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When destroying hard drives, SSDs and USB sticks, one number decides security: the particle size. The smaller the pieces, the more hopeless any attempt to reconstruct data. This entry explains what the DIN 66399 standard specifies and why flash memory needs smaller particles.

What does particle size mean under DIN 66399?

DIN 66399 regulates the destruction of data carriers. It works with three components: protection class, material class and Security level. The security level describes how finely material is shredded. In the higher levels, this is done via a maximum particle area. The area of a single piece is measured, not its weight or volume. Since 2018 the standard has also existed as the international standard ISO/IEC 21964.

The type of data carrier is important. A hard drive (material class H) stores data magnetically on large platters. An SSD or USB stick (material class E) stores a great deal of data on tiny flash chips. A particle that contains only a small piece of platter in a hard drive can contain an entire chip in an SSD. That is why the limits for class E are significantly stricter.

Particle sizes for hard drives and flash memory

Level	Hard drives (H)	SSD and flash (E)
1	Data carrier is inoperable	Data carrier is mechanically or electronically inoperable
2	Functional parts damaged	Data media shared
3	Data carrier deformed	≤ 160 mm²
4	Deformed several times and cut, ≤ 2,000 mm²	≤ 30 mm²
5	≤ 320 mm²	≤ 10 mm²
6	≤ 10 mm²	≤ 1 mm²
7	≤ 5 mm²	≤ 0,5 mm²

For comparison: 320 mm² corresponds roughly to the area of a postage stamp. For paper, optical media, magnetic tapes and microfilm, the standard defines its own values. The guide DIN 66399: Which safety level your hard drives need shows how to combine protection class and level.

What you should pay attention to

• Consider H and E separately: An SSD that has only been shredded to an H level may contain intact memory chips.
• Have the level confirmed in writing: The certificate of destruction should state the material class and security level.
• Device and method must match: One Hard drive shredder achieves only the level for which it is built. For very small particles, fine shredders or a Disintegrator are used.
• Check the erasure: Functioning data carriers can often be erased with certification and reused. This saves resources and generates revenue.

Particle size at Second IT

Second IT destroys data carriers in-house in accordance with DIN 66399, certified for security level H-5. Hard drives are shredded into particles of at most 320 mm². The area is video-monitored, every data carrier is recorded by serial number, and you receive a certificate of destruction. More on in-house data carrier destruction.

Frequently asked questions about particle size

What particle size does security level H-5 have?

For hard drives of material class H, level H-5 permits particles with an area of at most 320 mm². That corresponds to roughly the area of a postage stamp.

Why do SSDs need smaller particles than hard drives?

SSDs store data on small flash chips with very high data density. A larger piece can contain an entire, readable chip. That is why significantly smaller limits apply to material class E.

Is particle size measured as area or volume?

DIN 66399 specifies the particle size for hard drives and flash memory as a maximum area in square millimeters. For paper, additional requirements on strip width apply for some levels.

What do material classes H and E mean for particle size?

H stands for hard drives, which store data magnetically on large platters. E stands for electronic data carriers such as SSDs and USB sticks with tiny flash chips. Significantly stricter limits apply to class E than to class H.

What particle size does security level E-5 have for SSDs?

At security level E-5, a particle may be at most 10 mm² in size. For comparison: level H-5 for hard drives permits 320 mm². The certificate of destruction should state the material class and security level.