The objective of this research programme was to apply commercially available mid infrared fibres and hollow waveguides to the detection of hazardous gases and vapours. The fibres and waveguides operated as optical sensors and provided a means of remote analysis from the point of measurement. The mid infra-red (MIR) methodologies were based on a tunable CO2 laser and a tunable diode laser. To facilitate an evaluation of the sensors, novel calibrated gas and vapour cylinder standards were developed for detection by the sensor prototypes. Trace levels measurement of gases and vapours in the range ppm-ppb using mid infra-red hollow waveguides were shown to be feasible. This approach was applied to ethylene, trichloroethylene, 2-furaldehyde, n-nitrosodiethylamine, and ammonia. Thus, with the hollow waveguide acting as an intrinsic sensor, very small sample volumes gave long interacting optical pathlengths, thereby increasing significantly the speed of response and the level of sensitivity. Silver halide MIR optical fibres coupled to tunable diode lasers demonstrated further that remote measurement of a connectorised gas sampling system is also possible at trace levels over distances of several metres. Signal recovery levels enabled measurement by derivative mode (wavelength amplitude modulation) and also harmonic mode (centre line lock amplitude modulation).