HCN yields and fate of fuel nitrogen for materials under different combustion conditions in the ISO 19700 tube furnace and large -scale fires

Abstract

For calculations of time-concentration curves for toxic products in full-scale fires it is necessary to know how the yields of key toxic species vary with combustion conditions and fuel composition. In this paper, the relationships between equivalence ratio (phi) and HCN yields and conversion efficiencies (mass fraction of fuel nitrogen released as HCN) are presented for ten common nitrogen-containing materials and products combusted in the ISO19700 tube furnace under steady flaming conditions at a furnace temperature of 650-700°C in air. Additional experiments were carried out at 850°C and also in 10% and 12% oxygen. Large-scale fire tests were carried out under well-ventilated and vitiated combustion conditions on three materials for comparison. For non-FR materials sigmoid relationships between phi and HCN yields were found with very low yields (0.00003-0.002 g/g) at phi 0.5 increasing to a wide range (0.0036 g/g to 0.11 g/g) at phi 2 depending upon the material. Yields from some materials were also found to be sensitive to furnace temperature and oxygen concentration. When normalised for nitrogen content, the relationships between phi and HCN recovery were more similar, falling into high (maximum HCN recovery fraction ~ 0.16) and low groups (maximum 0.085). Although the large-scale test data were more variable, a good agreement was found with the tube-furnace results.

Development of a Risk Assessment Method for Life Safety in Case of Fire in Rail Tunnels

“…E.g., training of staff and guidance during evacuation circumstances can have significant impact [21] by reducing pre-movement and evacuation time. -Fire growth: the fire growth curve is of great importance when assessing life safety, due to the relation of the growing fire with the release of heat and toxic products of combustion [22]. With these factors, representative scenarios are determined to be taken into account in the bow-tie.…”

“…HCN can only be created if nitrogen is present in the fuel. According to [22] the HCN yield is related to the equivalence ratio, but there is strong spreading in the data due to material dependency. Consequently, it is advised to determine the materials which are likely to burn in case of fire in a rail car.…”

In situ Measurements of HCN in a Tube Furnace with Infrared Polarization Spectroscopy

“…1. The geometry and operation are similar to the steady state tube furnace standardized test [6,7]. The length of the furnace was 800 mm.…”

“…Under typical fire conditions HCN can be consumed by isomerization to HNC, or by oxidation reactions with radicals, mainly O and OH [2]. Investigations using the steady state tube furnace [6,7] using nylon 6,6 show that for well ventilated combustion most HCN ends up as NO x [8], with NO 2 as the most important toxicant, whereas for equivalence ratios equal to or greater than one HCN is the most important toxicant produced [9].…”

“…Typical experiments in the steady state tube furnace give total yield information for different gases, for different fuels, and for different operating conditions once the fire effluents have left the furnace [6,7,[10][11][12]. However, in order to understand the kinetics behind the total yield of a toxicant, including pyrolysis as well as both production and consumption in the gas phase, in situ measurements are necessary.…”