Shelf Storage 1 : Storage on structures less than 30 in. (76. 2 cm) deep with shelves usually 2 ft (0. 6 m) apart vertically and separated by approximately 30-in. (76. 2-cm) aisles
NFPA 230 Standard for the Fire Protection of Storage 1999 ed. http://www.nfpa.org/assets/files/aboutthecodes/230 /230-f2002-rop.pdf, (Std: Fr Prac of Storage - Amer) {267 NFC}