Assessing the risk and
consequences of failure
Decisions about the need for treatment must also take into consideration the risk and consequences of failure. One use class can cover a range of components yet the risk and consequences of failure can vary from one to another. Each component should be assigned a “service factor code” to assess the need for preservative treatment see table 2 below.
An alternative to using preservative pre-treated wood is to use modified wood or a species with a natural durability classification suitable for the use class. Details of appropriate species classified by durability and use class suitability can be found in the WPA Wood Preservation Specification Manual
Service factor codes relating to need for preservation (Source:BS8417) |
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Service factor code |
Description of risk and consequences of failure |
Need for Preservation |
A |
Negligible risk of failure |
Unnecessary |
B |
Where risk of failure is low and preservation can be regarded as an insurance against cost of repairs, and/or where replacement of timber or remedial action is not difficult or expensive. |
Optional |
C |
Where risk of failure is high and/or where replacement of timber or remedial action is difficult and expensive. |
Desirable |
D |
Where risk of failure is very high and/or where failure of timber components would result in serious danger to structure or persons |
Essential |