Destroying CDs, DVDs and Blu-rays safely: why scratching does not help
The era when backups, installations and presentations were shared on optical discs seems to be past, but archive cupboards still hold them in their masses. Patient files, customer backups, confidential photo sessions, presentation decks from acquired companies. A drawer full of old CDs and DVDs remains a data store as long as the discs are readable. And they remain readable, even with scratches.
Why snapping in half does not work
Breaking a CD produces two half discs, each with sizable readable surfaces. Forensic labs have read damaged optical discs for years using polishing machines and specially modified drives. Scratches on the top often do not reach the reflective layer, so the data under the polycarbonate stays untouched. Putting them in a microwave does physically work, but produces enormous fumes from burning reflective and adhesive layers, plus damage to the microwave itself. None of these methods gives you audit evidence.
How an optical disc is built
A disc is a sandwich:
- Polycarbonate substrate (1.2 mm). The transparent plastic the laser reads through.
- Reflective layer. Aluminium on CD/DVD, sometimes silver or gold on archive discs.
- Pit-and-land pattern. The physical microscopic bumps that represent the bits.
- Protective lacquer and label. On the top side.
The data therefore sits deeper in the disc than many people think, just under the reflective layer. A scratch on the top side that only damages the label does not even touch the bits.
DIN 66399 O-classification
The DIN 66399 standard has its own O-scale for optical discs. The relevant levels for business data:
- O-3: particles up to 160 mm². Suitable for general business data without special-category personal data.
- O-4: up to 30 mm². The standard level for customer records and internal data.
- O-5: up to 10 mm². For special-category personal data, such as medical files or professional secrecy.
- O-6 / O-7: 5 and 0.2 mm². For classified and defence material.
For most Dutch organisations O-4 is more than enough. For healthcare, legal and notarial practice, O-5 is the defensible level.
How it works in practice
An industrial optical-disc shredder works with fine cutting rollers and a sieve construction that only releases particles once they are small enough. The CD or DVD is fed through the slot, the disc falls apart into a handful of shards a few millimetres in size, and those shards are collected on a conveyor in a sealed container. Comparable to how we dispose of USB sticks and memory cards, with the difference that the cut size for optical discs is allowed to be slightly larger than for solid state.
When even O-5 falls short
For so-called mass-storage archive on LTO tape, different rules again apply, because the cassette and the tape each have their own destruction requirements. We wrote about that earlier in clearing out backup tapes and LTO. With mixed batches (a box with CDs, DVDs and LTO cartridges), you ideally split per type, because optical discs and magnetic tape do not belong in the same shredder.
What to do with the old inventory?
- Inventory. Inventory in boxes, label per type (CD, DVD, Blu-ray, LTO). No standalone identification per disc needed, but per box.
- Choose a classification. Determine the minimum DIN O-level based on content.
- Plan a pickup day. Ideally together with your paper or HDD destruction so you make use of one pickup.
- Supervision. At O-5 or higher, on-site destruction is recommended.
- Keep the certificate. With count or weight, media type and DIN level.
Stacks of old CDs and DVDs in the archive cupboard?
We destroy optical discs on-site to DIN 66399 O-4 or O-5, with a certificate. Feel free to combine with your paper archive in one pickup.
Request a quoteNot sure which DIN O-level fits your content? Ask for advice via desnipperaar.nl. We advise proportionally, no more expensive than needed.