An incident recently occurred on a PDO well pulling hoist. The well cellar collapsed under the strain applied by the hoist mast base beam resulting in the hoist mast to drop 1 meter. The well and mast were immediately secured. It was found that the well cellar had collapsed on the side where the hoist beam was resting on the soil. This allowed the stool pad which sits between the hoist mast carrier jacking mechanism and the base beam to tumble and to drop the mast 1 meter.