Let's Talk About Fire (Specifically Propane/Oxygen)

Fire has entranced humans from the day we first discovered what it was and how to harness it. But, how many of you know the chemical and molecular reasons fire is, well, fire?

In the jewelry world, we use fire almost every day. Soldering, forging, annealing and metal hardening are all parts of our job. We use propane, oxygen, hydrogen, butane and acetylene for these tasks, but many don't fully understand how the whole fire/heat process works.

I thought it would be fun to break it down to the super fun details. So, here we go! I will use propane and oxygen as my example, however it can be transfered to other gas types as well.
*I am not a chemist. Everything below is from my own learned knowledge and practice/experimentation *
Electrons are negatively charged particles that surround an atoms nucleus. Protons (positively charged particles) and neutrons (neutral particles) exist in the nucleus. Electrons and protons try to maintain somewhat of a balance.

Propane is a hydrocarbon (consisting of hydrogen molecules and carbon molecules). So, in propane we have C³H⁸, meaning there are 3x carbon atoms and 8x hydrogen atoms bonded together via the sharing of electrons in their outer shell.

When there is enough heat present, the oxygen molecules in air (or from a direct source) and propane's hydrocarbon molecules transfer their outer electrons in a chemical reaction to each other, creating stable molecules. These new molecules are either Carbon Monoxide/Carbon Dioxide, water and heat. If it is an 'incomplete' combustion reaction, Carbon Monoxide, water and heat is produced. If it is a 'complete' combustion reaction, Carbon Dioxide, water and heat are produced.

Heat is the result of the speed at which particles move. The faster they move, the more kinetic energy they gain, and the more heat they can produce.

Without an oxygen source (air, bottled, etc) propane cannot go through a chemical reaction and therefore cannot combust/produce heat. If propane was in an oxygen free environment (vacuum chamber, outer space) if it even had a chance to combust, it's by products would not be able to move far enough away from the combustion, and thus would 'smother' or stop any further chemical reaction.

When you see a yellow (soft) propane flame, that is an example of an incomplete combustion. There is a low propane to oxygen ratio. When you see a blue flame, that is a more complete combustion. There is a higher propane to oxygen ratio. One of the reasons an incomplete combustion causes blackening of your metal is because of exess carbon that does not form with oxygen like it would during a complete combustion.
Remember, fire needs 3x things in order to continue being fire: ignition/heat source, fuel and oxygen. If you remove any of those substances, you remove the fire.