Those conditions that apply to the rigorous, harsh, and unique applications of fire apparatus, including but not limited to local operating and driving conditions, frequency of use, and manufacturer's severe service (duty) parameters
NFPA 1911 Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus, 2007 ed. https://www.iafc.org/files/1EVM/evms_NFPA1911_1071 andEVT.pdf, (Std: Insp, Maint, Tst and Retirement of In-Srvc Automotive Fr Aptus - Amer) {415 NFC}