An apparatus for manufacturing a three-dimensional object from particulate material, the apparatus comprising: a work space bounded by a floor, a ceiling, a first side wall on a first side of the work space, and a second side wall on a second side of the work space, the first side wall opposing the second side wall; a build bed having a build bed surface, the build bed surface being comprised in the floor of the work space and having a first edge on the first side of the work space, towards the first side wall, and a second edge (160") on the second side of the work space, towards the second side wall; a first gas inlet at or near the first side wall; a second gas inlet at or near the second side wall; a first gas outlet located in the ceiling of the work space, wherein, in a plan view from above the build bed, the position of the first gas outlet is coincident with the first edge of the build bed surface, or is between the first edge of the build bed surface and the first gas inlet; and a second gas outlet located in the ceiling of the work space, wherein, in a plan view from above the build bed, the position of the second gas outlet is coincident with the second edge (160") of the build bed surface, or is between the second edge (160") of the build bed surface and the second gas inlet; wherein the first gas outlet is positioned higher in the work space than the first gas inlet, and the second gas outlet is positioned higher in the work space than the second gas inlet; and wherein the first and second gas outlets (101B, 102B) are couplable to - or wherein the apparatus comprises, coupled to the first and second gas outlets (101B, 102B) - one or more flow devices (210, 211, 212) operable to create first and second gas flows (F1, F2) between the first gas inlet and the first gas outlet, and between the second gas inlet and the second gas outlet, respectively, such as to create respective first and second gas curtains on the first and second sides of the work space in use. a work space bounded by a floor, a ceiling, a first side wall on a first side of the work space, and a second side wall on a second side of the work space, the first side wall opposing the second side wall; a build bed having a build bed surface, the build bed surface being comprised in the floor of the work space and having a first edge on the first side of the work space, towards the first side wall, and a second edge (160") on the second side of the work space, towards the second side wall; a first gas inlet at or near the first side wall; a second gas inlet at or near the second side wall; a first gas outlet located in the ceiling of the work space, wherein, in a plan view from above the build bed, the position of the first gas outlet is coincident with the first edge of the build bed surface, or is between the first edge of the build bed surface and the first gas inlet; and a second gas outlet located in the ceiling of the work space, wherein, in a plan view from above the build bed, the position of the second gas outlet is coincident with the second edge (160") of the build bed surface, or is between the second edge (160") of the build bed surface and the second gas inlet; wherein the first gas outlet is positioned higher in the work space than the first gas inlet, and the second gas outlet is positioned higher in the work space than the second gas inlet; and wherein the first and second gas outlets (101B, 102B) are couplable to - or wherein the apparatus comprises, coupled to the first and second gas outlets (101B, 102B) - one or more flow devices (210, 211, 212) operable to create first and second gas flows (F1, F2) between the first gas inlet and the first gas outlet, and between the second gas inlet and the second gas outlet, respectively, such as to create respective first and second gas curtains on the first and second sides of the work space in use.