Construction site evacuation safety: Evacuation strategies for tall construction sites: Research report

BACKGROUND: The soaring scale of high-rise building construction – the number of projects and the size of the buildings – is reflected in the number of workers exposed to these demanding construction environments, and the potential for large-scale evacuation. In London alone, an estimated 541 highrise building projects are planned for the next few years. A typical project, such as the ￡400 million ‘100 Bishopsgate’ building, will have a peak of around 1,500 workers on site, and a cumulative workforce estimated at 12,000. The total number of workers exposed to construction sites in London during the lifetime of these 541 construction projects could easily exceed three million people. AIMS: The overall aim of the project is to improve the safety of construction site workers during on-site emergency evacuation, through the development of a unique evidence base characterising, for the first time, the actual performance and behaviour of construction workers during emergency evacuation. Combining this information with computer simulation will inform the development of more reliable evacuation procedures, improving the work environment through better preparation for, and management of, on-site emergency evacuation, and advancing the safety of construction workers. METHODOLOGY: The project consisted of four full-scale evacuation trials of two different high-rise buildings at two stages of construction, and five walking speed experiments. In total, 1,078 participants were involved in the nine trials, generating a data-set of around 2,200 data points, and information from 61 worker questionnaires. Analysis of this data produced generalised distributions for response times, walking speeds, stair speeds and ladder speeds, which were used to calibrate and validate the buildingEXODUS evacuation model. The validated model was then used to run 1,900 simulations exploring the impact on evacuation efficiency of changes to occupant response time, replacing formwork ladders with temporary stairs, and the use of hoists for evacuation. RESULTS: 31 key findings from this analysis were produced: • questionnaire analysis – eight key findings • generalised response time (RT) analysis relating to the formworks – five key findings • generalised RT analysis relating to the main building – three key findings • generalised climbing/walking speeds on ladders, temporary stairs and floor surfaces – four key findings • validation analysis – four key findings • use of the validated evacuation model to explore improvements in evacuation performance – seven key findings. CONCLUSIONS: The project has developed a unique evidence base characterising, for the first time, the actual performance and behaviour of construction workers during emergency evacuation. It consists of (i) response times for workers in the main building and the formworks, as measured from the sounding of the alarm in the main building, (ii) worker walking speeds on different types of surfaces, such as concrete, decking and decking with rebar, and (iii) worker ascent and descent speeds on temporary dogleg and parallel scaffold stairs and ladders. The data has been incorporated in the building evacuation simulation tool buildingEXODUS, providing it with a unique capability to simulate evacuation from high-rise construction sites. The performance of the software has been validated using measured data collected from the trials. The validated software has been used to explore how evacuation procedures for high-rise construction sites can be improved, including the impact of reducing worker response times, replacing ladders with temporary scaffold stairs within the formworks, and using hoists to assist in evacuation