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 are couplable to - or wherein the apparatus comprises, coupled to the first and second gas outlets - one or more flow devices 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 are couplable to - or wherein the apparatus comprises, coupled to the first and second gas outlets - one or more flow devices 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. <EOS>