Pressurisation ductwork is a passive fire protection system. It is used to supply a steady stream of fresh air to any area of refuge, designated emergency evacuation or egress route.
Typically, pressurisation ductwork is subject to demonstrable product certification on the basis of fire testing (for example, ISO 6944). In the United States, additional hose-stream testing is required to achieve product certification, as the system includes not just a section of ductwork tested in a full scale floor furnace, but also a firestop, which must survive the hose.
There are two means of providing fire-resistance rated ductwork:
- 1. an inherently fire-resistant duct, or proprietary factory assembled chimney pipes, which tend to be made of sheet metal shells filled with mixtures of rockwool, or ceramic fibre and silicon dioxide
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The use of drywall shaftwall systems has been common for many years. 3-D full scale fire testing (e.g., ISO 6944) resulted in the first certification listing for an inherently fire-resistant duct. Drywall systems were tested as flat walls and a three-dimensional solution surrounding a real duct with four corners was never done. Shaftwall systems are tested to the same standards as all other fire barriers, such as ASTM E119 and ULC S101. These standards mandate thermocoupling in the middle of the test assemblies, in each quadrant and joints. However, no thermocouples go at the interface between the test assemblies and the surrounding structure, which is the closest thing to a corner. Wall Interfaces are in fact fireproofed by the test labs before fire testing, a fact worth consideration in permitting corners in on-site configurations.
