Is Alcohol Flammable? (A Comprehensive Overview)

Is Alcohol flammable?

Ethanol, also called alcohol or ethyl alcohol, is flammable. In both states, liquid and gaseous (vapor), ethanol is flammable. It can also be flammable when mixed with other substances.

Ethanol can often be in different conditions of pressure and temperature, as it is often mixed with other substances, such as water and hydrocarbons. When in hydrocarbon solutions, it remains flammable.

Ethanol also remains flammable when mixed with water (in drinks for example). Ethanol also evaporates relatively easily.

Where is Ethanol Used in Everyday Life?

Ethanol is present in many products of common consumption in industry and in personal uses. It can be present in drinks, in the fuel (of cars, and aircraft), among many others.

  • Drinks.
  • Antiseptic materials for its ability to eliminate microbes.
  • Pharmaceutical mixtures.
  • Cosmetics.
  • Perfumes.
  • Automobile fuel (alone or mixed with gasoline).
  • Rocket fuel.
  • As a solvent for many organic materials such as oils, fats and hydrocarbons.
  • In industrial organic synthesis, ethanol can be a solvent, reagent or both.

Some Properties of Ethanol

Ethanol, at ambient conditions, is a colorless liquid with a characteristic and somewhat pleasing smell. Its chemical formula is C2H6O, its chemical structure can be represented as C3CH2OH. 

Since it has an hydroxyl functional group (OH), which performs hydrogen bonds, ethanol is highly polar. Hydrogen bonds are also the main reason ethanol is miscible with water.

Below some properties of ethanol are listed.

  • Colorless liquid.
  • Completely soluble in water.
  • Soluble in many organic compounds including hydrocarbons (e.g. gasoline).
  • Boiling point: 78 °C at 1 atm.
  • Freezing point:  -114 °C at 1 atm.
  • Flash point:  10 – 13 °C at 1 atm.
  • Autoignition temperature: 365 °C at 1 atm.
  • Ethanol is denser than gasoline and less dense than water.
  • If mixed in water ethanol is completely miscible, it is possible to distillate it from water but to obtain water free ethanol more sophisticated methods are necessary.
  • Ethanol can dissolve electrolytes, therefore it can conduct electricity.
  • Ethanol vapor is denser than air.

Some Facts about the Flammability of Ethanol

The lower flammability limit of pure ethanol is 3.3% (in volume) in atmospheric air, temperature and pressure. While the upper flammability limit of ethanol is 19.0% (in volume) under the same conditions of atmosphere, pressure and temperature.

Ethanol is hardly ever only ethanol, even if pure ethanol is obtained, it quickly starts absorbing water from the air.

In many cases, ethanol is in a mixture with water. In stores ethanol is often found as a solution with water, in drinks ethanol can be present from percentages ranging from under 5% to higher than 40%.

Ignition sources (heat, sparks, flames)

Heat can be from flames, something hot or chemical reactions that produce heat.

Flame visibility of ethanol

Pure ethanol flame is easily spotted, but it is not as bright as a typical gasoline flame.

Ethanol Fires Recommendations

Water jets are dangerous in ethanol fires, as it can spread the fire.

Fire extinguishers marked B, C, BC or ABC are the appropriate ones to be used.

As for foams, class B Alcohol-Resistant (AR) foams should be used. since ethanol can dissolve AFFF-AR or fluorine based foams. 

Flash Point of Ethanol

The flashpoint of a given liquid, is the temperature (at 1 atm) in which the liquid’s vapor is in a minimum concentration to produce fire if in contact with air and a flame.

The flash point for ethanol is around 10 °C, this temperature value may vary depending on how pure the ethanol is as well as the atmospheric pressure.

Studies have been made to investigate the flash point of solutions of water with ethanol. Below some values are represented.

Relative mass fraction of ethanol water (%)Flash point (°C)
543
1031
2025
5020
7016
10012

Auto Ignition Temperature of Ethanol

Auto ignition temperature is the temperature in which a given substance will spontaneously ignite in ambient air and pressure.

In the case of ethanol, that temperature is 365 °C. However, under higher atmospheric pressure, the auto ignition temperature is lower. 

What fumes are produced from burning ethanol?

The combustion reaction of ethanol with the air will produce carbon dioxide and water. Ethanol flame under standard pressure and temperature is around 2100 °C.

As is the case with any fire that uses the air as the oxidizer, ethanol fire consumes the oxygen in the air, posing danger of suffocation.

Can ethanol chemically react with something to cause fire?

If in contact with alkaline metals, ethanol mixtures can generate a lot of heat. When in contact with metallic sodium (Na0) ethanol reacts quickly generating a high amount of heat and also releasing hydrogen gas (H2). Hydrogen gas can also pose a danger of fire.

Are Alcohol Drinks Flammable?

Yes, even drinks containing 1% alcohol can be flammable, since the flash point of a water solution with 1% ethanol is around 80 °C.

Drinks that contain higher amounts of alcohol pose a higher risk of fires. Such drinks include vodka, whiskey, rum and tequila.

If left open for enough time drinks will gradually lose their alcohol content by evaporations of ethanol.

What is E85 and is it Flammable?

A blend of gasoline with ethanol with 85% ethanol is called E85. That allowed amount of ethanol can be under 85% depending on the local regulations. It is highly flammable regardless of the ratio of ethanol/gasoline.

What are Other Commonly Used Alcohols Besides Ethanol?

Chemically speaking, an alcohol is any organic substance that has an hydroxyl group (OH) chemically bound to a carbon atom which is bound to only hydrogen or other carbon atoms.

Methanol (CH3OH) is also highly flammable and highly hazardous.

Isopropyl alcohol (C3H7OH) is also flammable. Some rubbing alcohols contain isopropyl alcohol.

As a side note, cholesterol itself is an alcohol, although its physiological and physical properties are very different.

In terms of its chemical reactivity it can be similar to ethanol. As both ethanol and cholesterol have a slightly acidic hydrogen atom (from the hydroxyl group).

Methanol Hazards

Methanol (also known as methanoic alcohol, methyl alcohol or CH3OH) is also highly flammable. It has a slightly lower boiling point than ethanol and hence it is easier for methanol to generate vapors. 

Methanol vapors can travel far distances and still be capable of catching on fire. Methanol originated fires are recommended to be extinguished using water spray (do not use water jets as it can spread the fire), carbon dioxide, dry chemical or ethanol-resistant foam.

Methanol is considerably more toxic than ethanol if ingested or if inhaled. Possibly causing blindness or even death.

Isopropyl Alcohol Hazards

Isopropyl alcohol (also known as isopropyl alcohol, isopropanol, C3H8O or (CH3)2CHOH) is commonly used as the antiseptic agent in rubbing alcohol.

It is highly flammable, it has a boiling point of 82 °C, higher than ethanol, and therefore it is harder for it to produce vapors than it is for ethanol. Its flash point is 11 °C. And its low and high flammability are 2 and 13% respectively.

Isopropyl alcohol poses a higher danger than ethanol if ingested (oral LD50 5045 mg/Kg for rats).

Conclusion

In this article, some aspects of ethanol and its flammability were addressed. Some proper safety precautions were explained.

Some aspects regarding hazards of isopropyl alcohol and methanol were exposed.

To summarize, fire and alcohol are not a safe combination given the immediate fire danger they pose.

Frequently Asked Questions (FAQ): Is Alcohol Flammable?

Is alcohol rubbing flammable?

Alcohol rubbing is composed of water and either isopropyl alcohol or ethanol. Both these alcohols are flammable.

Is alcohol dangerous if ingested?

If alcohol is ingested it can cause difficulty in breathing, mental confusion, difficulty maintaining consciousness, slow heart rate, stomach problems, clammy skin, dulled responses such as no gag reflex (which prevents choking), hypothermia, brain damage.

Ethanol has a lethal oral dose (LD50) of 7340 mg/Kg in rats.

Is biodiesel flammable?

Yes, biodiesel is highly flammable. Biodiesel consists of ethanol that was obtained from plant sugar rather than from petroleum derivatives. In fact fuels must be flammable in order for the to be suitable for generating energy.

Is 70% alcohol flammable?

Yes, the alcohol in 70% alcohol is isopropyl alcohol, which is highly flammable. The 70 alcohol name may also refer to ethanol solutions with 70% ethanol, and these solutions are also flammable.

What plants have ethanol?

Ethanol is usually extracted from biomass by means of fermentation of the sugar in plants. The most commonly used plants for ethanol production are corn, sugar cane, sugar beets among others.

Is it safe to light rubbing alcohol on fire?

Rubbing alcohol is flammable, lightning it up can cause fires and small explosions. If under heat rubbing alcohol quickly releases vapors that can affect the central nervous system if inhaled.

Can alcohol catch on fire without air?

Without air it can still catch on fire as long as there is an oxidizer in sufficient contact with the alcohol. In the case of an alcohol, such as rubbing alcohol, catching on fire the alcohol is the combustible (or fuel) and the oxygen in the air is the oxidizer.

Do humans produce ethanol naturally?

Yes, humans do produce ethanol with the help of microbes in the digestive system. Most of the ethanol that is ingested or synthesized within our bodies is degraded in the liver by the alcohol dehydrogenase (ADH).

Can methanol poisoning be cured by ethanol?

Yes, ethanol is the standard treatment for methanol poisoning.

References

Ethanol safety data sheet found in the sigma-aldrich website.

Christian J.R. Coronado, João A. Carvalho, José C. Andrade, Ely V. Cortez, Felipe S. Carvalho, José C. Santos, Andrés Z. Mendiburu, Flammability limits: A review with emphasis on ethanol for aeronautical applications and description of the experimental procedure, Journal of Hazardous Materials, Volumes 241–242, 2012, Pages 32-54. https://doi.org/10.1016/j.jhazmat.2012.09.035

Log, T.; Moi, A.L. Ethanol and Methanol Burn Risks in the Home Environment. Int. J. Environ. Res. Public Health 2018, 15, 2379. https://doi.org/10.3390/ijerph15112379

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