The video "Class 15 | Pipe schedule Method For Sprinkler System" uploaded by "Irfan CFPS" on YouTube explains the "pipe schedule method," a traditional approach to sizing pipes in sprinkler systems. The method uses tables to determine pipe sizes based on the number of sprinklers and the hazard classification of the building. The video discusses limitations on the use of the pipe schedule method, specifying its use in certain situations, such as renovations or new buildings smaller than a certain size. The video also contrasts the pipe schedule method with hydraulic calculations, which are more precise but more complex, and are used for buildings with higher hazard classifications.