A method of generating combustion by means of a burner assembly comprising a refractory block, a fuel supply system and an oxidant supply system, the refractory block defining along a first plane at least one fuel passageway (28A, 28B, 28C) extending from a fuel inlet port to a fuel outlet port, and substantially along a second plane at least one oxidant passageway (42A, 42B) extending from an oxidant inlet port to an oxidant outlet port (46A, 46B), said first and second planes intersecting along a line that is beyond said outlet ports, said oxidant supply system comprises an inner oxidant supply means having an inlet connected to a source of a first oxidant and an outer oxidant supply means which at least partially surrounds the inner oxidant supply means and which has an inlet connected to a source of a second oxidant, said inner oxidant supply means extending at least partially into the at least one oxidant passageway, the method including: (a) selectively supplying the inner oxidant supply means of an oxidant passageway (42A, 42B) of a refractory block with a first oxidant, said first oxidant advantageously containing at least 70% vol. of oxygen and preferably at least 90% vol. and more preferably at least 95% vol.; (b) selectively supplying the concentric outer oxidant supply means of the same oxidant passageway with a second oxidant, said second oxidant preferably containing less than 25% oxygen, and being advantageously in the form of air; and (d) directing said oxidant or oxidants towards a fuel for combustion therewith downstream of the burner assembly; the method being characterized: • in that the outer oxidant supply means extends at least partially into the at least one oxidant passageway; and • in that the oxidant supply system is configured to supply to the outlet port of said at least one oxidant passageway either just one of said first and second oxidants or a combination of both; the method further including: (c) varying the ratio between said first and second oxidants being supplied to the at least one oxidant passageway between supplying only the first oxidant to the inner oxidant supply means, supplying only the second oxidant to the concentric outer oxidant supply means and supplying a combination of the first oxidant to the inner oxidant supply means and of the second oxidant to the concentric outer oxidant supply means. (a) selectively supplying the inner oxidant supply means of an oxidant passageway (42A, 42B) of a refractory block with a first oxidant, said first oxidant advantageously containing at least 70% vol. of oxygen and preferably at least 90% vol. and more preferably at least 95% vol.; (b) selectively supplying the concentric outer oxidant supply means of the same oxidant passageway with a second oxidant, said second oxidant preferably containing less than 25% oxygen, and being advantageously in the form of air; and (d) directing said oxidant or oxidants towards a fuel for combustion therewith downstream of the burner assembly; • in that the outer oxidant supply means extends at least partially into the at least one oxidant passageway; and • in that the oxidant supply system is configured to supply to the outlet port of said at least one oxidant passageway either just one of said first and second oxidants or a combination of both; (c) varying the ratio between said first and second oxidants being supplied to the at least one oxidant passageway between supplying only the first oxidant to the inner oxidant supply means, supplying only the second oxidant to the concentric outer oxidant supply means and supplying a combination of the first oxidant to the inner oxidant supply means and of the second oxidant to the concentric outer oxidant supply means.