Node Network Computer Modelling and a Simple Hand Calculation Compared with Contemporary High Rise Evacuation Case Study Data

Abstract

Tall buildings are becoming more common in the modern built environment and the method of evacuating or moving to a place of safety using the stairs is still the primary means of egress. Typically designers use tools such as computer models and hand calculations to predict the time taken for occupants to evacuate to an exit or place of safety. However, increasing trends of obesity, age and a sedentary lifestyle is raising questions about the accuracy of some of the tools. As the tools are based on case study data carried out in the 1980’s.

This research compares evacuation performance of case study buildings to the predictions by Pauls’ simplified hand calculation and the EvacuatioNZ computer model. The comparison uses four multi-storey buildings from the case study data, ranging from 11 to 27 stories high. The research will also investigate the effect of how the building is represented in EvacuatioNZ on the performance of the prediction and make recommendations in best practice for further work.

Results from the comparisons shows EvacuatioNZ is within 15% for total egress time of the case study data in six out of eight of the stairs. The average difference of EvacuatioNZ to the case study is 8.6%. Further comparisons of exit flow rate and descent speed show EvacuatioNZ is within 10% of the case study data in five out of eight of the stairs. Paul’s simplified hand calculation predicts a total egress time which is 6% to 38% shorter than the case study data. Modifying the equation to equalise stair entry delay improves the prediction to a difference of 0.9% to 31%. The modified equation is within 10% in five out of eight stairs.

The comparisons for EvacuatioNZ indicate predictions which are generally with 10-15%. However individual performance is not investigated and this area should be fully investigated to answer concerns about contemporary occupants and their ability to descend multiple flights of stairs. Further work should include a larger range of data, particularly exploring building height and population.

Given the recommendations are followed and more data becomes available for further work to support this research; EvacuatioNZ could be used as a tool for predicting evacuations in multi-storey buildings. Pauls’ hand calculation is not recommended for predictions of multi-storey evacuations without a safety factor. Differences between the prediction and case study result were improved with a modification of the equation to account for the case study stair entry times.