move and store material are affected by some limiting factors.  These  factors  are l l l the dimension of the pallet or load to be handled, the dimensions of the MHE to move the pallets, and the   spacing   between   support   columns   and overhead  clearances. In general, utilization of floor area is maximized by minimizing  aisle  spare.  Aisle  space  can  be  minimized by  using  modem  narrow  aisle  storage  equipment  and storing material in depth when possible. An example of  depth-type  storage  are  those  materials  that  are inventoried  in  multiple  pallet  quantities.  See  figure  2-3 for an example of storing material in depth. In this example, the different categories of palletized material in each row are identified by letters. Utilization of Building Clear Height The  term  clear  height  is  often  confusing  when dealing with architects or engineneers. It can mean the height from the floor to the bottom of the roof or to the bottom  of  the  beams.  In  material  handling,  “clear height” means the height under all lighting, heating, and other  overhead  obstructions.  Clear  height  is  the available effective height for storage space that is below all  necessary  clearances.  The  overhead  clearance required below the sprinkler system is at least 18 inches for stacks up to 15 feet. This clearance must be at least 36 inches for stacks higher than 15 feet. All overhead obstructions  must  be  10  inches  above  the  highest equipment  clearance  level. The utilization of clear height is affected by the stackability  of  the  material,  storage  space,  MHE,  and floor-load limit. When pallet racks are used to achieve storage height, the stackability of material is not critical. When using floor stacked bulk storage, the stackability and instability of material directly affect the height of storage. Using storage aids such as pallet frames will permit  load  stacking  and  provide  protection  to  the material. Aisles The preplanning of the aisles in the layout must be done before placing material in storage. Aisle layout is determined by the structure of the building, quantity, nature, and activity of the material to be stored. The aisle should be wide enough for maneuvering the type of MHE to be used. The aisle in bins and shelving areas should  be  wide  enough  for  stock  selector  trucks. Normally, this requires an aisle of 30 to 36 inches in width. The aisles should provide a straight, clear, and unobstructed  passageway.  To  determine  the  width  of the aisles, use the measurement of the turning radius of the MHE. The working aisles are used whenever material is placed into or removed from storage. The two types of working aisles are the transportation aisles and the cross aisles. The transportation aisles run the length of the building. The cross aisles run the width of the building. Depending  on  the  activity  or  operations,  most warehouses  require  two  transportation  aisles.  The aisles should be wide enough to permit two-way traffic for the MHE being used in the area. Personnel aisles are those used as pedestrians routes only  to  provide  access  to  doors  or  other  areas.  Having this type of aisle should be held to a minimum. Use the working  aisles  also  as  pedestrian  routes  if  traffic  and safety  permits. Figure 2-3.-Storing palletized material in depth. 2-5