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Name: Brandon
Status: student
Grade: 9-12
Location: IL
Country: USA
Date: November 2008

Question:
Why is hair flammable?



Replies:
Like so much of the human body's soft tissues, the main ingredient in hair is carbon, and carbon is a fine fuel in almost any form other than CO2

Hair is composed of Keratin, a protein made within the hair follicles of your scalp and the rest of your skin. Chemically, keratin is composed of approximately 51% carbon, 21% oxygen, 17% nitrogen, 6% hydrogen, and 5% sulfur. Hair also contains trace amounts of magnesium, arsenic, iron, chromium and other metals and minerals. (Which explains why forensic pathologists can detect poisons or drugs in your hair months later) When enough heat is applied (and it is not a great deal) then the chemical bonds which hold those elements in their place in complex molecules, start to break down, and new, simpler rearrangements are made. The carbon combines with oxygen to produce CO2, The oxygen in the hair gets involved in assisting the burning, the nitrogen gets converted to Nitrogen oxides (and there a number of those) and the sulfur combines with oxygen to produce sulfur dioxide and to a small degree with hydrogen to produce hydrogen sulfide - and it is these sulfur compounds with largely accounts for the smell of burning hair.

Anything is flammable if its component molecules can be persuaded to break down and be rearranged into simpler compounds. We generally think of burning as a reaction which releases heat energy as well, (exothermic) which means that the new compounds have a lower energy level than the ones you start with. For that to be the case, it is best to start with highly complex molecules with lots of branches and multiple bonds in the molecular structure. Any protein would fit that description perfectly. That is why proteins (including meat) are such good sources of energy and why so many animals choose to eat it. Keratin on the other hand is so complex and branched, that it cannot be digested - even owls and reptiles will simply discard the hair of an animal as waste. Given a bit of thermal persuasion though, keratin will break down rapidly, generating enough heat to promote the continuing reaction, and to add to the effect, hair is often covered in natural oils, which promote the burning, and in the case of women, can often be coated with hair spray or lacquer, which may also be flammable.

What do we learn from all this? It is best to put your head to the side to blow out your birthday candles, rather than lean over the top of the cake!

Nigel Skelton
Tennant Creek High School
AUSTRALIA



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