This paper discusses a methodology for harmonizing the fire severity in fire resistance test furnaces. The presented methodology is based on the predicted results obtained from models that examined the effects of furnace depth, furnace lining material and type of fuel on the fire severity in fire resistance test furnaces using the CANIULC-S101, ASTM E l 19 and I S 0 834 time-temperature relationships. Comparisons between the predicted and measured temperature distribution in a test specimen at

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... 0 mm from the exposed side for floor furnaces lined with ceramic fibre insulation and insulating firebrick are provided. Results showed that the type of furnace lining material significantly affected the fire severity to the test specimen while the effects of furnace depth and type of fuel used in the furnace were minimal when the furnace was lined with ceramic fibre insulation. Recommendations to improve the reproducibility of the fire severity in fire resistance test furnaces for better harmonization between fire resistance test furnaces are provided.