This paper describes a semi-quantitative analysis used for a sprinklered high rise building. Itwas shown that instead of the mandatory placing of fire resistant glazing in the fa?ade the same levelof safety could be attained by a relatively simple and cheap improvement of the sprinkler system.In many countries, a minimum vertical separation of openings in fa?ades is prescribed to limit the riskof vertical fire spread through wall openings. In the Netherlands the use of a standardized engineeringtool is mandatory for assessing the risk of external vertical fire spread between fire compartments.The case reviewed is a 150 metre high rise office building. The results of the vertical fire spreadcalculations for this building would translate into costly measures in the fa?ade.DGMR Consulting Engineers developed a semi-quantitative probabilistic model to evaluate whetheralternative measures, such as adding redundancy in the sprinkler system, would be more cost effectivewhen reaching the same or even a higher level of safety in terms of area affected by fire. By agreementwith the authorities it was recommended to apply measures in the fa?ades on a limited number offloors only.In the described method the expected affected (damaged) area is taken as a measure of the risk of firespread. Event trees are used to compare the fire safety level of different scenarios with differentprecautionary measures. The semi-quantitative approach makes it possible to use engineeringestimates, and to focus on the effects of the compared measures only, in order to consider which ofthese measures is most (cost) effective. The method proves to be little sensitive to the value of theestimated probabilities and can be used to evaluate the effect of organizational, structural or electrotechnical measures in a building.
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