According to DIN 68.800-3:1990-4 – wood preservation; preventive chemical wood preservation, the following test marks can be assigned to a wood preservative:

Iv

preventively effective against insects

P

preventively effective against fungi (fungal decay)

W

also for wood that is exposed to weather influences, but that is not in constant ground contact and not in constant water contact

E

also for wood, that is exposed to extreme conditions (in constant ground and/or water contact as well as debris in fissures and splices)

Ib

curatively effective against insects

M

prevents the growth of dry rot through masonry

The requirements for wood preservatives differ depending on the hazards the supporting wood components are exposed to::

Hazard Class O

Wood in interior use, which is constantly dry, is not exposed to hazards.
It does not have to be impregnated with a wood preservative.

Hazard Class 1

Under certain circumstances wood in interior use has a certain risk of being exposed to insects. In this case, it is necessary to treat the wood with a wood preservative that has the test mark Iv.

Hazard Class 2

Wood that is not in ground contact nor is directly exposed to weather influences or leaching (temporary wetting is possible) has to be treated with a wood preservative that has the test marks P and Iv.

Hazard Class 3

Wood that is not in ground contact, but is exposed to weather influences or condensation has to be treated with a wood preservative with the test marks P, Iv, and W.

Hazard Class 4

Wood that is in constant ground contact or permanently exposed to wetting has to be impregnated with a wood preservative with the test marks P, Iv, W, and E.

Supporting wood components that are exposed to hazards according to hazard classes 1-3 can be impregnated using trough impregnation.

For wood in hazard class 4, sufficient protection can only be achieved using vacuum pressure impregnation.