In order to classify the timber based on durability, test specimens of size 600 × 50 × 50 mm are buried in the ground to half their lengths, for a particular time period, and the condition of the specimen at various intervals of time are noted, and their average life is computed. In order to classify the timber as high durable, the average life shall be at least:
1
120 months and above
2
greater than 30 months and less than 60 months
3
less than 30 months
4
less than 120 months but of 60 months or more