shipment gave off too much vapor.

It doesn’t affect the trade much, if at all.  Some fragrance manufacturers will provide different guidelines on FO temperatures based on the flash point, but science might still be figuring out if that’s a thing.

One final note about safety (again).  Improperly designed candles where the fragrance load is too high will have sweating caused by fragrance “leaking” from the curing wax.  Wax can only hold so much fragrance! If a candle with significant sweat on the top is lit, the flame might heat up the fragrance beyond the flash point and create a dangerous situation. 

The sweating has to be significant for this to matter, but this is why it’s important to follow recommendations from manufacturers about maximum fragrance loads in wax.

Candle Explosions

Everything about flash points applies to burning the candles too. Just because we don’t have to worry about the flash point when we’re mixing fragrance doesn’t mean it’s unimportant.

There are stories all the time about candles exploding in the care of a customer. It’s especially sad when people are hurt and lives are changed forever. Candle makers place a safety sticker on the bottom of their candles but who really reads those anyways?

One of the most important steps in safety is…

Don’t burn candles on or near a hot surface.

…or some variation of that phrase. It’s critical to respect that because hot surfaces can melt more of the candle than the flame by itself which generates extra vapor.

Remember that a candle is a well-balanced combustion machine. Adding more or taking away any of the elements (oxygen, vapor/fuel, or heat) will cause incomplete combustion and potentially grow or kill the tiny explosion occurring at the tip of the wick.

A hot surface that melts more of the candle and creates more vapor potentially introduces a boat load of fuel for the flame to ignite! It goes something like this:

1. Candle is lit and begins to melt it’s wax to draw liquid wax up its wick
2. The liquid wax turns into vapor and is consumed by the flame
3. Candle is happy
4. Candle is happy, but moved to be near something that’s pretty hot, like an oven top
5. The oven top slowly starts to raise the temperature of additional wax in the candle
6. The wax being affected by the oven heat starts to generate a little bit of vapor
7. The small vapor starts to rise and grow
8. The happy candle finds all this extra vapor fuel around it’s flame (no longer confined to the wick area)
9. The flame ignites the vapor – explosion

Explosions are cool, but surprise explosions are not. Remember to preach and practice candle safety.