In-rack fire protection sprinkler system

A method of providing fire protection for commodities including Class I-IV hazards, Group A cartoned and exposed plastics (expanded and unexpanded), flammable liquids, tires, roll paper, and aerosols, stored in a plurality of adjoining racks that have a vertical flue space provided between a set of two adjoining racks, of the plurality of adjoining racks, the method comprising:

• (A) providing a fluid supply conduit configured to deliver a fire protection fluid received from a fire protection fluid source;
• (B) providing at least one solid horizontal barrier that covers (i) a rack, of the two adjoining racks, (ii) another rack, of the two adjoining racks, that is adjacent to the rack, and (iii) the vertical flue space between the rack and the other rack, the at least one solid horizontal barrier being provided at a predetermined height, and having a width that is at least equal to a width of the rack, and a depth that is at least equal to a sum of (i) a depth of the rack and (ii) a depth of the vertical flue space, and the at least one solid horizontal barrier being formed as a singular piece of a solid material;
• and
• (C) providing at least one rack-level fire protection sprinkler, the at least one rack-level fire protection sprinkler (i) being connected to the fluid supply conduit, (ii) being disposed in the vertical flue space below the at least one solid horizontal barrier, (iii) having a K-factor of 11.2 gpm/(psi)1/2 or greater, and (iv) being vertically spaced from the commodities stored on the rack and the other rack covered by the solid horizontal barrier.