Are CDs Flammable?

In this article, we will unveil the following question: “Are CDs Flammable?”, and other important questions about Compact Discs, how they work, and why. 

Are CDs Flammable?

No. CDs are not a fire hazard. But they can still heat a lot, melt and unleash toxic gases.

What Are CDs?

A Compact Disc is a digital optical disc data storage format.

CDs have 4 layers. A thin and light polycarbonate plastic layer where the data is stored, a shiny layer that allows the reflection of laser beams, a lacquer coating that protects the shiny part, and a top layer that allows the printing of the artwork.

A CD is encoded with tiny cavities that will, later on, receive a laser beam from reading devices. This will be reflected on the shiny layer (normally made of aluminum) and returned to the equipment, then be computed and presented on a screen.

An audio CD player has a motor that spins the disc between 200 and 500 rotations per minute (RPM). Since the CD starts being played from the inside of the disc to the outside edge, in the beginning, it spins much faster than in the end.

This happens because the data transmission rate must be the same in any part of the disc. But the inside is much smaller than the edge, hence the need for a bigger velocity.

The data is retrieved in a spiral. This is possible because the laser is placed on a mobile mechanism that starts slowly walking along the rail, covering the CD entire surface.

How do CDs work?

Even though CDs are getting obsolete, their functioning is not simple. We will do our best on explaining how it works, as simple as it gets.

CDs are encrypted with digital information, but this is done physically.

The discs have pits embedded in them, small gaps carved into one of their layers. 

The pits are analogous to the grooves on LPs, but instead of requiring a stylus to walk mechanically through its cavities to create an analog signal, CDs are read by a laser beam.

The data surface is embedded inside the CDs, to protect it from abrasive dust and variations in temperature. A protective plastic layer is attached on it to this end.

CDs pits and LP grooves.

Source: https://www.dak.com/vinyl-record-grooves-magnified-1000x/ and

LPs have a contiguous route to follow. CDs also have a path to follow, but this is done by the laser beam.

CDs are not touched to be read, so they never wear out. But of course, since they spin rapidly and are handled in and out of reading devices, they will eventually get damaged.

When a CD is burned (recorded, not set on fire), the data starts being recorded from the inside, and a path is slowly carved until the border. So a device reads CDs from the inside as well. 

CD starts spinning, and the light used to read it starts moving slowly towards the end.

What the laser bean do is shed light on the encrypted surface. This light then reflects, change its properties, and then is read by the equipment. We will comment more about it soon.

The language in which the information is encoded in CDs is similar to binary language (a computer language) and braille.

But how information on CDs is read?

The biggest difference between analog and digital signals is that the second one is much more complex and robust. CDs use digital signals.

LPs grooves require a physical device to help read the information directly. This very own reading can damage the vinyl, so a copy made of an LP would never be the same as the original. Also, the copying process would keep adding more mistakes to it.

In CDs, this doesn’t happen. The laser beans practically can’t harm the CDs.

As you can see from the previous picture, CDs, DVDs, and even Blu-ray discs are pretty much the same thing, but the technology required to put more data on discs is very different.

The amount of data capable of being recorded is bound to the size of a CD. Think about the CD pits and lands as letters. What do you do to write more on a small piece of paper?

Yes, you write smaller letters. Likewise, Blu-rays require smaller carvings. At the same time, the laser must be capable of reading it, so a bean of smaller sizes must be used.

The kind of data embedded in CDs is binary and is read as numbers by the reader device. This is the real difference between analog and digital devices.

When the laser retrieves information from a cd, the signals it passes to the equipment are encoded numbers. What the device does is adjust and transform these numbers in a way a screen can understand.

Every time a CD spins the laser is focusing on a single point. When it encounters a pit, it obliges the light to be reflected in a different manner. But the beam does not fit entirely inside the pit, some light still reaches the surface.

The outcome from these different reflections is that the beams interact with each other and get canceled (lasers are nothing more than light, electromagnetic waves that can be altered like the waves in a lake).

The result is an absence of light signal in the CD reader. The lands (the surface not carved), in contrast, represent the whole original laser bean since they don’t suffer that destructive interference.

From this pattern of light and absence of light, a complex binary language rises, a pattern that is read and transformed in the CD reader device.

CDs properties and chemistry

Information is printed on the CDs physically. This is a form of encoding that consists in creating patterns on the CDs. The CD readers will shed laser beams later on and retrieve the data.

This printing is done by making microscopic pits in one layer of the disc. These are nothing more than really small dots, little cavities on plastic that play the most important role in the confection of the discs.

The plastic used in CDs is polycarbonate.

It is obtained in a chemical synthesis that uses Bisphenol A (BPA) and phosgene (COCl2), along with many other compounds. There are other routes but this is normally the most used.

Polycarbonate is a kind of polymer. These structures have complex chemistry and synthesis. 

They are formed using basic units called monomers, who are forced to bond with each other, creating a very long chain.

Source: adapted from https://www.canstockphoto.com.br/structure-feito-pl%C3%A1stico-phosgene-a-17261417.html and https://pslc.ws/macrog/pc.htm

The red dots are oxygens (O), the grey ones are carbons (C) and the small white balls are hydrogens (H). The ring structures are named phenols and are very important in organic chemistry.

Each monomer bonds with each other, it occurs next to the red dots. The resulting molecule is very big, but its connections are concise. 

This is one of the reasons why CDs and other carbonate polymers are hard and durable.

The first part of the image shows how the formation of a carbonate polymer starts. We normally draw structures in 2D for simplicity.

The second part of the image shows how big one molecule of polycarbonate can get, and what its 3D structure would look like. For comparison, the size of one carbon to another is about 0,0000000001 meter (10-10m).

These macromolecules can be formed because of many chemical and physical processes. It’s only possible because carbon has very wide capacities. Scientists are still trying to figure out its core.

CDs flammability

Polycarbonate, the main constituent of CDs, is considered heat resistant.

It’s a good electrical insulator and presents heat-resistance and flame-retardant properties.

Polycarbonate is used in many applications that require durable and strong plastic products with high melting points.

CDs can degrade under high temperatures and form pollutant gases, especially because of the phenol derivative chemicals that arise from the polymer.

A flame could appear after applying direct heat to a CD, but only a bigger fire could burn it all.

For CDs to be considered combustible, the environment around them must already be in flames, so it’s not a fire hazard. 

But enough heat could make CDs toxic.

If you wish to destroy a CD, the best thing to do is recycle it. It should be easy to do in the U.S, we don’t possess data for other countries.

Burning a CD is not a good way to destroy your data. It could be harmful to yourself and others. The best thing to do would be to shatter it, but the plastic is tough and can cut you, so attention is required. You can check some ideas here.

Conclusion

CDs are not a fire hazard. They can ignite but a lot of heat would be required to do so. Polycarbonate, the main constituent of CDs, is a polymer that has a very big carbon chain that can’t easily be burned. But toxic gases may arise from an attempt of burning.

Frequently Asked Questions (FAQS): Is _ Flammable?

Are CD discs toxic?

Not under normal circumstances. Toxic vapors can rise if a CD is melted, but a lot of heat is required to do so. Also, the CD will stop working much earlier than it melts.

Are CD discs obsolete?

Overall, yes. Digital means of storing data, clouds, and streaming services are constantly banishing the need for CDs and DVDs. But just like it happened with LP discs, many people will still want to use it, so they will probably stay around for a while.

Also, culture is always changing. CDs could make a comeback, we just don’t know about that yet.

Are CDs worth keeping?

It depends. Many people still feel nostalgic about physical means of listening to music. We never know when a nostalgic wave could hit us. Trending changes a lot, this could happen with CDs.

The more obsolete something gets, the more interesting it could get for nostalgic people and collectors. 

CDs could increase their worth in the following years. If you wish to keep your, make sure they’re stored well, their cases are being cleaned and it’s been kept away from the sun.

Can you hang up CDs?

Yes. Many people do that to try scaring birds away.

Doing so would not enhance the risk of flammability in one spot, and the CDs shouldn’t melt.

Are compact discs recyclable?

Yes. The polycarbonate component of CDs is recyclable, but it might not be available in your region. Check with e-recyclers in your area for more information.

Citations

POHLMANN, Ken C. The compact disc handbook. AR Editions, Inc., 1992.

https://en.wikipedia.org/wiki/Compact_disc
https://en.wikipedia.org/wiki/Polycarbonate
https://www.canstockphoto.com.br/structure-feito-pl%C3%A1stico-phosgene-a-17261417.html
https://pslc.ws/macrog/pc.htm
https://www.efsa.europa.eu/en/topics/topic/bisphenol

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