In-situ measurements of toxic gases in a tube furnace

Infrared Polarization Spectroscopy (IRPS) was used to detect and quantify HCl and HCN in an 800 mm long tube furnace. Pieces of a PVC-carpet or pellets of nylon 6,6 were continuously fed into the furnace producing a heavy smoke. This constitutes a very harsh environment from a diagnostic point of view due to the high smoke density and relatively long length of the furnace. Despite this it was possible to quantify HCl and HCN concentrations in the smoke down to a levels of 50 ppm using IRPS. The explanation for this success is twofold. Firstly the IRPS method is inherently almost noise free due to the use of crossed polarisers, creating a virtually zero background. Secondly the problem with laser beam attenuation due to scattering in the smoke, especially with soot particles, decreases in importance with the fourth power of the laser wavelength. This means that infrared measurements represent a great advantage over measurements in the ultraviolet or visible wavelength range. It is concluded that IRPS shows great promise as a new diagnostics tool in fire technology for small-scale as well as for large scale experiments. Furthermore the in situ nature of the method should be emphasized since this means that valuable information is obtained that can not be extracted from sampling methods such as MS/GC or FTIR for example. This information is important, for example, in egress calculations and analysis of fire chemistry. The method can easily be adapted for other gases such as HF, NO, NO2, HBr, CO and SO2