Study of Effectiveness of CO and Smoke Alarm in Smoldering Fire
Authors: Hadano Hironori , Nagawa Yoshiharu , Doi Toshiyuki , Mizuno Masayuki 
Published: May 2020

Introduction

One of the main causes of home fires in Japan is smoking in bed, and carbon monoxide poisoning and suffocation account for a high proportion of cause of death in bedding fires [1]. In this study, using a full-scale building model, a smoldering fire initiated with a lighted cigarette placed still on cotton bedding was reproduced. The COHb concentration (blood COHb concentration) inhaled into a human body and the density and concentration behavior of smoke and CO alarms were compared by monitoring the change in the CO concentrations while smoldering fire. Early detection of fires and effects on a human body were discussed based on the data and the effectiveness of a smoke and CO alarm placed on an indoor wall was examined.

Experimental

In this study, single function CO gas sensor modules and smoke and CO alarms equipped with photoelectric smoke detectors and electrochemical CO sensors were arranged in a full-scale building model, as shown in Figure 1. Smoldering fire was caused in cotton bedding using a cigarette as a source of fire, and the COHb concentration of an expiratory position and the smoke densities and the CO concentrations of smoke and CO alarms placed on walls were examined. The laboratory was W2.12 ×D2.58 × H2.42 m (13.23 m3 in volume) and a set of cotton bedding was arranged. The source of the fire was set almost at the center of the laboratory and the CO sensor modules were arranged at the pillow, in the bedding, and on the upper part of the bedding (L1-300～L5-400), and on the lower part of the ceiling (L1-2120～L5-2120). Also, smoke and CO alarms (A1～A4) were placed 300 mm off the ceiling on the four walls of the laboratory. The CO concentration outputs and smoke density outputs at each measuring point were collected per 5 seconds using data loggers. After the lighted cigarette (MEVIUS SUPER LIGHTS) was placed still, each measured data was being continuously monitored. Also, based on the CO concentration data from the CO sensor modules surrounding the bedding, the COHb concentration accumulated in a human body was calculated.

Result and Conclusions

Each CO concentration data from the CO sensor modules placed 400 mm above the lower part of the mattress, in the bedding, and at the expiratory position were extracted as representative data (Fig.2). The CO concentration right above the fire point started rising 50 seconds after the cigarette was placed still, sharply surged to a high concentration level over 1000 ppm at 440 seconds. The CO concentration under the coverlet also suddenly surged a bid later than the one right above the source of the fire, exceeding 1000 ppm at 350 seconds. For the CO concentration at position near the pillow as expiratory position, the rise of CO concentration was confirmed 380 seconds after the cigarette was placed still and the concentration exceeded 1000 ppm at 1240 seconds. Figure 3 shows it is sufficiently possible to detect CO on the wall’s position since it was found in the comparison of the data of the CO sensor module near the ceiling and the smoke and CO alarms on the laboratory walls that the trends of CO concentration were similar in terms of the ways of rising and the concentration values. In this experiment, assuming a respiratory position of a sleeping person, the COHb concentration accumulated through breathing based on the CO concentrations of the upper part of the bedding (L2-300～L5-400) and the CO concentrations and smoke densities of the alarms placed on the walls were compared. Here, the smoke and CO alarms were set to at 10%/m for smoke and 100ppm for CO. Figure 4 shows the relationship between the CO concentration and smoke density values of A2 which responded last among the alarms placed on the walls and the COHb concentrations of the pillow position was related to these data. The smoke and CO alarms went off before the COHb concentrations exceeded 20% at the assumed human respiratory position, revealing that an alarm goes off before human life is threatened. On the other hand, a previous report has already pointed out the danger that smoke and CO flow through a comforter to a pillow position and a sleeping person directly inhales highly concentrated CO [2]. The COHb concentration at the pillow position in the case of this extremely dangerous situation was calculated and it was found that the concentration was 15.1% when the smoke alarm went off and 6.1%. Also, it took 1275 seconds for a smoke alarm to go off after the cigarette was placed still while it took 995 seconds for a CO alarm, revealing that the CO alarm detected 280 seconds faster than the smoke alarm. From the results above, it has been confirmed that the CO detection function of a CO and smoke alarm placed on a wall enables people to evacuate well in advance and the alarm is effective in early detection of fire.

References

[1] Fire and Disaster Management Agency: The 2016 White Paper on Fire Service. (2016).
[2] Oigawa et al.: Experriments on CO Generation and Propagation by Smoldering of Futon in Residential Room Model (Part 2), Summary of Research Presentation of Japan Association for Fire Science and Engineering. (2015)68–69.

Figure 1