Flexible polyurethane in fire investigation : detection of hydrogen cyanide and time until flashover
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Although the majority of fires attended by Fire and Rescue NSW (FRNSW) originate in the kitchen, most fatalities occur in the lounge and bedrooms. These rooms have a comparatively higher proportion of polyurethane (PU) and hence this project sought to focus on the role of PU during the progression of a fire. The research presented here is a significant addition to the existing body of knowledge and, for the first time, investigates whether the time until flashover is proportional to the amount of PU in a cell. Additional research was undertaken to determine the lowest temperature that hydrogen cyanide (HCN) could be detected in effluent produced from the degradation of polymeric materials, specifically flexible PU. Thirty large scale burns, which were fuelled with PU-containing furniture, were conducted at three different sites in the United States of America (USA) and Australia between 2007 and 2010. After significant method optimisation (that concentrated on the standardisation of the majority of the experimental parameters) the time until flashover based on the amount of PU in the cell was successfully determined. Gas analysis was run in parallel to the large scale burns. To facilitate gas sampling an apparatus was developed to remotely trap effluent produced during the progression of a fire, by drawing it through potassium hydroxide (KOH) solution from directly inside the fire cell. The system was used in conjunction with a novel HCN detection method using Ultraviolet Visible (UV-Vis) spectroscopy. The method involved adding nickel (Ni²⁺) solution to the KOH + fire effluent solution and analysing the resultant solution using UV-Vis spectroscopy. The positive presence of HCN in the fire effluent could be shown by the presence of the tetracyanonickelate (II) complex with a characteristic absorbance at 267 nm. The presence of HCN in fire effluent was quantitatively determined in the pre-flame and at an interval of 30 minutes post suppression in the large scale burns conducted in Australia. In addition a commercially available Ion Selective Electrode (ISE) specific to HCN was used to analyse the KOH + fire effluent solution; though it and was found that this technique was best suited to qualitative, rather than qualitative, work. In a controlled laboratory environment the detection of HCN between 171 °C – 203 °C was investigated. Using a modified version of the method used to detect HCN at the large scale test burns, PU foam was heated in an oven between 171 °C – 180 °C and 184 °C – 203 °C and the resultant effluent was drawn through KOH solution at different time intervals. An amount of Ni²⁺ solution was added to each of the collected sample solutions. The presence of the characteristic absorbance caused by the combination of CN⁻ and Ni²⁺ to form tetracyanonickelate (II) complex was determined using UV-Vis spectroscopy. In some cases the fire effluent was found to contain HCN after heating PU foam for 30 minutes and 50 minutes at both temperature ranges. The data presented in this body will provide insight to fire investigators when determining the origin and cause of fires, when flashover is suspected to have occurred. This research will certainly benefit the occupant as it provides data to inform the development of a self egress plan that acknowledges the presence of PU in a fire, and its potential hazards. Emergency services members can use the information described in this work to further inform the level of respiratory personal protection equipment (PPE) required when they attend the post suppression scene of a PU fuelled fire. Finally, the research undertaken in this work regarding time until flashover has the potential to inform fire brigades, such as FRNSW, at a strategic level when developing their response time isochrome map (the time taken for an engine to respond to a fire at the furthest point within their area.
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