Optical gas sensor technologies can provide important data that can be used to infer the presence of chemical ageing processes that can occur within hermaetically sealed systems. To retain the integrity of these systems, there is a need to develop technologies that enable gas measurements to be taken without effecting chemical equilibria or changing the chemical composition of the system by making the observation (i.e. needs to be non-extractive and non- consuming). Key challenges for this project will be dictated by a number of factors including the need to achieve sensitive and selective gas speciation measurements (for gases including COx, NOx, H2O & O2). In addition due to constraints the sensor technology will need to be chemically and physically compatible with the system in which it is located, the sensor itself be of fibre-size dimensions and to display a long term stability that extends to multiple years.