LPG Gas Blog

Why is a Gas Flame Blue? Blue vs Yellow Gas Flame

Blue gas flames are good. 

Red/Yellow gas flames... not so much...

Gas flames are normally blue but sometimes they burn red or yellow. 

Blue vs Yellow Gas Flame Colour

Blue versus yellow gas flamesA blue gas flame indicates complete combustions, meaning you aren't wasting gas and money.

Red or yellow gas flames may be the sign of incomplete combustion, wasted gas and a serious safety hazard.

With hydrocarbon flames, such as gas, the amount of oxygen supplied with the gas determines the rate of combustion, flame colour and temperature.

Temperature of Blue and Yellow Gas Flames

Yellow and blue gas flame thermometerWith enough oxygen, you get complete combustion and an LPG (Propane) flame burns at a temperature of around 1,980°C.

For Natural Gas (Methane), the temperature is about 1,960°C.

A yellow gas flame is indicative of incomplete combustion and carbon monoxide emissions.

Yellow gas flames only burns at around 1,000 °C.

And Why is it Important?

It does make a difference. 

To understand all of this, we need to look at the background behind flames and combustion. 

The amount of oxygen supplied with the gas is the most important factor in determining the colour of the flame.  

Blue Flame = Complete Combustion

Blue Flame

If you ever took a high school chemistry class and had a chance to use a Bunsen burner, you know how adjusting the air (oxygen) supply affects the colour and temperature of the flame. 

When you adjusted the Bunsen burner to increase the air supply you got more complete combustion, less soot, a higher temperature and a blue flame. 

The gas flame appears blue because complete combustion creates enough energy to excite and ionize the gas molecules in the flame. 

With complete combustion, an LPG (Propane) flame burns at a temperature of around 1,980°C. 

For Natural Gas (Methane), the temperature is about 1,960°C.

Complete Combustion:

Gas + Oxygen = Water + Carbon Dioxide + Heat

Red/Yellow Flame = Incomplete Combustion

Red/Yellow Flame

Again, remembering back to high school, if you starved the Bunsen burner of air, the combustion process was incomplete and the flame burned sooty red or yellow and at a cooler temperature. 

The yellow colour is due to incandescence of very fine soot particles that are produced in the flame. 

This type of flame only burns at around 1,000 °C.

Depending on the lighting, you may have actually seen the soot rising from the flame. 

What you didn't see was that incomplete combustion was also producing dangerous carbon monoxide.

When comparing different gases, you will discover that they required different amounts of air for complete combustion. 

To burn properly LPG (Propane) requires an air-to-gas volume ratio of about 24:1. 

For Butane, it is about 31:1. 

Natural gas (Methane) requires an air-to-gas volume ratio of about 10:1.

Incomplete combustion also results in hazardous carbon monoxide:

Gas + Oxygen = Water + Carbon Dioxide + Carbon Monoxide + Heat

Why is a Blue Flame Safer?

A key warning sign that you require gas appliance servicing is a yellow or red flame or a flame with a yellow burning tip. 

Other indicators include the accumulation of yellow/brown soot around the appliance, pilot lights that frequently blow out or an acrid smell and eye irritation. 

The exceptions to this are gas fireplaces and gas log fires that are designed to have yellow flames.

The above are all indications of incomplete combustion. 

The result is that you could be wasting gas and/or generating dangerous carbon monoxide. 

The latter is a serious safety problem, if it occurs with an indoor appliance. 

If you observe any of these warning signs, you should schedule a service as soon as possible.   

The burner should be cleaned and checked for proper operation. 

Burners blocked with dirt can result in improper combustion, leading to soot build up inside the appliance. 

Carbon Monoxide

Signs of carbon monoxide poisoning
Properly functioning gas appliances are quite safe. 
A blue flame is one indication of proper function and complete combustion.
As discussed, malfunctioning units may generate carbon monoxide, due to incomplete combustion. 
If you experience any signs of carbon monoxide poisoning while operating your indoor gas appliance, you should stop using it until it is serviced by your gas fitter.

How Does a Blue Flame Save You Money?

A blue flame connotes complete combustion. 

This indicates that the gas is being burned efficiently without any unburned and wasted gas. 

With complete combustion you get the maximum heat output from your gas and use less gas to generate heat with whatever appliance you are using. 

You also minimise or eliminate the creation of carbon monoxide.

Final Thoughts

So, now you know why a gas flame burns blue and why it’s a problem if it doesn’t. 

Keep an eye on your gas appliances and have them serviced, as needed, to keep them operating properly and safely. 

Also follow the manufacturers' recommendations for periodic routine servicing.

Your family will be safer and you’ll save money, too.

 

 

 

View More LPG Gas Blogs

Comments, questions or feedback?

Please Email us at: This email address is being protected from spambots. You need JavaScript enabled to view it.

The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.

 

Open new LPG account