Determination of the smoke layer interface height for hot smoke tests in big halls

Hot smoke tests are required to carry out in the site of tall halls in the Far East including Hong Kong and Taiwan. The objective is to evaluate the performance of smoke exhaust systems. In the field tests, it is difficult to determine the smoke layer interface height, especially in those tall halls with irregular shapes. A common practice is to measure the vertical temperature profile at distance away from the test fire. The position with sharp changes of vertical temperature is taken as the hot air layer interface. In addition, the N-percentage rule on the measured vertical temperature profile was also applied. There are arguments on determining the percentage N. This point will be studied in this article based on hot smoke test results in five atriums of height up to 33 m. In the field tests, a 2 MW methanol pool fire was approved to generate heat. Smoke guns were used to generate tracers for observing the smoke layer. A thermocouple tree was placed at distance away from the test fire. Visual observations of smoke layer would be compared with the positions giving sharp changes in vertical temperature profile. The N-percentage rule was also applied to determine the smoke layer interface height based on the measured vertical temperature profiles. Values of N varied from 10, 15, and 20%. In this way, elevation of the hot air layer interface can be determined even when a clear smoke layer is not observed.