One of the issues associated with disruptions is the generation of large heat loads on plasma facing components, which in future reactor scale devices such as ITER, will severely limit their lifetime through melting and ablation. This thesis concerns measurements of the heat loads during disruptions and relating these to flows of thermal and magnetic energies in the thermal and current quenches on JET. The magnetic energy balance was investigated using Poynting's Theorem to calculate the Ohmic heating of the plasma during the disruption. The Ohmic heating was found to be 78% of the initial self-magnetic energy of the plasma, due to coupling of the plasma to the poloidal field coil circuit and other conductors. 92% of the Ohmic heating was detected as radiation. I conclude there is good magnetic energy balance. The thermal energy losses during disruptions generally take place on a faster timescale than the magnetic energy losses as well as being localised and therefore potentially the most damaging. An infrared camera was used to measure the temperature of the divertor together with image analysis routines developed in this thesis, and the heat fluxes calculated using a heat diffusion equation solver. A wide variation in the thermal energy balance was found with everything from O to 100% of the thermal energy found as heat in the divertor. Disruptions resulting from the collapse of internal transport barriers (1TB disruptions) tend to show very little conduction of thermal energy to the divertor (approximately 5%). However, roughly 50% of the thermal energy was detected as radiation. Evidence for plasma-limiter interaction in the thermal quench of 1TB disruptions is presented as well as an analysis of mechanisms for loss of thermal energy to these areas. Differences in the behaviour of the disruption current spike are also investigated for this disruption class.