Evaporation as an ageing procedure prior to wood preservativebiological testing: when standardization needs metrology

Abstract

The wood preservation laboratory of Cirad is accredited by COFRAC (French accreditationcommittee – accreditation No. 1-1686) for tests on (1) durability of wood and wood-basedproducts; (2) protective efficacy of wood preservatives; (3) efficacy of termite controlproducts. In order to test the efficacy of wood preservatives, non-durable wood blocks aretreated using different product doses and exposed to the attack of xylophageous organisms(fungi, insects). To reproduce the ageing of treated wood blocks, some laboratoryprocedures are available. Amongst them, there is an evaporation procedure, reproducing theaction of a warm air flow onto treated wood. This ageing step is very discriminant, asonly the formulations fixing effectively the active ingredients will pass the biologicaltest afterwards. This ageing by evaporation is described in the EN73 standard.Nevertheless, many points remain difficult to overcome. The tunnels used for theevaporation are all prototypes; as such equipment is not available currently on themarket. So each laboratory has got its own tunnel device. Moreover the way to measure thetemperature and speed of the air flow is very difficult to achieve considering theprescriptions of the EN73 standard. The EN73 standard is being revised by the Europeanstandardization group (CEN TC38) and despite the metrological aspects were crucial andinadequate in former version, they were not considered as they should. The woodpreservation laboratory has forwarded remarks in order to supersede some points of therevision document in order to consider the metrological aspects. This is of mainimportance as the ageing procedure is commonly used prior to most of the biological test,and such tested products are put on the market based on the efficacy results.