It is possible that the drawing is using the nomenclature from ISO 4063 (EN 24063) which indicates the welding method by using a three digit number. For example, MIG welding (GMAW with inert gas) is indicated by 131. TIG welding (GTAW) is indicated by 141. Firecracker welding is the method indicated by 118. I am not familiar with this term, but it appears under the broader category of Metal-arc welding without gas protection. Maybe someone else can provide additional details.