ALLOWABLE AREA AND SEPARATIONS

Cleanroom facilities were often originally constructed as B-2 occupancy (Group B, Division 2, which included office buildings printing plants factories and workshops using materials not highly flammable or combustible, etc.). As such, these facilities were allowed to have unlimited area when sprinklered and surrounded by side yards. When such facilities are converted to Group H occupancy, severe restrictions on the allowable area may be imposed by the UBC. 

The maximum allowable area must be evaluated based upon the correct occupancy and constmction type in conjunction with UBC Table 5-B and UBC Sections 504 and 505. The areas specified in Table No. 5-B and UBC Section 504.2 may be tripled in one-story buildings and doubled in buildings of more than one story if the building is provided with an approved automatic sprinkler system throughout. The basic allowable area may be doubled for multiple story buildings and may be increased for side yards (accessible to the fire department) where they exceed 20 feet. 

Many cleanrooms and wafer fabrication ( fab ) occupancies have basements used for the support of their operations. If the lowest level is not considered a first-story (see definitions in UBC Section 203 and 220), then it does not enter into the ealculation of allowable area, regardless of its occupancy. 

The limitations in the UBC and UFC on allowable quantities of HPMs in a given oeeupancy must be evaluated in concert with the area test. Speeifieally for a semiconductor facility, UFC Table 5103-A defines the maximum qroatwfttyofHPMs allowed per fab area, stipulating density limits in lb./SF, gal./SF or CF/SF. In the event an existing fabrication area exceeds these quantities, it must be divided into multiple fabs, or the inventory must be redueed. 

Division of an existing structure into separate buildings (if required to comply with the maximum allowable area limitations) may be accomplished by die construction of area separation walls (UBC Section 504.6). (See Fig. 2.) 

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