Is Iodine Flammable? (A Comprehensive Overview)

This article will answer the following question: “Is Iodine Flammable?”. We will discuss if iodine is flammable if it can catch fire, and which are the fire hazards involved.

Is Iodine Flammable?

No, iodine is not flammable. In its pure and solid form, Iodine can’t catch fire. No flames would appear in an attempt of burning it. Although, in temperatures above 184°C/363.9ºF it can become airborne, and highly corrosive vapors can appear.

What is iodine?

Iodine is a chemical element.

It is the fourth halogen, a member of group 17 in the periodic table. It’s the heaviest member of its group, and also the heaviest essential mineral nutrient for our bodies.

It exists in many forms. We usually don’t encounter it in its pure form, only in salts or in a liquid solution. Commercially available forms of iodine are not pure forms of it.

Iodine is solid and has the formula I2 in its pure crystalline form, but it can also be a gas and present the same formula. It also exists as Iodide (I), iodate (IO3), some kinds of acid, and periodate anions (IO4, IO6−5, and others).

Iodine’s primary use is in our nutrition. We require Iodine in our bodies so it can synthesize thyroid hormones. The lack of it may lead us to disinvolve goiter disease and prejudice the central nervous system development in fetuses and infants.

Knowing that iodine deficiency is prejudicial, some governments oblige manufacturers to supplement table salt with iodine. Around 88% of all households worldwide use iodized salt, but it’s still a problem in some underdeveloped countries.

Some forms of salts considered gourmets, such as Himalayan Pink Salt, Kosher salt, Smoked salts, and others, may not have iodide added to their formulation.

If you mainly consume a salt that doesn’t contain iodine, consider speaking to a doctor about starting iodine supplementation.

Industrially, iodide anion is used as a catalyst in the production of acetic acid, and in organic chemistry to synthesize certain polymers.

Iodine chemistry

Iodine is a big chemical element. 

It has 53 protons in its nucleus. The biggest a nucleus is, the higher the number of isotopes a chemical element has.


There are 37 iodine isotopes known by mankind, but only one of them is stable, the “127I”. This number is the weight each atom has. This is the one iodine atom we can find in iodophor solutions, supplements, and any other commercially available form.

Other iodine isotopes are radioactive, have a short life and suddenly are torn apart to produce lighter compounds such as Antimony and Tellurion.

The “131I” isotope is commonly produced in fission nuclear plants, it’s created inadvertently in nuclear reactors by the decay of “132Te”.

The half-life of this Tellurium compound is around 3 days, which may not look much, but it’s more than enough to cause serious problems in accidental environmental contaminations. But our body can’t distinguish between Iodine atoms. 

Our thyroid will consume the radioactive atom unwillingly, which can cause many problems. To prevent that, Iodine supplements are given to populations close to radioactive contaminations, to reduce the uptake of radioactive iodine.

Iodine properties

  • State: solid
  • Melting point: (I2) 386.85 K ​(113.7 °C, ​236.66 °F)
  • Boiling point: (I2) 457.4 K ​(184.3 °C, ​363.7 °F)
  • Density: 4.933 g/cm3
  • Triple point: 386.65 K, ​12.1 kPa
  • Critical point: 819 K, 11.7 MPa
  • Heat of fusion: (I2) 15.52 kJ/mol
  • Heat of vaporisation: (I2) 41.57 kJ/mol
  • Molar heat capacity: (I2) 54.44 J/(mol·K)
  • Natural occurrence: primordial
  • Crystal structure: ​face-centered or orthorhombic
  • Thermal conductivity: 0.449 W/(m⋅K)
  • Electrical resistivity: 1.3×107 Ω⋅m (at 0 °C)
  • Magnetic ordering: diamagnetic
  • Molar magnetic susceptibility: −88.7×10−6 cm3/mol (298 K)
  • CAS Number: 7553-56-2
  • Oxidation states: −1, +1, +3, +4, +5, +6, and +7


I2 in its elemental form is barely soluble in water.

To dissolve one gram in water is required 3450ml (116.6 fl oz) of pure water, at 50ºC. Although, the compound is more soluble in organic solvents such as hexane and tetrachloride.


Among the halogens, iodine is the atom with the lowest first ionization energy. This means that in group 17, iodine is the compound that requires the least amount of energy applied to lose one electron and become an ion.

This also explains why the compound has the lowest electronegativity, lowest electron affinity, and lowest reactivity in the group. Imagine that an atom is like a magnet. The stronger it is, the better it will attract magnetic metals and alloys. 

Note that this relation is in comparison with other halogens fluoride, chlorine, and bromine. The iodide anion is still a very reactive species, which is why it’s a strong oxidizer used in sanitization.

Is iodine flammable? Is it a fire hazard?

No. Any pure form of iodine is not flammable.

Part of the reason that makes a fuel catch fire is the combustion reaction. When something reacts with oxygen, and this reaction liberates energy from beneath the fuel chemical bondings, the fire appears as a rea combination of heat and light.

This same reaction can also have another name: oxidation.

Although it’s not like any other oxidation, it’s a reaction that happens in a gas state. Even if the fuel is liquid, it gotta become airborne so the reaction can happen.

But iodine is already an oxidation agent, it already acts chemically similar to oxygen. This means that a reaction between iodine and the air’s oxygen wouldn’t happen normally and that no energy would be generated by it.

Summarizing: iodine can’t catch fire because the chemical reaction that generates the flames can’t happen. Iodine and oxygen gas can’t react with each other under normal circumstances.

But remember when we told that combustion was only one part of fires? We will discuss more in the topic below.

Iodine can still become airborne by reaching a vapor form if it’s heated. It doesn’t generate flames but unleashes toxic vapors.

Why iodine is used as an oxidizing agent?

An oxidant is a compound that can accept electrons from a donor.

Species like oxygen and iodine tend to receive electrons, that’s why they form anions instead of cations.

Oxidizing agents are species that can receive electrons really hard because they have high reactivity.

These compounds often have good antimicrobial properties. This happens because microorganisms can suffer oxidation. Life forms are all carbon-based and are made from organic matter.

Likewise, fuel sources are made of organic matter, and can suffer combustion (oxidation). This means that fire, oxidation, fuels and oxidizing agents have a really close relation.

The Fire

Fire is something intrinsically related to life.

Nevertheless, fire only happens on our planet, as far as we know.

All organic matter on our planet originated from life at some point. Inorganic compounds normally can’t burn.

Fire is something that started on our planet only after the plants settled on the land, which occurred more or less 400 million years ago. There was heat back then, but no fuel to burn.

There are three ways in which the thermal decomposition of organic matter happens: oxidation, pyrolysis, and evaporation/ vaporization.

All three happen at once during a fire. How fire will look depends on how these three events happen. 

For example, in a blue fire from an oven, oxidation is almost the only thing that happens, because the fuel is already vaporized (it is a gas), and its chemical composition is simple (the carbon chains are small), so pyrolysis can’t be seen.

In a fireplace, although, we can see many more yellow and red flames, smoke, fumes, and all kinds of byproducts from incomplete combustion. This happens because the chemical reactions are much more complex since the fuel has a very different composition.

When wood burns, the solid material is constantly being stimulated to a vapor-like state and suffers all kinds of breakdowns before finally reacting with oxygen (combustion). All these chemical reactions lead to many byproducts, many of which are toxic to us.

Iodine, although, doesn’t suffer a reaction with oxygen like that. But similarly to fuels, iodine can assume a vapor state of matter, become airborne and cause harm to our health.

What happens if iodine is tossed into a fire?

We spoke a lot about how fire is an oxidation, and how organic matter suffers oxidation. We also said that iodine can become an oxidizing agent. What if we combine this all?

Well, if a fire is installed (which means, a combustion reaction started and won’t cease easily) and an oxidation agent is applied to the fire, the flames can grow even bigger.

This happens because any kind of oxidation is also a decomposition reaction. The oxidizing agent can make the fuel molecules “weaker” because it helps break down the molecules.

The result of tossing iodine into a fire is a bigger fire.

Iodine Safety Data Sheets (SDS)

There are many SDS for iodine online. The documents present important and reliable safety information about products.

As expected, all the following iodine products are considered not flammable, but strong oxidizers that can be hazardous to our health.

You can check some in the following links:

  • Iodine’s Hazardous Substance Fact Sheet, according to the New Jersey Department of Health;
  • Iodine for laboratory use, from LabChem;
  • Iodine by, Inc.


Iodine is not flammable, it can’t burn, and no flames would appear from an attempt of burning it. If heated enough, iodine can unleash toxic vapors in the air. If tossed into a fire, since it’s a strong oxidizer, iodine can enhance the combustion of other substances.

Frequently Asked Questions (FAQS): Is Iodine Flammable?

Is iodine a metal?

No. Iodine is a nonmetal from the halogen group, in the periodic table. All atoms from this group are not metals.

Is iodine diatomic?

Yes. Pure iodine occurs in a diatomic form. Its formula is I2.

Is iodine polar?

Iodine is non-polar. It has a diatomic structure, where both iodine atoms share equally the electrons. Also, there’s no difference in electronegativity because the molecule is made from two equal atoms.


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