Is hydrogen peroxide Flammable? (A 5-point guide)

This article will answer the following question: “Is hydrogen peroxide Flammable?”. We will discuss rather it can catch fire or not, what are the hazards involved in using it, and other important matters.

Is hydrogen peroxide Flammable?

Precisely, it cannot catch fire. But it can be a fire hazard. Hydrogen peroxide is a strong oxidizer that can enhance a fire, or at least make a source of fuel more willing to ignite. 

Besides, hydrogen peroxide alone can decompose and generate heat, and heat on its own is a potential fire hazard under the right circumstances.

What is Hydrogen Peroxide?

Hydrogen peroxide is a chemical compound that has the formula H2O2. It’s a colorless liquid, more dense and viscous than water. It can decompose readily into water and oxygen, releasing heat.

It’s normally commercialized in a diluted solution, in low concentrations between 3-9%. Even so, it presents a high level of anti-microbial activity.

Hydrogen peroxide is normally used as a bleaching agent and disinfectant. This is thanks to its highly reactive nature. The compound is one of the most common reactive oxygen species.

What is hydrogen peroxide made of?

Hydrogen peroxide solutions are essentially made of H2O2 and water, normally. We will discuss its chemistry in the following topics.

Hydrogen peroxide may seem similar to water (H2O), but that extra hydrogen makes its properties completely different.

What is hydrogen peroxide used for?

Hydrogen peroxide is used as a bleaching and deodorizing agent. It can decolorize hair, wood pulp, fur, and many others.

In chemistry, it’s used as a chemical reactant as a source of peroxides, which are a precursor of chemical synthesis.

Here’s a list of other important applications:

  • Paper industry;
  • Cellulose industry;
  • Food industry;
  • Wine industry;
  • Plasticizers;
  • Rocket Fuels;
  • Foam making;
  • Glycerol manufacturing;
  • Dyeing;
  • Antiseptic;
  • Hydroxylation;
  • Cleaning metals.

Is hydrogen peroxide dangerous?

Hydrogen peroxide is a strong oxidizer, it’s capable of detonation or strong decomposition, it can cause serious temporary or residual injuries, and it’s corrosive and irritant.

Hydrogen peroxide hazards

The following 3 pictograms show the most relevant hydrogen peroxide hazards.

Although it’s not flammable on its own, it can still cause a fire or explosion. 

The compound is a strong oxidizer that can interact with fuels, making them more willing to suffer combustions. Also, Hydrogen peroxide can decompose itself and generate heat, which enhances the flammability of other compounds on its own.

The peroxide is also a corrosive material and can cause severe skin burns and eye damage when in high concentrations. 

It presents acute toxicity to humans, from both oral intake and inhaling it.

NFPA 704

Many government and non-governmental organizations establish systems, codes, and categories to express the overall hazards substances have.

The NFPA 704 is a standard maintained by the National Fire Protection Association, based in the U.S.

Also known as Safe Square and Fire Diamond, it uses a diamond with four divisions and colors. Each is rated on a scale of 0 to 4, known as Degrees of Hazard.

The four divisions have one color each. The red on top indicates flammability, the blue on the left indicates the level of health hazard, and the yellow on the right is for chemical reactivity. The white at the bottom contains codes for special hazards. 

The specific hazards classification of Hydrogen Peroxide can be displayed as the following:

The specific number can vary according to how concentrated the hydrogen peroxide is. This diagram was made for a specific hydrogen peroxide solution of 50%.

Hydrogen peroxide chemistry

Hydrogen peroxide is a molecule made only of hydrogen and oxygen. But unlike water, it is not a stable compound. 

As you can see from the image below, the compound can decompose itself. The chemical bondings between the oxygens get undone and broken in half. 

The result is a reactive oxygen species called peroxyl (OH⋅).


Such species are known for their high reactivity. They can imply oxidative stress in cells, damaging proteins and membrane lipids. This is the same mechanism that kills pathogens.

Note that there are two paths a hydrogen peroxide molecule can take to decompose: generating those peroxyl radicals or generating water and oxygen. Both are dangerous when it comes to fire.

Although hydrogen peroxide, peroxyl radicals, oxygen, and water cannot burn, this chemical decomposition can generate heat that can be enough to facilitate a fire or make it grow bigger.

Besides, the peroxyl radicals can react with fuel molecules and break them, weakening their connections and facilitating combustion to happen.

Physical and chemical properties

Here’s a list of other physical and chemical properties:

  • Chemical formula: H2O2
  • Molar mass: 34.0147 g/mol
  • Appearance: Very light blue liquid
  • Odor: slightly sharp
  • Density: 1.11 g/cm3 (20 °C, 30% (w/w) solution)
    1.450 g/cm3: (20 °C, pure)
  • Melting point: −0.43 °C (31.23 °F)
  • Boiling point: 150.2 °C (302.4 °F) 
  • Solubility in water: Miscible
  • Solubility: soluble in ether, alcohol
    insoluble in petroleum ether
  • Acidity (pKa): 11.75
  • Viscosity: 1.245 cP (20 °C)
  • Heat capacity (C): 1.267 J/(g·K) (gas)

2.619 J/(g·K) (liquid)

  • Decomposition enthalpy: − 23.44 kJ/mol
  • Std enthalpy of formation (ΔfH 298K): −187.80 kJ/mol

Can hydrogen peroxide even burn?

As we saw in the last chapters, hydrogen peroxide presents no flammability. It cannot burn because the combustion reaction won’t happen to it. But it doesn’t mean it’s not related to fire.

This may sound weird, but hydrogen peroxide does have a considerable fire hazard associated with it. This is because the compound can decompose itself, thanks to its instability.

This decomposition is an exothermic reaction, a kind of chemical reaction that liberates energy. This energy comes in the form of heat, something it has in common with combustion.

So, combustion doesn’t happen but it produces fire anyway? Not exactly. Not all forms of heat are kinds of fire, but all fires are hot.

Fire only appears when something organic is burning, like wood, gasoline, wax, or natural gas. It happens due to the oxidation of organic matter (made essentially by carbons and hydrogens).

If hydrogen peroxide is decomposed, only heat would appear.

But an important problem of hydrogen peroxide is its capability of enhancing the flammability of combustible substances. 

Because it generates reactive substances, the “peroxides” we spoke about in the chemistry chapter, can interact with the sources of fuel (organic matter), oxidizing it.

The oxidation of organic matter is a problem if there’s also a possibility of fire to happen. The fuel is weakened, can catch fire more easily and, if there’s already a fire, it can grow even bigger.

Therefore, hydrogen peroxide is not flammable but is certainly a fire hazard, under the right circumstances.

Hydrogen peroxide Safety Data Sheets

You can check more specific relevant information regarding the safety of the product in material’s safety data sheets, documents made specifically for this end.

The more concentrated they are, the more hazardous they’re as well.

What are the commercial percentages of hydrogen peroxide?

The major commercial hydrogen peroxide percentages commercially available are the following: 20, 27, 30, 35, 50, 60, 70, and 90%.

A few stabilizers can be added to help avoid decomposition, in a weakly acidic solution, mostly made of organophosphorus compounds.

Hydrogen peroxide is mainly manufactured by a process called anthraquinone, an industrial process. It basically uses hydrogen and oxygen gas in the presence of a catalyst to form H2O2.

Is hydrogen peroxide explosive?

Hydrogen peroxide can become explosive if in high concentrations, and/ or heated. 

The chemical decomposition of hydrogen peroxide is an exothermal reaction, meaning that it liberates energy. If many particles of the peroxide are allowed to decompose at once, it can happen harshly.

Hydrogen peroxide, even if diluted, can become explosive if heated. The compound has a low flashpoint and can decompose even before reaching a vapor state.


Hydrogen peroxide is not flammable in the sense that it cannot catch fire or serve as fuel, but it can enhance and facilitate a fire to happen because it’s a strong oxidizer.

Oxidizing agents normally interact well with organic compounds, and all our sources of fuel are organic, thus why the risk is so imminent. Besides, the peroxide can decompose and generate heat on its own, without any other reactant.

Frequently Asked Questions (FAQS): Is hydrogen peroxide Flammable?

is hydrogen peroxide safe?

The Food and Drug Administration (FDA) classifies hydrogen peroxide as safe for humans, but only at low doses. But it also alerts that is possible that hydrogen peroxide may cause irritations and skin burns, even if used once in a while.

is hydrogen peroxide an acid?

Hydrogen peroxide has a pKa of 11.75. On this scale, water is 14. This means that hydrogen peroxide can be considered a weak acid.

Hydrogen peroxide can serve both as an oxidizer or a reductant, depending on which solution it’s applied to. If it’s left in an acidic solution, it will act as an oxidizer, even stronger than chlorine.

is hydrogen peroxide safe for ears?

Hydrogen peroxide is commonly used in ear drops, to treat ear infections and remove earwax. These specific solutions are prepared for this end, so they are safe.

But is not advised to use any kind of hydrogen peroxide in your ear. Always read the label first to make sure.


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