Spray-applied Fire Resistive Materials (SFRM) . . . SFRM are classified into 3 main categories with a fourth category being a catchall for anything not included in the previous three.
Commercial Density Materials: (minimum 15 pcf): Commonly used throughout the United States for interior and concealed applications. Typically, an office building where concealment will be provided with sheetrock and/or acoustic tiled ceilings.
Medium Density Materials: (minimum 22 pcf): Designed for use in interior, but exposed applications where there might be a concern for physical damage. Mechanical rooms with exposed fireproofing would be an excellent example of the proper usage of a medium density fire resistant material.
High Density Materials: (minimum 39 pcf): High-density materials have experienced limited use in the Northeast. It is designed for exterior applications such as parking garages, natoriums, carports, etc. This classification of materials are recommended for use anywhere where weather, water, or physical abuse might become an issue.
Special Fireproofings: This classification of fire resistant materials include various types of materials such as board systems, intumescent systems, and a slew of other systems and materials. Each tend to service niche applications created by the environment, design, physical limitations, or some other unique condition. These materials vary widely in their application, properties, application requirements, and cost.