Is Sulfur Flammable? Is Burning Sulfur Dangerous? 

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Sulfur is one of the most prominent elements in the universe and is best known by many people for its distinctive rotten eggs smell. This stench occurs in many of sulfur’s compounds, even those found in actual rotting eggs! 

But, should we be concerned when the smell of sulfur hits our nostrils? Is it a sign of a potential fire hazard? 

The short answer is yes, sulfur can be flammable and catch fire easily. This, however, largely depends on the form, with sulfur powder much more likely to ignite than solid sulfur. 

This guide will take a further, more detailed look at the flammability of sulfur including its chemical make-up, the heat produced by burning sulfur, and the various hazards associated with the substance. 

What exactly is sulfur?

Sulfur is a non-metallic element and the tenth most common element in the universe (in terms of mass). On Earth, it rises to being the fifth most abundant element and exists in an unusual molecular structure of S8.

This sees eight sulfur atoms all bonded together in an octagonal shape with bonds moving around the formation. 

Sulfur was once known as “brimstone” meaning “burning stone”, and the element has been used since ancient times in both pure elemental form and mineral form.

In today’s society, it tends to be manufactured on an industrial scale by separating sulfurous contaminants from petroleum and natural gas products.

On the whole, sulfur is mainly used to manufacture sulfuric acid. This is then used in several different types of fertilizer, as well as insecticides and fungicides.

Another use which is falling increasingly out of favor is the manufacture of safety matches and their match heads.

Generally speaking, sulfur is essential for pretty much all known forms of life. Without it, we’d struggle to exist. It appears in three of our amino acids, two vitamins, and several other organic compounds.

What’s more, there are some bacteria located in the earth’s core that don’t use oxygen for their source of energy, but use sulfur instead.

Is sulfur flammable? 

As the name “brimstone” suggests, sulfur is flammable and will very readily catch fire.

Heat can easily break down the octet bonding structure of sulfur, with the element having a low melting point, a low boiling point, and a tendency to sublimate (change from solid to gas without experiencing a liquid stage) when heated rapidly.

When sulfur is burned with oxygen, it subsequently forms sulfur dioxide, a gas that was a significant contributor to the phenomenon known as “acid rain”.

It’s worth noting that sulfur in its normal form (solid) isn’t highly flammable, but will catch fire, with an ignition temperature of 160-190℃ (320-374℉).

This ignition temperature is higher than the defined lowest temperatures for a substance to be labelled “flammable”, but it’s fair to say that sulfur, even in its ordinary form, is readily combustible. 

However, as is the case with all substances, the flashpoint of sulfur is significantly lower when converted into dust or powder.

This is because of the higher ratio of the surface area of the substance to its volume. Sulfur powder is considered highly flammable and must be stored carefully in order for it not to become a serious fire hazard.

How much heat does burning sulfur produce? 

While sulfur reacts readily with oxygen, it’s not a particularly vigorous reaction and produces around 300 MJ/Kg mol of sulfur.

Therefore, in order to increase the temperature of 300 metric tons of water by a single degree Celsius, you’d need to burn 32.07 Kg of sulfur.

To emphasize this further, an Olympic swimming pool contains 2,500 metric tons of water, so to raise the temperature by a degree in the pool, you’d need to burn approximately 250 Kg of sulfur. 

Are sulfur fumes flammable? 

Yes, they are flammable, although given the fact that sulfur becomes a gas at 440℃ and has a flashpoint lower than that, it’s highly unlikely that you’d encounter sulfur fumes that hadn’t already caught fire in such an oxygen-rich environment as the air. 

To produce sulfur fumes that don’t burn and catch fire, you’d need to do so under special laboratory conditions with no oxygen present. 

Is burning the substance dangerous? 

As mentioned earlier, burning sulfur produces sulfur dioxide. Combining this with water makes sulfuric acid – a strong acid that has the potential to damage biological material. 

Unfortunately, as human beings, our bodies are made up of water, and our lungs, airways, and eyes are all sites where sulfur dioxide can quickly become sulfuric acid.

Furthermore, even our skin has moisture on it that could potentially react with the gas. Needless to say, this is extremely dangerous.

Hazards of sulfur 

In its elemental form, sulfur isn’t particularly toxic and exposure isn’t likely to cause you any problems.

However, if you were to consume a significant amount of sulfur it would be sure to upset your stomach and cause distress such as diarrhea.

Breathing in sulfur dust, as opposed to breathing in any other form of dust, can potentially irritate your airways, as well as your eyes and skin. 

Frequently Asked Questions

Does sulfur explode in water? 

No, sulfur doesn’t explode when it’s placed in water. But if you have sulfur with silver bromate and water, this will cause an explosive reaction. Thankfully, the vast majority of us don’t keep silver bromate lying around our homes, workplaces, or offices, so this is a minimal fire risk at best. 

What does sulfur smell like?

Sulfur has a stench of rotting eggs. This is because it’s a sulfur compound in rotting eggs that gives them their smell. It’s worth keeping in mind that lots of sulfur compounds such as hydrogen sulfide also smell of rotting eggs. 

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About David

With over 12 years experience in the fire protection industry, David is our resident Fire Safety expert. He's also a plumber with years of experience in HVAC systems; welding extraordinaire and spends his weekends thinking up gardening projects.

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