The present invention relates to a landing deck for aircrafts, and in particular, but not exclusively, a helicopter deck of the type used on seagoing vessels and installations, such as offshore platforms.

It is desirable to protect such decks against fire. There is always a danger of accidents and damage, to a larger extent than on airfields, because of adverse weather conditions and because the deck follows the movements of the vessel or platform. In an accident fuel from a helicopter may leak out and be spread along the deck, and the fuel may be set on fire. The ignition may lead to a serious fire, and the combustion intensity may be very high when the fuel is spread out on a relatively smooth surface, causing that the fuel exposes a large surface to the air. It is of course desirable to limit and to stop such a fire as soon as possible, and it is known to provide systems adapted to coat the deck with foam in order to stop the fire. It is of course also known to place extinguishing eguipment, such as foam extinguishers, on or near the decks, and, moreover, it is known to provide channels in the runways of airfields, for spraying of foam. In Norwegian Acceptance Print No. 139.526 is described means adapted to coat a helicopter deck with foam in order to stop a fire, whereby a framework is placed above a planar deck and a lattice work above the framework. In the cavities thereby formed below the lattice work are provided apertures for spraying of foam. The purpose of this is among else to prevent that the foam being sprayed is blown away without giving any fire extinguishing effect.

Thus, the known systems first of all concern means for extinguishing a fire in fuel which has been spread along a deck.

The object of the present invention is to provide means leading to a reduced intensity and duration of a possible fire on a deck, said means being "passive" means included in the deck, i.e. means which without any action are operative in case of a fire, without the need of starting the operation of an extinguishing system. The invention is, however, not restricted to the use of such means separately, and "active" means, such as a foam spraying system, may be used additionally.

Said object is achieved by means of a landing deck as defined in the succeeding patent claims.

The invention is among else based upon the fact that the combustion intensity by the combustion of a certain amount of combustible liquid usually increases with the size of the free surface of the liquid, and that said intensity is not influenced by the depth of the liquid below said free surface. Thus, it is in the principle possible to restrict the intensity of the combustion by restricting the free surface.

Moreover, the combustion intensity of a liquid in a container which is open at the top will depend on the ration between the size of the upper aperture of the container and the distance from said aperture to the liquid surface. When the container aperture is sufficiently small relatively to said distance, combustion on the liquid surface will extinguish by itself after a short time. In containers having equally large upper apertures the combustion intensity will decrease with increasing distance to the liquid surface.

A main idea on which the invention is based is to take advantage of these facts, by providing grooves in at least some of the beams of the deck, in order to reduce the combustion intensity. Another main idea is to drain the liquid rapidly from the deck during a fire, in order to reduce the amount of liquid set on fire.

Thus, when combustible liquid, such as helicopter fuel, is spread on a deck constructed in accordance with the present invention and set on fire, the liquid will very rapidly flow down into the grooves. Only portions of the beams remaining between the grooves will be wetted by liquid, and said liquid will either burn or vaporize. Most of the liquid will flow down into the grooves. There, the liquid may burn, but with a much lower intensity than when burning on a planar deck surface without grooves. Moreover, the liquid in the grooves is protected against the radiation heat from liquid burning on the deck surface, and it is possible to achieve that most of the liquid is drained from the deck without being set to fire. For the purpose of the drainage the deck may have an inclination, and collecting gutters or manifolds may be provided in order to collect liquid from all the grooves and to direct it away from the deck.

When a deck in accordance with the invention is constructed of extruded beams of aluminium or an aluminium alloy the grooves may of course be formed during the extrusion. The same applies to steel beams. For beams formed in another manner, for instance by rolling, the grooves may also be formed by the manufacture of the beams. To the extent it is warrantable with respect to strength and stability grooves may also be formed in existing decks, e.g. by milling, or by sawing through the beams and subsequently mounting of gutters on the underside of the beams, below the sawn slits.

The grooves may be undercut, i.e. have an upper opening which is narrow relatively to the space below the opening. Thereby the supply of air to the grooves will be choked, and simultaneously the volumetric capacity of the grooves will be large.

When the invention is used on floating installations which may move in such a manner that the inclination of the deck is changed, the deck should be inclined in the direction of the

grooves, from the middle towards each end, or from each end towards the middle, in order to secure that drainage of the liquid is achieved. Inclination merely in one direction towards a manifold brings about the risk that the inclination may be "negative" because the installation takes an opposite inclination.

In order to further increase the effect of the invention the surface of the beams may be inclined in the transverse direction, towards the grooves, so that the liquid flows rapidly down into the grooves.

The invention will hereinafter be explained by means of the accompanying drawing, showing the cross section of a deck beam for the construction of a deck in accordance with the invention, and it will be appreciated that several such beams are placed side by side in order to constitute the deck.

The beam shown, which may appropriately be made by extrusion of metal, comprises two -upper flanges 1, 2, a lower flange 5 and a web 6 , and two channel walls 7 connect the web and each of the upper flanges 1, 2. Thus, the channel walls 7 define a groove 8, which at the top is open through a slit 9. Along the edges of the upper flanges 1, 2 are shown a slot 3 and a tongue 4, respectively, for joining to corresponding beams, possibly by placing of sealing means between the beams.

As shown, the two upper flanges 1, 2 are inclined in the transverse direction, inwardly towards the slit 9. This brings about that liquid on the upper side of the upper flanges will flow rapidly towards the slit 9 and therethrough.

The beam shown has a cross section in which the walls 7 defining the groove 8 constitute supporting parts of the cross section. Within the scope of the invention the grooves 8 may of course be formed in more massive beams, and the grooves may have substantially smaller cross sections than the one shown,

relatively to the main dimensions of the beam.

Additionally to grooves for the drainage channels may also be provided for supply of foam for fire extinguishing.