Part of the Thor Duct ® service for licensed manufacturers, is that we will engage with consultant engineers on any technical issues relating to the fire and smoke ductwork. Here are some of the most frequently asked questions that we get asked by M&E Contractors, installers and fire authorities about smoke extract, flashover, thermal insulation, and fire dampers.
Q. Is smoke extract in multi-compartments always insulated?
The process of mechanically removing smoke from the scene of a fire, gives rise to a potential risk called flashover, or in technical terms, thermal radiation feedback. Heat is energy, and at flashover temperatures, the contents and gasses in a room may spontaneously combust due to the temperatures.
The tests for smoke extract ductwork multi-compartment is EN 1366-8. During the test, the ductwork is insulated, but the results are derived from the EN 1366-1 fire tests.
By insulating the smoke extract ducts and transporting the hot gases from the scene of a fire to the atmosphere, we limit the risk and prevent flashovers. The last thing a fire crew need to encounter are secondary fires, as a result of our efforts to remove gases from the scene of the initial fire.
Smoke ducts in a multi-compartment design will be insulated. Where we construct a dedicated fire shaft, the ductwork in the shaft may be uninsulated. The insulation protection is provided by the shaft construction. The shaft must be constructed for the smoke duct only. No other services may be in the shaft.
Q: Is smoke extract in multi-compartments always insulated?
Thermal insulation has properties similar to fire insulation, but may not have been tested in an EN 1366-1 fire test. The question you need to always ask:
Has the insulation been tested with the ductwork?
It’s a system, and a classification report to EN 13501-4 will specify the ductwork and insulation. Thermal insulation is not a fire insulation. A smoke extract ductwork is an emergency system, and fire insulation will be able to handle the exhaust temperatures, having been proven in a fire test.
Q: Does smoke extract ductwork need to be insulated on the roof?
Insulation is used to prevent flashover as hot gases pass through fire compartments.
On the roof, the smoke extract ductwork is at atmosphere, and the flashover risk no longer exists. We would not normally insulate the smoke duct on the roof. There may be requests to do so because of the proximity of services and roof mounted equipment. In these instances, the insulation needs to be protected from the elements.
Q: What is the difference between EN 1366-8 and EN 1366-9?
Both tests are smoke extract tests, but tests for different applications.
BS EN 1366-9 is a duct suitable for smoke extract in single fire compartments. It exhausts hot gases into the atmosphere without entering another fire compartment. The test for EN 1366-9 is conducted without insulation and at 600 °C. Insulation is not relevant for single compartments. The duct is exposed to lower temperatures and can radiate heat during the test. The stresses are less than an EN 1366-8 test.
EN 1366-8 ductwork are tested at full hydrocarbon fire temperatures, and are subject to insulation, which creates significant stresses on the duct as it tries to maintain 90% cross sectional area. This duct is tested for multi-compartment applications.
Higher temperatures and insulation are the significant differences between the two.
Q: Are EN 1366-2 Fire Dampers suitable for EN 1366-8 smoke ducts?
Fire dampers are tested to EN 1366-2.
Smoke dampers are tested to EN 1366-10.
A fire damper contains a fusible link, which reacts when a temperature rise occurs. 72²C is the normal fusible link temperature. The link causes the damper to close, thus maintaining the integrity of the structure it is installed in, to the prescribed time in minutes.
Fire dampers should never be included in a smoke extract duct.
This is because ducts are designed to carry the hot gases from the scene of the fire out into the atmosphere. A fire damper will close and this would prevent the smoke from being exhausted safely.
The correct damper to include in your design is a smoke damper tested to EN 1366-10.
In the event of a fire, the damper will open or close, depending upon the fire location. The damper will close where there is no fire, and open to allow the gases to be exhausted from the scene of the fire. Controls are clearly very important. EN 1366-10 smoke dampers are suitable for EN 1366-8 smoke ducts. They are tested for leakage to the same scrutiny as smoke ducts, and to the same flow rates during the test. They are classified to EN 13501-4.
Michael is an expert in fire rated ductwork
For any further questions or to ask about a CPD presentation please contact Michael Renaghan, Technical Lead at Thor Duct ®.