It is also used in some intumescent systems. There are mainly two types of PFP&colon; intumescent fire protection and vermiculite fire protection. The thickness of this intumescent coating is dependent on the steel section used. Air transfer fire dampers are passive such as intumescent types or mechanical types. Also, intumescent fire dampers can be qualified to ASTM E2912. Intumescent coatings for steel constructions must be approved in standardized fire tests. The intumescent resins in batt-based firestop pillows contains hydrates, or chemically bound water.