NFPA 557-2020 Standard for Determination of Fire Loads for Use in Structural Fire Protection Design.
5.1 Types of Fire Loads. Fire loads shall be calculated as both localized fre loads and distributed fre loads. 5.1.1* Prior to a change of use or occupancy, renovation, or modifcation, the building owner shall be responsible for the evaluation of the new fre load. 5.1.2 If there is a change of use or occupancy, and the fre load in the new use or occupancy exceeds the fre load that was originally developed, then the fre resistance of the building shall be analyzed to evaluate if the existing passive fre protec‐ tion meets the design objectives for the new use or occupancy. 5.2 Defning the Compartment. 5.2.1 The compartment shall be selected as either the entire building or that portion of the building that is bounded by exterior surfaces of the building and by fre-rated boundaries that are capable of containing a fre for the entire duration through burnout. 5.2.2 For areas where there are no fre-rated boundaries, the entire building shall be selected. 5.3 Distributed Fire Loads. 5.3.1 Distributed fre loads shall be determined to refect the total fre load throughout a compartment.
5.3.2 Distributed fre loads shall be determined in accordance with Chapter 6 or Chapter 7. 5.4 Localized Fire Loads. 5.4.1 Localized fre loads shall be determined to refect concentrations of combustible material that have the potential to pose a more severe thermal exposure than the thermal expo‐ sure that would result from the uniform fre load. 5.4.2* Combustible materials shall be considered concentra‐ ted whenever the mass per unit area of one or more items is a factor of 2.57 greater than the established distributed fre load. 5.4.3 Localized fre loads shall be determined based upon surveys as described in Chapter 7 or upon architectural design data. 5.4.4 The localized fre load determined in accordance with this section shall be subject to the approval of the authority having jurisdiction (AHJ). 5.4.5 Localized fre loads shall be reported by location in the building and shall include the expected value and a measure of the variability of the value (mean and standard deviation).NFPA 557 pdf download.