Determination of the Smoke Layer Interface Height for Hot Smoke Tests in Big Halls

Abstract

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.

Experimental study of the combustion characteristics of methanol‐gasoline blends pool fires in a full‐scale tunnel

“…The interface heights for M65, M85, and M100 could not be observed because there was little smoke generated during the combustion of these 3 fuels. The correlation coefficient for N = 26 was 0.8835, which shows that the N‐percentage rule method is suitable for determining the smoke layer interface height of different blends during tunnel fires, which is different from Cooper et al and Zhang et al (N = 10), Chow (N = 10, 15, 20), He et al (N = 15), and Tilly et al (N = 30).…”

“…Cooper et al proposed the N‐percentage rule to determine the smoke layer interface height, which defines the interface height as the distance from the ground to where the excess temperature is equal to N% of the maximum excess temperature in the vertical direction. Thus, the interface height can be expressed as with different N (such as 10, 15, 20, or 30) used for different fire scenarios …”

“…The smoke layer interface height is a significant parameter being directly related to life safety. Much methods [18][19][20][21][22][23] were studied to predict the smoke layer interface height. Visual observations of the interface height are often used, but the interface is difficult to see with clean fuels that produce little smoke.…”

“…with different N (such as 10, 15, 20, or 30) used for different fire scenarios. 18,[20][21][22][23] Thus, the purpose of this analysis is to study the combustion characteristics of blends pool fires in a full-scale tunnel, especially the effects of azeotropism on methanol-gasoline blends pool fires, the combustion regime in a tunnel, and the determination of the smoke layer interface height. A series of experiments with blends were conducted in a full-scale tunnel with natural ventilation condition.…”

Experimental investigation on smoke spread characteristics and smoke layer height in tunnels

“…For example, Cooper et al proposed an N percentage method for determining the smoke layer height. However, the selection of the N value would be subjective, ie, the N value varieties for different scenarios . He et al proposed the integral method and the least squares method for determining the smoke layer height, while Gao et al verified the effectiveness of the buoyancy frequency method.…”