Fire Rated Ductwork
Fire Resisting Ventilation Duct (image 1)
A duct or ductwork system used for the distribution, or extraction of air, designed and tested to satisfy the criteria of test defined in British Standard BS476 part 24:1987 (ISO 6944:1985), (Duct Type A & Duct Type B).
Smoke Extract/Outlet Duct
A duct or ductwork system used for the extraction of products of combustion, designed and tested to satisfy the criteria of test defined in British Standard BS476 part 24:1987 (ISO 6944:1985), (Duct Type B). Additionally this duct must prove by test that within the fire compartment, its cross sectional area is maintained above 75% when subjected to the full fire temperature.
Kitchen Extract Duct (image 2)
A duct or ductwork system that is entirely independent of any other duct or ductwork system within a building, which serves as an extract for non-domestic kitchens (BS5588 part 9:1999 clause 6.4.6.2 refers). Designed and tested to satisfy the criteria of test defined in British Standard BS476 part 24:1987 (ISO 6944:1985), (Duct Type A & Duct Type B).
Note; Testing of both types A & B are equally important, as due to the likelihood of combustible deposits within the duct it is necessary to protect both the duct and the adjacent compartment from ignition due to radiated heat. In accordance with BS 476 Part 24 : 1987 the fire resistance of ventilation ductwork shall be expressed in minutes of duration of heating in accordance with the ISO 834 : 1985 (Cellulosic - Standard Time/Temperature Curve) until failure occurs to one or more of the following criteria –
Stability / Integrity / Insulation Stability (image 3)
Stability failure shall be deemed to have occurred in duct A within the furnace and in ducts A and B outside the furnace when the duct no longer fulfils its intended function. (For smoke outlet ducts stability failure will also be deemed to have occurred when there is any restriction of the cross sectional area of the duct to 75% or less of its original area)
Integrity
The presence and formation of any cracks, holes or other openings outside the furnace through which flames or hot gases can pass. Insulation (image 4) Insulation failure shall be deemed to have occurred when the temperature rise above initial ambient on the unexposed surface of the duct outside the furnace exceeds either:
• 140 °C as an average value above ambient.
or
• 180 °C as a maximum value above ambient. For a Kitchen extract duct (Type A) these temperature limits also apply to the inside surface of the duct within the furnace. In addition to testing to BS476 Part 24, further independent furnace testing has been carried out in accordance with BS 7346 to simulate smoke extract temperatures of between 250 °C and 600 °C. The results allow us to tailor the insulation requirement for smoke extract systems where the gas/fume temperature is known.
