Fire resistant insulation and sheeting of metal air ducts

2.9.1 Fire resistant insulation of circular air ducts

If fire resistance is required for the air duct, it is recommended to use systems tested according to EN 1366.1 Circular ducts can be insulated against fire using mineral wool mesh blankets. There are two products on the market which satisfy the requirements for fire resistance:

non-combustible rock wool mesh blanket;
lightweight mineral wool mesh blanket.

These are products for fire separating systems ranging from 15 to 120 minutes, depending on density and/or insulation thickness. An increase in the weight of the duct in relation to the duct suspension must be taken into account. The weight per m2 of sheet surface is a measure for this.
For a 60 minutes fire resistant system the following products are available:

2.9.2 Fire resistant insulation of rectangular air ducts

If the air duct has to meet fire resistance requirements, it is recommended that systems tested to EN 1366-1 are used. Rectangular ducts can be insulated with mineral wool or fibresilicate sheets.

2.9.2.1 Mineral wool insulation sheets

There are two mineral wool products on the market for the fireproof insulation of rectangular ducts:

non-combustible rock wool sheet;
lightweight mineral wool sheet.

The mineral wool sheets are fitted directly to the air duct in accordance with the supplier's instructions. These sheets are usually fixed using weld pins or screw spacers. Sometimes it is also necessary to fix the sheets to each other using a special type of glue.
The products can be used for fire separating systems ranging from 15 to 120 minutes, depending on density, insulation thickness and/or duct orientation. An increase in the weight of the duct in relation to the duct suspension must be taken into account. The weight per m² of sheet surface is a measure for this.

For a 60 minute fire resistant system, the following options are available in mineral wool boards:

2.9.2.2 Insulating sheets of fibresilicate

non-combustible sheets of fibresilicate.

Asbestos-free sheets made of fibres, Portland cement and aggregates should be installed according to manufacturer's instructions.

2.9.3 Suspension of fire resistant insulated air ducts.

The air ducts should in principle be suspended as in the standard test method.
The data below is taken from publication SBR/ISSO 809.14.
Table 26 - Details of the studs

As a rule of thumb, we recommend this:
Maximum distance between two suspension points (c.t.c.): 1.5 with the first suspension point at maximum 0.5 m from the fire damper. Weight per suspension point maximum 50 kg.
Suspensions must be supported by means of a mounting rail and must be suspended by means of threaded rods at least M6 in metal plugs. This applies to both rectangular and circular ducts.