EN 335 – 3 : 1995
Durability of wood and wood-based products Definition of hazard classes of biological attack
Part 1: Application of wood-based panels4.3.1 Hazard class 1
In this environment, OSB have a moisture content no higher than that which would result from exposure to an air temperature of 200 C on a relative humidity of 65% for practically whole of their service life. They may therefore be regarded as being dry and thus the risk of attack by surface moulds or by staining or wood-destroying fungi is insignificiant.
Due to the specific structure of OSB, there is no risk of attack by wood-destroying insects, excepts termites.
4.3.2 Hazard class 2
In this environment, the moisture content of OSB panel, either in the whole or only in part, can occasionally obtain or exceed that which would result from exposure to an air temperature of 200 C on a relative humidity of 90 % . The moisture content can therefore occasionally increase to a level which can allow the growth of wood-destroying fungi.
For panels the use of which includes decorative function, disfigurement can also occur as a result of the growth of surface moulds and staining fungi.
Risk of insect attack is similar to that for hazard class 1.
4.4.3 Hazard class 3
In this environment, OSB can frequently have a moisture content above 20% and thus will often be liable to attack of wood-destroying fungi.
For panels the use of which includes decorative function, disfigurement can also occur as a result of the growth of surface moulds and staining fungi.
Risk of insect attack is similar to that for hazard class 1.
4.4.4 Hazard class 4
In this environment, OSB have a moisture content permanently above 20% and thus will often be liable to attack of wood-destroying fungi.
Risk of insect attack to the above ground or water portion of components is similar to that for hazard class 1. Termites can be additional problem in certain geographical regions.
At present, no suitable OSB are manufactured for use in this hazard class.
4.4.5 Hazard class 5
In this environment, OSB have a moisture content permanently above 20% and are wholly or partially submerged in salt water. Attack by invertebrate marine organismus is therefore the principal problem. They can cause damage. In addition OSB are liable to attack of wood-destroying fungi.
Risk of insect attack to the above ground or water portion of components is similar to that for hazard class 1. Termites can be additional problem in certain geographical regions.
At present, no suitable OSB are manufactured for use in this hazard class.
