A cylinder-retaining apparatus (112, 212) for a breathing apparatus (100, 200) comprising: a support frame comprising a cylinder cradle having a single central concave profile and dual laterally spaced concave profiles arranged on either side of the single central concave profile, a first fixing point arranged at a first lateral side of the single central concave profile, a second fixing point (118, 120, 218, 220) arranged at a second opposing lateral side of the single central concave profile, and a third, releasable fixing point on the support frame of a breathing apparatus, the third fixing point being located laterally outside of the first and second fixing points (118, 120, 218, 220) at the first or second lateral side of the single central concave profile and proximate to one of the first and second fixing points (118, 120, 218, 220), and a strap apparatus (116, 216) comprising a strap and a first buckle (126, 226), the strap (116, 216) being secured at a first end to the first fixing point (118, 218) and at a second end the second fixing point (120, 220), the strap apparatus forming a main strap loop (128, 228) for extending around and securing one or more cylinders (106, 206), the strap apparatus (116, 216) being configurable in: i) an expanded configuration in which the main strap loop (128, 228) forms a first effective length for securing a first number of cylinders (106, 206); and ii) a contracted configuration in which a portion of a strap (122, 222) of the strap apparatus (116, 216) is folded to form a secondary strap loop (134, 234), the folded portion of the strap extending through the first buckle, thereby forming the secondary strap loop, and in which the secondary strap loop is secured to the third fixing point (136, 236) such that the main strap loop (128, 228) forms a second effective length shorter than the first effective length for securing a second number of cylinders (106, 206) less than the first number of cylinders (106, 206), and wherein the secondary strap loop (134, 234) is configured to at least partially overlay the main strap loop between the first buckle and the third fixing point, wherein, in the contracted configuration the single concave profile of the cylinder cradle is configured to receive a single cylinder, and in the expanded configuration the dual concave profiles of the cylinder cradle are configured to receive respective first and second cylinders. a support frame comprising a cylinder cradle having a single central concave profile and dual laterally spaced concave profiles arranged on either side of the single central concave profile, a first fixing point arranged at a first lateral side of the single central concave profile, a second fixing point (118, 120, 218, 220) arranged at a second opposing lateral side of the single central concave profile, and a third, releasable fixing point on the support frame of a breathing apparatus, the third fixing point being located laterally outside of the first and second fixing points (118, 120, 218, 220) at the first or second lateral side of the single central concave profile and proximate to one of the first and second fixing points (118, 120, 218, 220), and a strap apparatus (116, 216) comprising a strap and a first buckle (126, 226), the strap (116, 216) being secured at a first end to the first fixing point (118, 218) and at a second end the second fixing point (120, 220), the strap apparatus forming a main strap loop (128, 228) for extending around and securing one or more cylinders (106, 206), the strap apparatus (116, 216) being configurable in: i) an expanded configuration in which the main strap loop (128, 228) forms a first effective length for securing a first number of cylinders (106, 206); and ii) a contracted configuration in which a portion of a strap (122, 222) of the strap apparatus (116, 216) is folded to form a secondary strap loop (134, 234), the folded portion of the strap extending through the first buckle, thereby forming the secondary strap loop, and in which the secondary strap loop is secured to the third fixing point (136, 236) such that the main strap loop (128, 228) forms a second effective length shorter than the first effective length for securing a second number of cylinders (106, 206) less than the first number of cylinders (106, 206), and wherein the secondary strap loop (134, 234) is configured to at least partially overlay the main strap loop between the first buckle and the third fixing point, i) an expanded configuration in which the main strap loop (128, 228) forms a first effective length for securing a first number of cylinders (106, 206); and ii) a contracted configuration in which a portion of a strap (122, 222) of the strap apparatus (116, 216) is folded to form a secondary strap loop (134, 234), the folded portion of the strap extending through the first buckle, thereby forming the secondary strap loop, and in which the secondary strap loop is secured to the third fixing point (136, 236) such that the main strap loop (128, 228) forms a second effective length shorter than the first effective length for securing a second number of cylinders (106, 206) less than the first number of cylinders (106, 206), and wherein the secondary strap loop (134, 234) is configured to at least partially overlay the main strap loop between the first buckle and the third fixing point, wherein, in the contracted configuration the single concave profile of the cylinder cradle is configured to receive a single cylinder, and in the expanded configuration the dual concave profiles of the cylinder cradle are configured to receive respective first and second cylinders.