The present invention relates to a ventilation system and is concerned with a ventilation duct which permits the passage of the ventilation duct through a fire com¬ partment-limit, for instance through a wall, a floor, a ceiling or another structural part of a fire compartment building.

By fire compartment is meant a part of a building which is separate from the remainder of the building so as to correspond to a given fire resistance grade, which is determined by the nature of the building concerned and the number of stories or floors that it contains. A fire compartment may include for instance a room, a stair well, a boiler room, or group of connected rooms, for instance a group of apartments or offices. The main principle is that activities which are not immediately related to one another shall include different fire com¬ partments and that each fire compartment shall be de¬ fined by building structures that prevent the spreading of fire and fire fumes. A similar level of ambition applies to air treatment plant installed within such a building. One of the most difficult areas of fire protection planning is that of determining safety precautions which will prevent fire and fumes from spreading through ventilation systems. Fire can spread in different ways through a ventilation system. For instance, fire can spread as a result of direct contact between solid or loose combustible mate¬ rial and the flames of a fire, as a result of direct contact with hot metal objects, or as a result of the heat radiated by metal objects, or as a result of being heated to an ignition temperature by the hot fire gases. In order to prevent fire from spreading through a venti¬ lation system, ventilation ducts are either insulated against fire or it is ensured that non-insulated ducts

are located at a given distance from combustibles. When passing ventilation ducts through a wall, a floor or a ceiling, it may also be necessary to fit seals and to brace-up the openings formed in the structures to this end. Such ventilation duct throughlets must not weaken or detract from the fire resistance grade of the fire compartment concerned.

It is known to divide structures, duct throughlets and details thereof into a number of fire resistance classes for fire protection purposes, for instances into classes A, B and F followed by a number, e.g. A 15, A 30, B 15, B 30. The class designation A signifies that the part of the building or structure concerned is almost completely of non-combustible material. The class designation B signifies that the part of the building and/or structure concerned includes combustible material that cannot be ignored from a fire resistance aspect. The class desig¬ nation F signifies that the part of the building and/or the structure concerned does not fulfil requirements re¬ garding maximum temperature increase on the side distal from the fire, but on the other hand decrees that hot fire gases may not leak through this part of the buil¬ ding.

The number following the class designation denotes the actual length of time in minutes that the part of the building and/or structure concerned is able to withstand heat according to standard testing.

When installing a ventilation system in a fire compart¬ ment-divided building, it is necessary to form, insulate and seal the ventilation-ducts throughlets in place in the building. This may sometimes create very difficult working conditions. A number of methods of -penetrating fire compartment-defining structures are known to the art, these methods differing in accordance with current ordinances and requirements.

A ventilation duct is normally constructed of a sheet metal tubing of rectangular or circular cross-section. The tubing is normally encased in heat insulation of fire resistance class A, although not lower that A 15, under the assumption that the protection distance from combustible material is not fulfilled. The insulating material used is normally mineral wool, and the thick¬ ness of the insulation determines the fire resistance class of the ventilation duct.

When a ventilation duct extends through part of a buil¬ ding and is symmetrical on both sides thereof, a rela¬ tively long length of insulation is required in order to meet requirements relating to the spontaneous ignition of combustible materials. It is sometimes necessary to reduce the thickness of the insulation in stepped incre¬ ments and sometimes to insulate the ventilation duct throughout its length in a room or a like space. This latter alternative is particularly applicable in those instances when insulation can only be provided on one side of part of a building. In such cases, the requisite length of insulation on the accessible side of the fire compartment-limit may be twice as long as when the insu¬ lation is symmetrically divided on either side of said limit.

It is known to fit a ventilation duct of fire resistance class A with adjustable dampers or butterfly valves of fire resistance class F, with the intention of preven- ting the spreading of fire through the ventilation sy¬ stem. However, the ventilation ducts must be insulated against fire and temperature in accordance with the aforegoing. The damper units concerned are relatively large, heavy and expensive and incur high installation costs, particularly with regard to trie work involved, such as duct fitting, damper fitting and insulating work in various stages.

It is also known to use a ventilation duct of fire resistance class F when passing through a part of a building of fire resistance class A. In this case, a damper of fire resistance class A is mounted in the cen- tre of the throughlet. The function of this valve is to enable the insulation of the throughlet to be drasti¬ cally reduced or totally omitted. The valve plate is comparatively thick and therefore will generate a lower pressure and a high noise level when open. Manipulation of the valve plate also requires the application of high torque, which presumes the use of a powerful motor with subsequent slower response times. In order to ensure that a valve of this kind will function effectively in an early stage of a fire, it is necessary to provide the fire compartment and/or the duct system with an automa¬ tic monitoring facility including smoke and/or heat detectors. The damper is expensive, however, and conse¬ quently alternative solutions are sought for in the planning stage.

Known ducts throughlets in fire compartments-walls or in like fire-break defining structures, are assembled and installed in position on site in the building itself. This procedure is both complicated and time consuming and makes it difficult to obtain a symmetrical insula¬ tion and to seal the ventilation duct throughlet in relation to the part of the building concerned when wor¬ king in confined spaces.

The object of the present invention is to eliminate the aforementioned drawbacks and to enable ventilation ducts to be let through fire compartment walls, floors and ceilings in a more rational manner and with the aid of much less expensive components than with earlier known arrangements. Accordingly, the present invention relates to a ventilation duct for passage through a structural element in a fire compartment-divided building, wherein the invention is characterized in that the ventilation

duct is a prefabricated unit which comprises an inner tubular member and an outer tubular member with a fire¬ proof insulation enclosed between said members and in that the perimeter and length of these components are given a shape so that the ventilation duct as a unit is passes through and is applied in a structural part of a building and in this respect corresponds to a construc¬ tion of fire resistance class A or B.

The inventive duct unit affords many significant advan¬ tages. For instance, it is no longer necessary to assem¬ ble and insulate ventilation ducts at the place where they are to be installed, as was earlier the norm. Furthermore, because the duct unit can be fitted with a damper plate, it is possible to reduce the length of in¬ sulation required to insulate the duct throughlet. The damper setting can be adjusted by means of a setting device mounted on the duct unit. In practice, the damper function of the duct unit is controlled by smoke or heat detectors installed in the fire compartment or in the duct system.

So that the invention will be more readily understood and further features thereof made apparent, the inven- tion will now be described in more detail with reference to exemplifying embodiments thereof and also with refe¬ rence to the accompanying drawings, in which

Figure 1 is a delimited sectional view of the duct unit; Figure 2 is an end view of the duct unit;

Figure 3 is a divided sectional view of the inner and the outer tubular members; and

Figure 4 is a longitudinal view of the duct unit.

In the exemplifying embodiment of the inventive duct unit shown in Figures 1 and 4, a fireproof material is introduced between an inner tubular member 1 and an outer tubular member 2. This material is originally a

moldable mixture of gypsum, perlite and fibre glass, which when solidified forms a solid insulating body 3 of high mechanical strength and good fire protection pro¬ perties, and enables a reduction in insulation thickness to be achieved. The insulation 3 acts to bind the two tubular members 1, 2 together to form a unit, a so- called chassis. The insulation is given a thickness at which the outer surface temperature of the chassis 4 will be so low as to render the selfignition of combus- tible material in a so-called foreign fire compartment impossible. The length of the insulated chassis shall be proportional to the cross- sectional area of the inner tubular member and therewith correspond to the requisite safety distance from the fire compartment limit, so that radiation heat or hot gases will not cause self-ignition of combustible material in the mouth of the tubular mem¬ ber in a foreign fire compartment. The inner tubular member 1 extends beyond the outer tubular member 2 and the insulation 3 at both ends of the chassis 4. Attached to each end of the inner tubular member is a ring pack¬ ing or seal 5 which enables the duct unit to be connec¬ ted to the ventilation ducts of a conventional ventila¬ tion system.

In accordance with Figure 1 a damper plate 6 of fire resistance class F is pivotally mounted midway along the length of the inner tubular member 1 of the duct unit. The damper plate 6 has mounted thereon a flange on which one end of a link 8 is pivotally attached. The other end of the link 8 is pivotally attached to an arm 9 which is attached to an output shaft 10 of a drive motor 11, which in turn is connected to the chassis 4 in a conven¬ tional manner.

The drive motor 11 and the link mechanism 8, 9 together form a damper plate setting device whose functions are controlled by signals delivered by smoke and/or heat detectors installed in the fire compartment and/or the

ventilation duct concerned. A fire resistant sealing ring 12 may be attached to the periphery of the damper plate 6. Alternatively, a sealing material which will expand in the event of fire may be disposed between the damper blade 6 and the chassis 4 and therewith eliminate the risk of leakage of fire gas.

The use of a class-F damper plate allows the plate to be made thinner, which means that no appreciable pressure drop will occur when the damper is open. Furthermore, less work is required to operate the damper and the sea¬ ling requirement relative to the part of the building concerned is also reduced. The greatest benefit, how¬ ever, is thought to lie in the cost savings afforded by a more general application of closable ventilation ducts.

Although the drawings show a duct unit of circular cross-section it will be understood that the duct unit may alternatively have a rectangular cross-section within the concept of the invention, wherein the damper valve may include one or more pivotal plates.

Irrespective of the configuration of the damper, it may be advantageous to paint or surface treat the damper plate 6. Such treatment will reduce heat emission and is therefore able to influence the length of insulation required on the chassis.

According to the concept of this invention, when instal¬ ling a ventilation system an inventive duct unit will preferably be passed through a fire compartment-limit such as to extend symmetrically on either side thereof. The damper plate 6 will then be located in the fire com- partment-limit, as illustrated in Figure 4;

With the intention of preventing the transfer of heat to and from the fire compartment, the chassis 4 may alter-

natively be constructed with a. a centrally divided inner tubular member; b. a centrally divided outer tubular member; and c. a centrally divided inner and outer tubular member in accordance with the Figure 3 illustration.

In these cases the gap between the divided tubular mem¬ bers is filled with a moldable material which forms part of the insulation 3.

It will be understood that the invention is not restric¬ ted to the illustrated and described embodiments thereof and that modifications and changes can be made within the scope of the following Claims.