An overestimation of performance will almost always result if the condition of a specimen is considered to be attained at the precise time that an inspection is carried out. The time at which the condition is actually attained, referred to in this document as the "Condition time", is best considered to be halfway between two successive inspections. The requirement to obtain data that is relevant to the condition time may be overlooked by persons planning an inspection schedule, but the intervals for inspection are critical when expected class limits (such as time limits for performance of different classes of natural durability) have to be addressed. This paper discusses appropriate inspection procedures for both future CSIRO tests of natural durability and, more precisely, relevant to Standard pr. EN 350 Part 1. These proposed procedures are all based on the determination of median specimen life values rather than mean specimen life.

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