The JET machine and associated facilities require significant maintenance and enhancement installation activities in support of the experimental exploitation programme. A proportion of these activities are within radiological and respiratory hazardous environments. As such, breathing air-fed one piece pressurised suits provide workers with protection from the inhalation of both airborne tritium and beryllium dust. The design of these suits has essentially developed empirically. There is a practical necessity to improve the design to optimise worker performance, protection and thermal comfort. This paper details the complexity of modeling the three dimensional thermofluid domain between the inner surface of the suit and under garments that includes mass as well as heat transfer, suiting geometry, human metabolism and respiration and effects of limb movements. The methods used include Computational Fluid Dynamics (CFD), theoretical adaptations of mixed-phase turbulent flow, profile scanning of a suit and actuating life size mannequin and data processing of the images and experimental validation trials. The achievements of the current programme and collaborations are presented in the paper and future endeavors are discussed.