As for any building material, verification of fire resistance is mandatory for timber structures. While nonstandard fire design for steel members has long tradition, the corresponding possibilities for timber members are limited. Reasons for this can be found in the degree of complexity of the material and the limited research done in the field. This paper summarizes outcomes of tests, investigating the influences on the charring behaviour of timber by varying the oxygen content and the gas

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... ent and the gas velocity in the compartment. Results show that charring is depending on the fire compartment temperature, but, results show further that at higher oxygen flow, char contraction was observed affecting the protective function of the char layer. In particular, in the decay phase char contraction should be considered which may have a significant impact to Performance Based Design using non-standard temperature fire curves where the complete fire history including the cooling phase has to be taken into account.