Predicting the Fire Source Location by Using the Pipe Hole Network in Aspirating Smoke Detection System

Overview

ASD systems (VESDA-type) draw air from the protected area through a sampling-pipe network into a central sensing chamber, which suits environments where point detectors struggle, such as hot-aisle containment and cold warehouses operating from 8 °C to -40 °C. The study investigates the effect of the pipe hole network on obscuration at the detector: a Pipe Hole Network Program computes pressure drop, flow split and transport time hole by hole, and was compared with experiments on a 20 m pipe with 10 or 20 sampling holes and a smoke box placed at each hole.

The test pipe was 20 m long with ten 5 mm sampling holes at 2 m spacing, and a 20-hole variant was also studied. Because air from clean holes dilutes the sample, obscuration at the detector falls sharply the farther the smoke source is and the more holes there are. With 5%/m obscuration in the smoke box on the 20-hole pipe, obscuration at the detector was about 0.68%/m when smoke entered hole 1 but only 0.045% when it entered hole 20. Increasing the number of holes decreased the obscuration reaching the ASD.

Numerical results followed the same trend as the experiments, so the network program can be used to predict obscuration at the detector. Correlations between slope, obscuration ratio and fire source location were derived as length equations, from which a normalised length can be calculated and the fire source location predicted.

Limits: the correlations were developed for short pipes only and chamber obscurations of 5, 10 and 15%/m; real-fire obscuration varies with time and needs further work, including machine learning. The result is a first step toward ASD systems giving rough location information as well as an alarm.

Key points

1. ASDs are presented as suitable where conventional detectors cannot be applied, including hot-aisle areas and cold warehouses operating from 8 °C to -40 °C.
2. Test pipe: 20 m long with ten 5 mm sampling holes at 2 m spacing; a 20-hole variant was also studied.
3. With 5%/m obscuration in the smoke box on the 20-hole pipe, obscuration at the detector was about 0.68%/m when smoke entered hole 1 but only 0.045% when it entered hole 20.
4. Increasing the number of holes on the pipe decreased the obscuration reaching the ASD.
5. Numerical results followed the same trend as the experiments, so the network program can be used to predict obscuration at the detector.
6. The correlations were developed for chamber obscurations of 5, 10 and 15%/m on short pipes only; real-fire obscuration varies with time and needs further work.

Using it in design

• In ASD pipe network design, account for dilution of obscuration by hole count and distance from the detector; for long, many-hole pipes, verify time to alarm threshold and sensitivity by calculation.
• For ASD in hot-aisle containment, calculate the pipe hole network and transport time hole by hole before fixing the pipe layout.
• Consider these correlations for fire-location estimation only on short pipes and within the tested obscuration range; ask for added verification for time-varying obscuration in real fires.

Who should read it

Fire detection engineers designing aspirating smoke detection pipe networks for data centres and cold stores.

Document contents

1. 1. Introduction
2. 2. Theoretical Analysis (2.2 Obscuration)
3. 3. Numerical and Experimental Studies (3.1 Numerical study: mathematical model, numerical setup; 3.2 Experimental Study)
4. 4. Results and Discussion (including 4.2 ASD System with One Branch Pipe with Twenty Holes)
5. 5. Conclusions

Related standards

• EN 54-20
• NFPA 72
• NFPA 75

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Publication details

Authors

Young Man Lee; Ha Thien Khieu; Dong Woo Kim; Ji Tae Kim; Hong Sun Ryou

Publisher

Applied Sciences (MDPI AG)

Year

2022

Volume

12

Issue

6

Pages

2801

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/app12062801

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation