The present invention relates to an apparatus for drawing off ground air in a volume of ground beneath or at the side of one or more houses.

Apparatus of this kind is primarily used for drawing off health-imparting radon from the earth volume to prevent this gas from flowing into the air in the rooms of the house. It is considered a risk of cancer development for human beings, and above all their bronchial passages, to be exposed to radon and radon-contaminated media.

Different solutions have been proposed for preventing radon from penetrating into houses. One method, referred to, but not described in the SSI report 87-17, the State Radiation Protection Institute, Stockholm, June 30th 1987, pp. 62-63 , involves taking up a plurality of holes in the foundation slab of the house and connecting each hole, via a duct system, to a blower situated on the roof of the building, for example. The intention with this arrangement is to lower the air pressure in the ground volume under the foundation slab of the house so that radon-containing ground air is not drawn into the house.

This known technique has several disadvantages. Due to the screening effect of intermediate walls, it can occur that several holes must be arranged in the foundation slab, which means that several ducts must be arranged, thus infringing on the space in the house. Neither can the ducts always be arranged in an aesthetically acceptable way. Another disad¬ vantage with this known technique is that the blower noise can be disturbing. In addition, there is the risk of leakage in the duct system, which means that radon-containing ground air is supplied to the room air, i.e. there is achieved exactly the opposite effect to the one sought after. Another disadvantage with the known technique is that the foundation slab can be cooled and the air in the duct system then cools

air in the rooms. There5 is .also some risk that frost action occurs under:the ^: house and the water pipes to the house freeze.

The object of the invention is to achieve an apparatus of .the kind mentioned in the introduction, which avoids the disad¬ vantages in the known art in this field. The distinguishing features characterizing the invention are apparent from the accompanying claims. By placing the inventive apparatus on one side of the house at a depth of about 3-4 metres, there is obtained a considerable ground volume from which the blower draws off the ground air and the radon in it. The blower is situated outdoors and its noise does not disturb the occupants of the house.

The magnitude of the volume from which the apparatus . in accordance with the invention draws off the ground air is naturally dependent on the nature of the ground, the suction capacity of the blower, the pipe dimensions etc. With moderate dimensioning of piping and blower, it is however possible that a single apparatus can serve several adjacent houses.

The invention will now be described in more detail and with reference to the accompanying drawing, where

Figure 1 is a cross sectional view illustrating an embodiment of the invention.

Figure 1 illustrates a cylindrical tube 1 of sheet metal, plastics or other material, which at its lower end is provided with two rows of holes 2. The holes in the rows are staggered. The tube 1 is open downwards and is upwardly provided with: an airtight cover 3. A blower 4 is arranged in the upper part of the tube. The blower is mounted over a suitable aperture in a disc 6, which in turn is placed on an internal ring 5, arranged on the inside of the tube. A stub pipe 7 is arranged on the tube 1 above the blower and is in communication with the space 8 above the blower 4 in the tube. An evacuation duct 9 is mounted on the pipe stub 7 such as to extend above the

ground surface 10 a distance attaining to 3-4 m. The upper part of the evacuation duct 9 is suitably arranged, for aesthetic reasons, in connection with a wall on the house 11. Plastics film 12 is laid round the tube a distance above the holes 2 and covers the surface of the unillustrated (refilled) hole which was made when excavating for the tube 1. The downward, suction side of the blower 4 has a sub-pressure within the range of about 15 to about 60 mm water column, and draws off the air, which there is in a ground volume under, and on one side of the house. This ground volume can laterally have an extension, depending on the nature of the ground, which can attain 50-100 m in diameter. If the ground air within the mentioned volume contains radon, this gas will thus be sucked up through the tube 1 also, and depart via the evacuation duct 9. A sub-pressure is created under the founda¬ tion slab of the house. Normally, the tube 1 is placed within its bottom end about 3-4 m under ground level at a f w meters' distance away from the house. It is thus not necessary to interfere with the house, and since the blower is under ground level its disturbing noise is reduced to a considerable extent. Since the volume from which the apparatus withdraws ground air is rather extensive, the apparatus can be used to serve several adjacent houses. Several house owners can thus cooperate in the provision of a common apparatus, which means that the installation costs can be distributed over several house owners.

The cover 3 shall be mounted airtight on the upper end surface of the tube, since there is a rather large excess pressure in the space 8. The cover should be in the vicinity of the ground surface so that there is easy access to the blower for inspec¬ tion and possible maintenance. Although not illustrated in the drawing, it will be understood that there are electrical lines to the blower. These lines are suitable laid in the evacuation duct 9. An unillustrated sealing ring is arranged between the ring 5 and disc 6. The ring 5 can be welded or otherwise fixedly arranged on the inside wall of the tube 1.

The embodiment of the invention described above can be modi¬ fied in many different ways and varied within the scope of the accompanying claims. If it is not necessary to take any aesthetic considerations, the upper end of the tube can project a distance above ground level. The blower can be situated above ground level in such an embodiment.