Is Acid Flammable? (Hydrochloric)

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If there’s a term that we’re taught to fear during school chemistry lessons, it’s acid. The idea of a substance powerful enough to eat through our skin is terrifying (if not always a wholly accurate representation of things) but is there an extra dimension to that fear? If we work with hydrochloric acid, is it also a fire hazard and if so, what should we do about it? 

Hydrochloric acid is not usually flammable. It tends not to ignite because the acid is dissolved in water, which prevents any fire in most circumstances. However, it can react with other chemicals and potentially cause a fire.

That doesn’t mean that you can be casual about your use of hydrochloric acid, mind you, there are definitely things you need to know about using it safely. 

Your # 1 priority is keeping your family safe. As a firefighter, I recommend everyone has updated smoke detectors that don’t require battery changes, like these ones from Kidde, a fire extinguisher, like this one from Amerex, and a fire escape ladder if you have bedrooms above the first floor, I recommend this one from Hausse.

Also read: What Makes Something Flammable?

What Is Hydrochloric Acid?

Hydrochloric acid, which can also be known as muriatic acid, is hydrogen chloride (HCl) dissolved in water. 

The acid has no color and brings with it a very strong and distinct smell. 

It is one of the stronger acids that we encounter in the laboratory, and we are all exposed to it every day, whether we consciously realize it or not.

That’s because, in common with most animals, the human digestive system uses hydrochloric acid to break down food in the stomach. 

It was almost discovered, by accident, in Persia in the 10th century but, sadly, the chemist carrying out the experiment in which it was produced decided to concentrate on other parts of the output. 

His notes, however, helped the Arab chemists of the 11th or 12th century to work out how to make hydrochloric acid and they detail their methods in De aluminibus et salibus

Those chemists couldn’t isolate hydrochloric acid though and their reactions immediately re-consumed the acid, it wasn’t until the 16th century that European scientists, finally, managed to isolate the acid for use in the lab. 

What Is It Used For? 

As we’ve already mentioned, hydrochloric acid is used widely in nature for its ability to aid in the digestion process. 

When food is consumed, it lands in the stomach which is, essentially, an acid bath and it begins to be broken down into components that can be used by the body. 

It is also used in industrial processes and is produced for pickling steel (that is to remove rust/iron oxide from the iron/steel before it is used in manufacturing), in reactions to produce inorganic compounds, to neutralize alkaline solutions, to boost ion exchangers and for lab use, particularly in titration experiments. 

Is Hydrochloric Acid Flammable?

No, hydrochloric acid is not flammable, nor is it combustible under most normal conditions. 

As we’ve seen, the acid will not burn because of the water content. 

Is It Still A Fire Hazard?

Hydrochloric acid is not considered to be a fire hazard under normal conditions. 

This is because it’s an aqueous solution, that is the hydrogen chloride is dissolved in water.

The water is present in sufficient quantity that any fire is likely to be self-extinguishing and thus, it’s not a fire hazard.

However, it is worth noting that the storage of hydrochloric acid needs to be carried out carefully and the acid cannot be left in close proximity to reagents that react violently in the presence of acid. 

It is possible to cause a fire if such a reaction takes place. 

Hazards of HCL

This shouldn’t lull you into a false sense of security, an acid that is powerful enough to digest the things you eat is powerful enough to come with its own hazards. 

Hydrochloric acid is particularly corrosive and if dropped in the eyes or on the skin or onto mucous membranes it can cause serious damage.

If it is inhaled, it can and will cause irritation of the airways, including inflammation, coughing, hoarseness, and, eventually, pulmonary edema and even death.

Inhaling or drinking hydrochloric acid is also likely to result in poisoning. 

Long-term exposure may cause gastritis, dermatitis, bronchitis, and also, peculiarly, it may make you more photosensitive (sensitive to light). 

Even in very low concentrations, long-term exposure can damage your skin and teeth, leaving them permanently discolored. 

If you work with the acid at concentrations above 0.02 milligrams per cubic meter, this is considered dangerous and leaves you at risk of long-term health conditions.  

What Happens If You Breathe In Hydrochloric Acid?

We strongly recommend that you don’t breathe in hydrochloric acid as this can result in real problems. 

In low concentrations, it can cause tears, coughing, sneezing, and a runny nose. 

In higher concentrations, you will find it hard to breathe, hard to open your eyes and you will start to develop chest pain – it can take 30-60 minutes for these problems to become lethal. 

At concentrations above 1,000 parts per million, death is likely within 30 minutes, and it will feel impossible to breathe.

If the concentration goes above 1,300 ppm to 2,000 ppm, then death is likely to be immediate. 

What Reacts With HCL?

In general terms, hydrochloric acid will react with alkaline metals (and this reaction is violent and potentially a fire hazard), alkaline earth metals (also potentially violent), as well as iron, cadmium, cobalt, nickel, tin, and lead. 

It will also react with most organic compounds including human skin. 

What Shouldn’t You Mix With It?

There is nothing, technically, that you can’t mix with hydrochloric acid but some things are a bad idea to mix with it.

These include cyanide salts (you’ll create hydrogen cyanide gas), sulfide salts (hydrogen sulfide gas), bleach (pure chlorine gas, that’s “mustard gas”), alkali metals (potentially explosive), and hydrogen peroxide (also, potentially explosive). 

Safety Precautions for HCL

Working with hydrochloric acid doesn’t need to be intimidating but you do need to carry out some basic precautions. 

At all times you should be wearing an apron, gloves, and safety glasses that are chemical/acid-resistant.

This will keep the acid away from the skin and most sensitive areas of your body. 

If you’re using a concentrated form of hydrochloric acid, then you ought to be working under a fume hood throughout – inhaling hydrochloric acid is a very bad idea and can cause permanent damage to your lungs and body. 

Here is a video from the Chlorine Institute od HCL safety:

How Do You Clean Up a Spill?

The easiest way to clean up spilled hydrochloric acid is to dust it with sodium bicarbonate (that’s baking soda). 

Then wait until the powdery liquid stops fizzing (or bubbling) and then mop it up with water. 

However, you may also have a “spill kit” if working in the lab and there’s a neutralizing agent in that that you can use instead of sodium bicarbonate.

it’s important to note that this kit is not buffered and you can over-neutralize the hydrochloric acid with it, leaving you with an alkaline solution to clean up – so make sure to follow the kit’s instructions carefully. 

Is Hydrofluoric Acid More Dangerous Than Hydrochloric Acid?

Many people assume that hydrofluoric acid is going to be stronger than hydrochloric acid as fluorine is more reactive than chlorine. 

This isn’t the case because the hydrogen fluorine bond is so strong that it doesn’t ionize very well when dissolved in water.

However, it is more dangerous than hydrochloric acid and is both highly corrosive and highly toxic. 

What Is The Most Dangerous Acid? 

You’re not likely to encounter it, but fluoroantimonic acid is the most powerful acid known to man. 

It is 20 quintillion (that is 20 x 1018) times stronger than sulfuric acid!

It’s so strong that it eats through the glass and can’t be stored in a glass container without it being lined, very carefully, with Teflon first. 

Take a look:

Can Hydrofluoric Acid Dissolve A Human? 

No, in fact, neither will hydrochloric acid. Though both acids will break down some tissues, they would take a long time to do so and the resulting stench would be overwhelming and no matter how long you left your hypothetical body in these acids – it would never break down completely. 

That doesn’t mean you can just play around with these acids, they’re both capable of giving you very nasty burns. 

Can Acid Melt A Diamond?

Acids won’t melt diamonds, but they can damage them. 

There is no acid that is strong enough to completely break down the carbon lattice that forms diamond crystals but some, including hydrofluoric acid and hydrochloric acid, might do some mild damage to the surface of a diamond. 


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