Numerical simulations for fluid flow and heat transfer in horizontal air spaces between shim stock and a test sensor are carried out as part of a study of the performance of thermal protective garments during an exposure to fire. The Navier-Stokes and energy equations are solved simultaneously using an in-house code. The radiation modelling is carried out using the finite volume method. The bottom boundary of the enclosure is treated as a series of isothermal rectangular elements with known temperatures that are measured experimentally. The temporal increase of temperature of the sensor which is centrally located at the upper boundary is calculated with the lumped capacitance method. The simulated temperature of the sensor is compared with the experimental data and good agreement is found for smaller air. gaps. Flow streamlines are presented and compared with experimental flow visualization pictures. Results of convective and radiative heat fluxes are presented and compared for different air gaps. (C) 2009 Elsevier Ltd. All rights reserved.