The worst thing you can do is tearing them apart. It's time consuming and attacker just needs extra time and patience to put pieces together.
The same rule applies for shredding - if after shredding are left too large pieces, again, attacker just needs time and patience.
There are several shredding techniques (from wikipedia)
- Strip-cut shredders, the least secure, use rotating knives to cut narrow strips as long as the original sheet of paper. Such strips can be reassembled by a determined and patient investigator or adversary, as the product (the destroyed information) of this type of shredder is the least randomized. It also creates the highest volume of waste inasmuch as the chad has the largest surface area and is not compressed.
- Cross-cut or confetti-cut shredders use two contra-rotating drums to cut rectangular, parallelogram, or diamond-shaped (or lozenge) shreds.
- Particle-cut shredders create tiny square or circular pieces.
- Cardboard shredders are designed specifically to shred corrugated material into either strips or a mesh pallet.
- Disintegrators and granulators repeatedly cut the paper at random until the particles are small enough to pass through a mesh.
- Hammermills pound the paper through a screen.
- Pierce and Tear Rotating blades pierce the paper and then tear it apart.
- Grinders A rotating shaft with cutting blades grinds the paper until it is small enough to fall through a screen.
Also, there are several standards for shredding (from wikipedia)
- Level 1 = 12 mm strips OR 11 x 40mm particles
- Level 2 = 6 mm strips OR 8 x 40mm particles
- Level 3 = 2 mm strips OR 4 x 30mm particles (Confidential)
- Level 4 = 2 x 15 mm particles (Commercially Sensitive)
- Level 5 = 0.8 x 12 mm particles (Top Secret or Classified)
- Level 6 = 0.8 x 4 mm particles (Top Secret or Classified)
What I'm trying to say is - it's not about - "Let's torn this paper and we'll be fine!" It's about how hard is to put this pieces together. If it's next to impossible, then shredding is done well.
However, if attacker is aiming for the lowest hanging fruit, then any kind of shredding is better then none.
Example of well done shredding (once it was a money)
I guess setting them on fire or destroying them in chemical reaction would be the fastest, but this techniques should only be preformed in controlled environments by professionals!!!
Alternative is to decompose paper in water, however, it's pretty long process (10-14 days) and you'll need enough space and water to do so.