Open kitchen fires, tall buildings, heat release rate
Many small units of area less than 30 m2 in residential buildings over 200 m tall are equipped with open kitchens in Asia, including Hong Kong. Fire safety provisions of these kitchens are determined by performance-based design (PBD). In most PBD projects, only the spread of smoke from the kitchen on fire to the outside was commonly studied. However, a fire load survey in Hong Kong indicated large quantities of combustibles are stored in residential units. Cooking oil was found to be ignited easily even when using induction cookers. The burning of all combustibles in a big post-flashover fire needs to be studied. Data of heat release rate for local combustible products is not yet available. Estimations are based on very crude assumptions of low radiative heat flux in most of the PBD projects, and they are not supported by full-scale burning tests. Three conditions are therefore imposed by the authorities in the design approval. Firstly, gas cookers cannot be used; only flameless electric induction cookers are allowed. Secondly, additional fire suppression systems, including water mist or dry powder systems, are specified for installation. The systems are supposed to act on the stove fire and prevent its growth. The residential unit owner cannot remove the system, nor change the cooking stove without approval from the government. Thirdly, the estate management office has to sign an undertaking to implement the fire safety management procedures specified in the PBD report. However, the fire behaviour of open kitchen in small units of tall buildings is not studied in detail. No comparison has been made between scenarios with and without fire resisting enclosures. Fire dynamics is not well understood in open kitchen fires inside a small unit. Full-scale burning tests are not carried out to support fire hazard assessment. Only the spread of smoke from the kitchen fire to areas outside the unit is commonly studied to calculate the Available Safe Egress Time (ASET) and Required Safe Egress Time (RSET) in the timeline approach. Also, kitchen fires with and without fire resisting walls are not compared. The spread of smoke from the open kitchen to areas outside the residential unit was predicted by fire models. In this paper, the first important parameter on fire hazard assessment, heat release rate for an open kitchen fire will be discussed. The important issues in the estimation of heat release rate will be addressed and discussed. Example calculation of achieving low values of heat release rate will also be illustrated by the principle of superposition. Authority is recommended to review such approach.