Is Styrofoam Flammable? [Polystyrene]

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There was a time, not so long ago, that every fast-food meal came in a Styrofoam container. You don’t see them as often now because well, it’s an environmental hazard and it’s possibly not good for your health either. That doesn’t mean, however, that the use of Styrofoam has been completely eliminated and one question many people have about Styrofoam is, is it a fire hazard?

Styrofoam is flammable at higher temperatures and can catch fire. It will melt at 212 degrees Fahrenheit, ignite with a spark at 680 degrees Fahrenheit and auto-ignite at 800 degrees Fahrenheit.

Styrofoam can certainly be a fire hazard in the right conditions. Let’s find out more, shall we?

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Also read: What Makes Something Flammable?

What Is Styrofoam?

is styrofoam (polystyrene) flammable?

Styrofoam is a trademark. It is used to refer to a particular form of extruded polystyrene foam (XPS), which is known as “Blue Board” and it’s owned by the Dow Chemical Company.

And this article is not about that Styrofoam.

That’s because the word Styrofoam is used colloquially throughout North America (and much of the rest of the world to mean polystyrene foam (EPS) and it is from this that our coffee cups and fast-food containers are made. 

It’s also used for insulation and for packing materials too. In fact, it’s very likely that you’ve received a parcel at some point full of small polystyrene chips that would also be called (incorrectly, of course) Styrofoam (packing peanuts). 

To date, because it is incredibly cheap to produce polystyrene in all its forms, including both uses of Styrofoam, has been one of the most commonly used plastics in the world. Unfortunately, this is bad news for the environment as it is universally regarded as non-biodegradable and it can take thousands of years to decompose in landfills. 

And even worse, animals don’t recognize polystyrene as something artificial and because it is often used to hold food or drinks – they can mistake it for actual food. Sadly, this isn’t without consequences for the animals involved and they can become very sick from eating large quantities of the plastic as it is mildly toxic. 

Styrofoam is now banned in many places around the world for use in food and beverage containers, but it persists in many others, for now. 

At What Temperature Does It Catch On Fire?

Styrofoam (polystyrene) will easily catch fire if you expose it to a naked flame or spark around 680 degrees Fahrenheit (360 Celsius). 

It will auto-ignite around 800 degrees Fahrenheit (427 Celsius).

They do make different flame retardant versions of polystyrene (EPS), take a look at the difference:

Burn Test: Regular vs Flame retardant EPS (styrofoam)

Burn Or Melt?

Styrofoam can both burn and melt, however, it’s worth noting that it is much more likely to melt than to burn. 

You’ll find that around 212-238 degrees Fahrenheit (100 – 120 Celsius) that it starts to noticeably deform and then at around 320 degrees it will melt. 

This means that it’s safe to use in a microwave (as long as you’re not microwaving it for hours) because it won’t get hot enough to melt in the microwave, and even if it does, it won’t catch on fire because the microwave has no means of getting that hot.

But it also means you need to be careful putting this kind of container in the oven or under the grill.

If you don’t pay close attention to the temperature – the plastic will melt, and molten plastic is not going to be very good for your oven or any other appliance.

And… the fumes are toxic. They contain a substance known as styrene (this is how poly-styrene gets its name – it is lots of styrene molecules joined together). 

Styrene gas is known to be very harmful to the nervous system and can cause long-term problems. 

What Happens When You Burn Styrofoam?

When Styrofoam burns it does so with sooty and slightly oily smoke. This is probably indicative of the fact that it’s not fully combustible and you’re getting a bunch of different (and not fully understood) byproducts from the flames.

There’s more bad news when it comes to Styrofoam – when it burns, the gas that it releases is considered to be highly toxic when inhaled.

It seems likely that this smoke contains both styrene and other forms of toxins that you’d prefer not to inhale. 

Does this mean that Styrofoam is a fire hazard?

Well, sadly there’s no official definition of “fire hazard”, but we’d suggest that you don’t keep it in any place where it’s likely to be exposed to a naked flame and ignite. And that you keep it away from any other heat sources, such as; grills, ovens, water heaters, and even garbage disposal units. 

It’s best not to take any chances with a product that might release dangerous gas into your home.

What Temperature Can It Withstand?

polystyrene cups

Styrofoam won’t auto-ignite until it reaches temperatures of around 800 degrees and that means it can be used as an effective insulator as long as it never comes into contact with a flame.

So, if you want to use it to keep the heat in or out of somewhere, you can, but it must have an effective flame barrier in front of it or it may burn. 

Is It Heat Resistant?

Yes, though Styrofoam will eventually deform and then melt, it’s reasonably heat resistant.

That’s why they put hot coffee and hot food in it- it stays warm and insulated inside, but won’t burn your fingers on the outside (in theory, at least – always be cautious when picking up a hot coffee or meal, even in Styrofoam packaging). 

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