Risk Category I: The buildings in this risk category group are buildings that exhibit the lowest hazard to life since they have few or no human occupants or are temporary, thus creating considerably less exposure to the hazards of earthquakes, floods, snow and wind than that of a permanent structure. This category includes agricultural facilities, temporary facilities and “minor storage facilities” but the code does not provide an explanation of which storage facilities could be considered minor.
During any discussion of risk categories and the various levels of the different risk categories, it is very important to understand the MEANING of essential facilities and nonessential facilities. The IBC code defines essential facilities as “buildings and other structures that are intended to remain operational in the event of extreme environmental loading from flood, wind, snow or earthquakes”. Nonessential facilities, then, are any buildings that are not classified as essential.
Multiple Use Occupancies: Where a building or structure is occupied by two or more occupancies not included in the same risk category, it shall be assigned the classification of the highest risk category corresponding to the various occupancies. Where buildings or structures have two or more portions that are structurally separated, each portion shall be separately classified. Where a separated portion of a building or structure provides required access to, required egress from or shares life-safety components with another portion having a higher risk category, both portions shall be assigned to the higher risk category.
Section 1604.5 Risk Category. Each building or structure shall be assigned a risk category in accordance with Table 1604.5. Where a reference standard specifies an occupancy category, the risk category shall not be taken as lower than the occupancy category specified therein (IBC Table 1604.5). Where a referenced standard that the assignment of a risk category be in accordance with ASCE 7, Table 1.5-1, Table 1604.5 shall be used in lieu of ASCE 7, Table 1.5-1.
Section 1604.5 Exception: The assignment of buildings and structures to Tsunami Risk Categories III and IV is permitted to be in accordance with Section 6.4 of ASCE 7.
The code and Table 1604.5 establishes special provisions that allow Risk Category IV to include structures that would not otherwise be included in this risk category. Designated emergency shelters and designated emergency response facilities incorporated into secondary schools with certain occupancy loads (275) would typically be considered a Risk Category IV building rather than a category III building.
Facilities supplying emergency backup power for Risk Category IV structures would, themselves, be designated as a Risk Category IV building rather than a Risk Category III facility. Structures with quantities of highly toxic materials in excess of the quantities permitted for a control area in Table 307.1(2), “Occupancy Classification and Use Chapter” would also be designated as a Risk Category IV facility if the conditions comply with Table 307.1(2) criteria in chapter 3 of the IBC code.
