Assessment of adequacy of water distribution network for fire fighting at different zones in Dhaka

Abstract

The objective of this study is to investigate the hydraulic adequacy of the existing water distribution network in the urban areas of Dhaka city for fire protection. For this purpose, four pilot areas from different operational zones of Dhaka Water Supply and Sewerage Authority (DWASA) have been selected on the basis of their development pattern. These are Baridhara DOHS, Banani Old DOHS, Niknuja and Nimtoli (a portion of old Dhaka). As an effective fire fighting device, street hydrants have been proposed with the pipe network at some suitable locations in the study area following some international standards. Besides the minimum and maximum fire-flow requirements for these hydrants have been derived from the Bangladesh National Building Code (BNBC, 2011) guidelines. As there are no well defined hydraulic specifications readily available for street hydrants in BNBC and other local standards, therefore pressure-flow constraints have been set on the basis of existing network behavior and supply characteristics. A WaterCAD v8i hydraulic network model has been developed for each area in order to perform fire flow analysis. Necessary network information and consumer demand characteristics have been collected from field survey and processed for model input. Besides, different local and international water standards such as BNBC, AWWA, ISO and NFPA have been utilized to define several model variables. Then all the models have been simulated at steady state condition for one of the worst case scenarios e.g. under peak demand period during a day. In addition, ten critical scenarios have been analyzed in each model to evaluate the system response and pressure-flow hydraulics at the hydrant locations. Simulation results dictate the Available Fire-Flow (AFF) at the hydrant nodes under different scenarios. Based on the AFF quantity, the adequacy of individual model has been assessed. Besides the most critical and most reliable hydrant locations have been also identified according to overall performance at those locations under different worse case scenarios. A total of 141 street hydrant locations have been proposed and recommended in the study areas. Among them, five in Baridhara DOHS and twenty two in Nikunja have been identified as the critical hydrant nodes. Meanwhile the network of Nimtoli is found adequate for fire fighting with thirty one hydrant locations. Note that the net AFF has been determined at individual hydrant in any of the four models in the base scenario for a minimum residual pressure of 1 m. Overall hydraulic evaluation of study areas depict that the system has reasonable adequacy for fire protection under general circumstances. Therefore, proposed fireflow nodes in the study areas can be used for detailed design, flow-rating and installation of street hydrants. This will ensure and enhance the reliability of the existing water distribution network. Besides the report also provides a comprehensive guidelines for setting a suitable fire flow water requirement which can be utilized in other parts of Dhaka city. Finally the study provides a primary technical reference for evaluation of fire fighting network in the water distribution system of Dhaka.