Pressurisation ductwork

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Pressurisation ductwork made of Durasteel.

Pressurisation ductwork is a passive fire protection system. It is used to supply a steady stream of fresh air to any area of refuge or designated emergency evacuation or egress route.

Purpose

• To ensure a positive pressure environment of clean outside air, free from smoke to enable people to either hold out until rescued or to escape with a minimum of dangerous smoke exposure.

Requirements

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.

Pressurisation systems are evaluated for exterior fire exposure. Grease ducts, on the other hand, are evaluated for both interior and exterior fire exposures.

Systems

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

or

• 2. ordinary ductwork equipped with exterior fireproofing materials, such as blanket rockwool, ceramic fibre or intumescent paint.

History

Grandfathering

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Successful shaftwall test to ASTM E119, ULC-S101 or NFPA 251 with corner fireproofing.

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.

In Europe, where ISO 6944 originated, rockwool systems, calcium silicate and sodium silicate bound and pressed vermiculite as well as the proprietary Durasteel systems, have been in use for decades .

See also

• Heat and smoke vent
• Fire protection
• Passive fire protection
• Duct (HVAC)
• Smoke exhaust ductwork
• Grease duct
• Emergency evacuation
• Area of refuge
• Fireproofing
• Firestop
• Underwriters Laboratories

External links

• ISO 6944-1:2008 Fire containment -- Elements of building construction -- Part 1: Ventilation ducts
• UL treatise on "Wrapping Systems"
• Recommended IFC Guidelines For Evaluating Engineering Judgments on Fire Resistant Duct Enclosure Systems for Ventilation Ducts