The behaviour of fire within a deep (high depth to height ratio) enclosure with various openings in one end has been studied experimentally and by simulation (using FDS4). Sixteen fuel-trays were placed within an 8.0 m long x 2.0 m wide x 0.6 m high steel enclosure. The experiments confirmed previous smaller scale experiments, showed that the fires in deep enclosures are strongly influenced by the ventilation and are not at all uniform through the depth of the enclosure. The severity of exposure of structural members is much more severe near the ceiling near the front of the enclosure compared with the back of the enclosure. Depending on the criterion used the severity at the front may be from twice to five times as severe as at the back of the enclosure. The movement of the flame-front in the FDS4 simulation is similar to that found experimentally, but the predicted timing of flame-front movement and predicted HRR varies considerably from the experimental values.