Re: What is the blue area underneath the yellow flame of a fire?

The blue area is the part of the flame where combustion is the most 
complete.  Here very little else is produced aside from heat and light 
when compared to the yellow part. Of course carbon (C) is produced as well 
as small amounts of carbon dixoide (CO-2) and carbon monoxide (CO) as well 
as other molecules interacting with the atmosphere but not in the 
abundance these same gasses and elements are being produced in the yellow 
part of the flame. The blue part of the flame is where the fire is most 
efficient, like a fuel efficient automobile, if you will. In the yellow 
area, carbon, carbon dioxide and carbon monoxide are being produced in 
very large amounts as compared to the blue area. The next time you have an 
opportunity to watch a gas powered stove top, observe it on low and notice 
how little yellow there is. Now turn the stove up and notice how much more 
yellow there is. (Please make sure an adult is present!) This is due to 
the same thing that was going on with your candle - inefficient use of 
fuel and therefore high production of fire gases such as carbon dioxide, 
carbon monoxide and water vapor as well. Recently, here in Kansas City we 
had the City's worse ice storm in history and 285,000 people were left 
without electricity, some for periods of a week or more.  Many older 
people were using their gas stoves to help them keep warm as their 
furnaces would not work without the electricity the thermostat uses to 
send a signal to the furnace that the house needs heat.  Due to the fact 
the homes were closed up and they were burning there stove tops to keep 
warm, many were overcome by carbon monoxide poisoning. This was due to the 
fact they were burning their stoves much too long in a poorly ventilated 
area. As the oxygen in the homes' atmospheres began to be used up, the 
stoves created more and more carbon monoxide (CO) and a snowball effect 
was produced.  Two people lost their lives and many others required 
hospital treatment. Imagine the amount of yellow in some of those flames!!
Carbon monoxide is a colorless, odorless gas which asphyxiates its victims 
by attaching itself to the hemoblobin in the blood 250 times more readily 
than does oxygen (O-2). Its symptoms are flu like with dizziness, nausea 
and splitting headaches being reported. Eventually it will kill if a 
person does not get out of the effected area and to a medical treatment 
facility. Sometimes brain damage can be sustained by those who are 
resuscitated too late in the poisoning process.

you can access more information about fire at you local library in basic 
chemistry and physics books. Most of my information came from the 
Internation Fire Service Training Associations' book "Essentials of 
Firefighting" 4th ed.

Thanks for the question. Keep up the curiosity about things scientific.