Calculation of charring rate and char depth of spruce and pine wood from mass loss

A charring rate is a key parameter for the calculation of fire resistance of timber structures and for fire investigation. Charring rates are calculated from the char depth, and the time material is exposed to the heat load. The presented study deals with the calculation of the char depth of Norway spruce (Picea Abies (L.) Karst.) and Scots pine (Pinus Sylvestris L.) wood from the mass loss during the test on a cone calorimeter. The samples were loaded with the heat fluxes of 20, 30, 40 and 50 kW m−2 during a period of 10, 20 and 30 min. The samples were extinguished after the stated time intervals and subsequently the char depth was measured. The mutual orientation of the grain and the incident heat flux was parallel. A strong linear relation was found between the char depth and the ratio of the mass loss to density. The average charring rate decreases with the increasing time and increases with the increasing heat flux. The average charring rate of spruce wood was in the interval from 0.73 to 1.5 mm min−1. The average charring rate of pine wood was in the interval from 0.67 to 1.3 mm min−1.