Please note: All interim revisions for this edition available at time of your purchase will be included. Thermoplastic Sprinkler Pipe and Fittings for Fire Protection Service UL 1821 1 Scope 1.1 These requirements cover thermoplastic pipe and fittings for use in wet pipe sprinkler systems for fire protection service. 1.2 Thermoplastic pipe and fittings covered by these requirements are intended for use in sprinkler systems in any of the following types of occupancies: a) Light hazard occupancies as defined in the Standard for Installation of Sprinkler Systems, NFPA 13; b) Residential occupancies as defined in the Standard for Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, NFPA 13D; and c) Residential occupancies as defined in the Standard for Installation of Sprinkler Systems in Low-Rise Residential Occupancies, NFPA 13R. 1.3 The pipe and fittings covered by these requirements are intended to be installed in accordance with the Standard for Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes, NFPA 13D; the Standard for Sprinkler Systems in Low-Rise Residential Occupancies, NFPA 13R; or the Standard for Installation of Sprinkler Systems, NFPA 13.