Utilisation of statistics to assess fire risks in buildings
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ESPOO 2004ESPOO 2004ESPOO 2004ESPOO 2004ESPOO 2004 VTT PUBLICATIONS 537
Utilisation of statistics to assess firerisks in buildings
In this work, the elements relating to fire risks in buildings are examined onthe basis of the statistical data in the national accident database Pronto. Asa result, valuable new information related to fire risks in buildings isobtained and quantitative methods for risk assessment are presented. Thework concentrates especially on the ignition frequencies of buildings,economic losses due to building fires and the operation of fire departments.
VTT PUBLICATIONS 537
Utilisation of statistics to assess fire risks in buildings
Kati Tillander VTT Building and Transport
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Civil and
Environmental Engineering for public examination and debate in Auditorium R1 at Helsinki University of Technology (Espoo, Finland) on
the 1st of July, 2004, at 12 noon.
ISBN 9513863921 (soft back ed.) ISSN 12350621 (soft back ed.)
ISBN 951386393X (URL: http://www.vtt.fi/inf/pdf/) ISSN 14550849 (URL: http://www.vtt.fi/inf/pdf/)
Copyright VTT Technical Research Centre of Finland 2004
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Tillander, Kati. Utilisation of statistics to assess fire risks in buildings. Espoo 2004. VTT Publications 537. 224 p. + app. 37 p.
Keywords fire risk, building fires, fire safety, statistics, ignition frequency, economic losses, fire department
Abstract This study is the first relatively broad statistical survey utilising the statistical data collected in the national accident database, Pronto. As a result valuable new information relating to fire risks is obtained and quantitative methods for fire risk assessment of buildings are presented. This work is a step forward in the field of risk-analysis-based fire safety design and overall a step towards a better understanding of the anatomy of fires.
The use of statistical information is a good objective way of attempting to characterise fires. This study concentrates on ignition frequency, economic fire losses and fire department operation in the event of building-fires. Ignition frequency was derived as a function of total floor area for different building categories. The analysis showed that the variations of ignition frequency are dependent on initial floor area distributions of the buildings hit by fire and at risk. For engineering design purposes, the generalisation of the theory starting from the initial floor area distributions, leading to a sum of two power laws, was found suitable. The parameters and partial safety coefficients for the model were estimated for three building groups. The model is suitable for determining the ignition frequency of buildings with a total floor area of between 100 and 20 000 m2.
The elements describing the fire department operation were analysed on the basis of statistical information. In the presented approach, the buildings in which fire safety depends completely on automatic extinguishing systems can be distinguished from those in which the fire department is able to arrive at the fire scene early enough to have a good chance of saving the building. The most important factor affecting the performance of the rescue force was found to be the travel time to the fire scene. Thus, to make the task easier for the fire department, special attention must be paid to rapid fire detection and locating of
the fire seat. Delays in these actions lengthen the total response time and reduce significantly the chances of the fire department successfully intervening in the progress of the fire.
Economic losses were considered as consequences of the fires. The analysis showed the dependency of loss and value-at-risk of the building on the floor area. Clear local peaks were detected for both the ignition frequency and fire losses. A more detailed analysis of residential buildings where the phenomenon was most apparent revealed that the peaks were located around the floor-area region where the dominant building type of the building stock, and thus the compartmentation manner, changed. With small values of the total floor area of the building, the rise of the loss was very steep, but levelled off to substantially slower growth with large values. A natural explanation for the behaviour is compartmentation. Both the ignition frequency and the fire losses should therefore be examined in relation to the size of the ignition compartment, which would be a significantly more appropriate descriptor than the total floor area of the building. Hence, it is essential that the information becomes available to the Finnish accident database, in which it is not at the moment included. The analysis shows that the type of building and compartmentation, rather than the material of the load-bearing member itself, was the factor having the greatest effect on the risk of fire.
The use of the information gathered was demonstrated through a simple example case in which the fire risk was assessed using the time-dependent event-tree approach.
This study concentrates on the utilisation of statistics to collect information and gain an understanding of the elements affecting fire risks in buildings. Many of the methods used are well known in other application areas; the available statistical data now offers the possibility of applying them in connection with fire-risk problems as well. In risk-analysis-based design, the presented approach is very useful and the methods can be used for fire-risk assessment of buildings. Nevertheless, this study should be considered the first part of a major research effort and further studies will be needed to improve the tentative models to obtain more detailed and reliable risk estimates. In this work a preliminary exploration is carried out and a good base for further research is established.
Preface This work has been carried out under the auspices of the Technical Research Centre of Finland (VTT) and Helsinki University of Technology (TKK) with the financial support of the Helsinki University of Technology, Academy of Finland and Tekniikan edistmissti.
I wish to acknowledge Docent Olavi Keski-Rahkonen for his guidance and encouragement during this work. I am most grateful to Esko Mikkola for his support and advice. I also wish to thank Dr. Jukka Hietaniemi for his valuable comments during the completion of this thesis.
Furthermore, I wish to thank my colleagues in the fire research group of VTT Building and Transport for their helpful attitude towards my questions and for creating a pleasant working environment.
Finally, I wish to express my sincere gratitude to my family and friends for their endless support, encouragement and understanding, which have carried me through the difficult times during this work. I am deeply grateful to my closest ones for bearing my ups and downs, for enduring the endless discussions with me and for constantly encouraging me at those times when it seemed impossible to go on. Thank You!
Espoo, August 2003
Authors contribution The work presented in Sections 57 was carried out in co-operation with the supervisor of this thesis, Docent Olavi Keski-Rahkonen. Some of the results are presented in Finnish in a series of VTT Research Notes and journal articles, in addition to three conference proceedings in English. The related articles, not all of them published, are mentioned at the beginning of each section and referred to in the body of text. The research methods used in Sections 57 were based on the ideas suggested by Docent Keski-Rahkonen. The author had the main responsibility for carrying out the statistical analysis, validation of the models and interpretation of the results under the supervision of Docent Keski-Rahkonen. The author also had the main responsibility of writing all the collaborative reports, publications and conference papers, as well as of conference presentations.
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