Designers

Performance Criteria

The Building Regulations (2000) Approved Document B gives detailed guidance on fire safety. This document sets out time periods for stability, integrity and insulation for various compartment walls and floors in a building.
The design of Fire Resistant Ductwork of all types is described in BS9999 this document requires the ductwork to be tested in accordance with BS476 Part24: 1987 BS476 Part24: 1987 describes the method for testing ductwork to establish time periods for stability, integrity and insulation. The testing covers the types of fire exposure, Duct A (Fire Outside) and Duct B (Fire Inside).

Designers determine the fire rating to BS476 Part 24 and the required time periods for:

• Stability
• Integrity
• Insulation

Stability

The ability of a duct and the support system to remain intact and fulfil their intended function for a specified period of time.

Integrity

The ability of a duct to remain free from cracks, holes or openings outside the compartment in which the fire is present for a specified period of time.

Insulation

To ability of a duct to maintain its separate function without developing temperature on its external surface, outside the compartment in which the fire is present, and to stop radiant heat from igniting secondary services, igniting materials stored with a low ignition points or preventing pedestrian escape of the building through defined compartments.

It is essential that the whole system is considered, including ductwork, fittings, supports, access doors, attenuators, etc.
All fire-rated ductwork supports are calculated, designed and tested in consideration of a fully developed fire as described in the ISO834:1975 (E) fire resistance test standard time - temperature curve.