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Fire protection of ducts

Ducts sometimes pass through areas where the fire is active before reaching protected areas.

Applications

ventilation ducts

In the event of a fire, the ventilation ducts ensure the supply of fresh air and the pressurisation of neighbouring rooms.
These ducts sometimes pass through the areas where the fire is active before reaching the protected areas.
It is therefore essential to ensure that ventilation ducts meet the following properties whether the fire is outside the duct (normal operation) or inside (in cases where the duct has been degraded):

• Fireproofing, so that the fire does not spread from one room to another
• Thermal insulation to limit the temperature rise.
• Limited deformation and mechanical strength of the conduit and its support system to perform its function for the intended duration.
• Smoke-tight (optional), to limit the spread of asphyxiating gases.
To do this, EN 1366-1 gives two types of tests:
• The "duct A" test: the fire is outside the duct, which is kept under vacuum. This test mainly measures the fire and smoke tightness of the duct, but also the thermal insulation, as well as its mechanical resistance in case of external fire.
• The "duct B" test: the fire is outside and inside the duct where an air flow is provided by a fan, the temperature measurements are made outside the furnace. This test mainly allows to measure the thermal insulation of the duct walls when the fire is inside, but also its behaviour in "degraded" operation; moreover, the fan at the outlet of the duct is regularly stopped in order to simulate a breakdown.

the ventilation ducts ensure the supply of fresh air and the pressurisation of neighbouring rooms.

smoke extraction ducts

The role of smoke extraction ducts is to extract hot, stale air, in order to limit the rise in temperature in the premises and facilitate the intervention of emergency teams. In addition to the properties of ventilation ducts, smoke extraction ducts must therefore have the following properties:
• Mechanical resistance when the fire is inside and outside the duct.
• Tightness when the fire is only inside the duct and the duct is depressurised. This is necessary to ensure that the gases drawn in are the smoke and hot gases from the fire and not the clean ambient air that has filtered through the leaking duct.

In order to justify this performance, the ducts are tested according to EN 1366-8 which requires that the ducts have been successfully tested:

• According to EN 1366-1 (A and B ducts)
• With the additional test called "duct C": the fire is outside and inside the duct. A fan extracts the hot air from the oven and a perforated grid is placed between the part of the duct in the oven and the part outside; this creates a vacuum in the outside part. This test verifies the mechanical strength of the duct when subjected to fire inside and outside, and verifies with oxygen probes that the air in the outer part of the duct comes from the furnace area and not from outside through leaks in the duct.

The role of smoke extraction ducts is to extract hot, stale air, in order to limit the rise in temperature

Fire resistance classification of ducts

Following these tests, the performance of the ventilation or smoke extraction ducts is expressed by the following classifications:

• E: flame and hot gas tightness
• I: thermal insulation: temperature rise on the non-fire side less than 140 °C on average and 180 °C at any point
• S: Smoke-tightness, optional
• ho and/or ve: depending on the configuration in which they were tested (horizontal or vertical)
• o→ i, o ←i or o ↔i : only for ventilation ducts depending on whether they have been tested with an external fire (duct A, classification o→ i) or an internal fire (duct B, classification o← i) or both (classification o↔i). The decree of 22nd March 2004, as amended, requires that the ventilation ducts used in buildings be validated by tests in both external
and internal fires. All ventilation ducts treated with FIRESPRAY^® have obtained these two classifications and therefore justify a classification o ↔i.
• Multi: only for smoke extraction ducts, indicates that they can be used to extract smoke in multi-compartment areas
• Operating pressure: only for smoke extraction ducts, indicates the maximum permissible cold vacuum or overpressure.