Graphite is a substance commonly used in many different household products and you can find it in anything from pencils to tennis rackets. It’s a form of carbon that is relatively cheap to produce and which has some unusual chemical properties, that also make it suitable as a lubricant for certain industrial purposes. But is it flammable and does keeping graphite around the home increase our risk of fires?
Graphite is not considered to be highly flammable, but it can catch fire. It has an ignition temperature of 400 degrees Celsius, (752 Fahrenheit). Graphite is often used for heat shielding even in nuclear reactors because of its ability to withstand high temperatures.
Graphite is relatively common, so let’s take a closer look at this type of carbon to see how it behaves when heated. Here is what you need to know.
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Also read: What Makes Something Flammable?
What Is Graphite?
Graphite is a crystal of pure carbon.
The crystal structure sees the atoms arranged in thin layers of hexagons.
These individual layers are known as “graphene”.
The bonds between each layer are fairly weak and allow the layers to be easily separated or even to slide over each other.
It is the most common naturally occurring form of carbon and if it is subjected to very high pressure and temperature, it will become diamond, the other naturally occurring form of carbon.
Here is a great video all about graphite:
Typical applications of use for graphite include refractories (heat resistant chemical stores), batteries, steel making (mixing graphite with iron changes the properties of steel), brake linings (ever since asbestos was banned), lubricants (the property which allows graphene layers to slip over each other makes it a great lubricant), and pencil “leads”.
Also read: Is Lithium Flammable? Battery Explosions
Is It a Type of Lead?
This leads us neatly to the question as to whether pencil lead is, in fact, lead and, of course, it’s not.
Pencil lead consists only of graphite in relatively different hardnesses and there’s no lead involved in its making at all.
Also read: Is Carbon Flammable? Why it Burns…
Is Graphite Flammable?
Graphite will not burn until it reaches a temperature of around 400 degrees Celsius, or 752 degrees Fahrenheit and it may require greater temperatures depending on the exact formation of graphite that is being used.
This means graphite is not very flammable.
The definition of flammable can vary by source, but anything that has to be heated that much to ignite is not a highly flammable substance.
What Happens When It Is Heated?
Graphite is considered to be “thermally stable” and in many environments, it can be heated to very high temperatures without anything happening to it at all.
However, even if it is not burning, by 700 degrees Celsius (that’s 1292 degrees Fahrenheit) in an oxygen-rich environment, the graphite will start to bond with the oxygen to form carbon dioxide and carbon monoxide.
How Hot Can It Get?
If there is no oxygen present, graphite can withstand temperatures of up to 3000 degrees Celsius and it is used in nuclear reactors and high-temperature furnaces precisely for this property.
Graphite is a very low-cost mineral and this ability to resist very high temperatures can be very useful, indeed.
Will Graphite Ever Burn?
Yes, in the right circumstances graphite will burn and it does so at a minimum temperature of 400 degrees Celsius or 752 degrees Fahrenheit, as long as it is kept in solid form and there is plenty of oxygen available for it to burn with.
However, graphite dust as with many other powders has a much higher surface area to volume ratio than solid graphite and it may ignite much more readily and is, in fact, considered to be an explosive hazard.
If you work with graphite dust, it would be very sensible to ensure that there were no naked flames or potential sources of electrical sparks anywhere around you.
Will It Melt?
Graphite can melt but it takes a temperature of 3,600 degrees Celsius or 6512 degrees Fahrenheit to do so. If you were observing the process waiting for liquid carbon to emerge, you would be very disappointed.
Can It Boil?
Because the boiling temperature of carbon is very close to the melting temperature in both graphite and diamond (there are other forms of carbon where this is not true) and thus graphite boils at a temperature of 3,730 degrees Celsius or 6746 degrees Fahrenheit.
In practical terms, this is so close to the melting point that the carbon does not go through a liquid phase and instead “sublimes” and goes straight from solid to gas.
Did Graphite In The Chernobyl Reactor Burn?
This is a great question and the answer, surprisingly, is no.
While the temperatures in the meltdown of the reactor at Chernobyl would have been extremely high, there was one element missing and without it, the graphite could not burn.
That is oxygen.
While steam trapped in the reactor caused the explosion, the graphite layers on the reactor core never encountered it due to the extreme temperatures and thus, they weren’t able to burn.
Is Graphite Poisonous?
You may have heard at school that graphite was poisonous, but in reality, this is not true.
The reason that many students hear that pencil lead is toxic is because their teachers have mistaken graphite for actual lead.
If you were to eat lead, even in small quantities, you would be poisoned.
However, 1 in 8 atoms in your body (that’s 12% percent) are made of carbon and we are carbon-based lifeforms.
This means that in most cases, graphite is very much non-toxic unless consumed in very unusual ways.
Is It Toxic If Inhaled?
In most cases, inhaling graphite is as harmless as eating it.
Again, as carbon-based life forms, we’re unlikely to be damaged by a little carbon in any form.
However, if you breathe in graphite dust over long periods of time, then you may contract a condition known as “Graphitosis”.
This is a dangerous form of pneumoconiosis which sees the dust build up in your lungs and bronchial tubes and can impede breathing.
There are no known deaths from Graphitosis, but that doesn’t mean that it’s a condition you would want to develop if at all possible.
This means that if you work with graphite dust, it’s important to have breathing equipment and good ventilation to ensure you’re not inhaling too much of it.
Are The Byproducts Of Burning Graphite Poisonous?
When you burn graphite, you get two products: carbon monoxide and carbon dioxide.
Carbon dioxide is also the gas that you exhale when you breathe.
It is not poisonous per se, but if you have a fire and carbon dioxide displaces the air from the room, you cannot breathe carbon dioxide and you will suffocate.
This is, in fact, why smoke inhalation kills more people in fires than the fire does.
Carbon monoxide, on the other hand, is poisonous.
If you breathe too much carbon dioxide, the cure is to start breathing air again.
If you breathe too much carbon monoxide, it is more complicated.
Carbon monoxide binds to the oxygen receptors in your blood, but unlike oxygen it won’t unbind again.
So, when carbon monoxide bonds to a red blood cell, it effectively prevents that cell from ever carrying oxygen around your body again.
This is why they install carbon monoxide detectors in homes, it can save your life.
What Happens If You Smoke Graphite?
It depends on how much graphite you smoke.
We’ve read some colorful accounts of children dying from smoking pencil shavings online, but this is not likely to be due to the graphite in the shavings (and we’re not sure that any of these accounts are valid).
As we’ve already stated, graphite is non-toxic in most circumstances and smoking graphite in the form of pencil shavings is not likely to produce enough carbon dioxide or carbon monoxide to have any significant effect on you.
But please do not try this!
How Much Graphite Is Lethal?
You need 428 micrograms of graphite in every milliliter of blood to die from graphite poisoning.
This is a huge amount of graphite, to the point that you would need to work very, very hard to consume it and in practical terms, in the real world, it’s never going to happen.