Influence of high altitude on the burning behaviour of typical combustibles and the related responses of smoke detectors in compartments.

Ran Tu,Yong-Ming Zhang,Jun Fang,Yi Zeng

doi:10.1098/rsos.180188

Abstract

The effect of altitude on typical combustible burning and related smoke detector response signals was investigated by comparison experiments at altitudes of 40 m and 3650 m based on EN54 standard tests. Point-type light scattering photoelectric smoke detectors and ionization smoke detectors were used for four kinds of EN54 fire tests, including two kinds of smouldering fires with wood (test fire no. 2 in EN54 standard or TF2) and cotton (TF3), and two kinds of flaming fires with polyurethane (TF4) and n-heptane (TF5). First, the influence of altitude or ambient pressure on mass loss for smouldering combustion (TF2 or TF3) was insignificant, while a significant decrease in the mass burning rate was found for flaming tests (TF4 and TF5) as reported in our previous studies. Second, for photoelectric smoke detectors in flaming fire tests, the effect of altitude was similar to that of the burning rate, whereas for the ionization smoke detectors, the response signal at high altitudes was shown to be ‘enhanced’ by the detection principle of the ionization chamber, leading to an even larger value than at normal altitude for smouldering conditions. Third, to provide a reference for smoke detector design in high-altitude areas, the differences between signal speed in rising and peak values at two locations are discussed. Also, relationship between ion chamber signals and smoke optical densities are presented by utilization of an ionization smoke detector and smoke concentration meter. Moreover, a hierarchical diagram is illustrated to provide a better understanding of the effects of altitude on combustible burning behaviour and the mechanisms of detector response.

Highlights

Interest in fire detection engineering in high-altitude areas stems from the need to protect both the local populace and historic buildings
Flame or plume physical characteristics and temperature profile have been proved to be affected by pressure obviously [7,9,10,11]
The actuation times of both Pho and Ion detectors, which started around 1000 s, are shown to be seriously delayed compared to the mass loss shown in figure 4a. This was caused by the slow smoke movement driven by low temperature buoyancy, which made it even more difficult for the smoke to reach the ceiling due to the cooling effect of the ambient cold air

Summary

Introduction

Interest in fire detection engineering in high-altitude areas stems from the need to protect both the local populace and historic buildings One such area is the Qinghai-Tibet Plateau in China, with an average altitude of 4 km. It is called the roof and the third pole of the world and contains thousands of historic buildings, including the Potala Palace. Environment parameters such as humidity, air pressure and temperature can significantly influence fire dynamics and burning behaviour [1,2,3,4,5,6,7,8,9,10,11,12,13]. Smoke formation, concentration and movement would change, which introduces new challenges for smoke detectors used in these areas

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Conclusion