Double glazing windows typically comprise an outer window pane and an inner window pane spaced apart from the first window pane, with a sealed space between the window panes. The sealed space typically holds dries air or other gas and serves for improving thermal isolation of the construction in which the window is installed. The gas is dried so as to eliminate condensation within the sealed space.
Such double glazing windows may be fixed window systems (wherein the framework is fixed within an opening in a wall and the window is not capable of being opened), casement window systems (swingably or tiltably opened), or sliding window systems.
The ever-growing threat of what was in the past refried to as non conventional war, namely chemical and biological war, has led to some recent requirements to provide blast-resistant and gas-tight window systems. In addition, it is often a requirement that such window systems also have improved resistance to impact hazards, such as, for example, resistance to bullets fired from firearms, shrapnel of explosive charges and bombs, and even vandalism, e.g. attempts to break into a building or crowds trying to brake through.
A variety of windows offer blast resistance and impact resistance solutions, most of which typically offer a single type of protection, namely blast resistant or impact resistant. Other window systems offer dual protection but do not provide the climatic benefits of double glazing window systems. One considerable disadvantage of known window systems is that a single, reinforced impact-resistant laminated window absorbs also some of the blast energy (owing to its relative rigidity) and in many cases may forcefully fly into a room causing severe damage and casualties.
Furthermore, for fixing a reinforced laminated window of the aforementioned type within an opening in a wall, a suitable structure and reinforcement of the opening are required, which at times are not feasible for retrofit.
U.S. Pat. No. 3,624,238 is concerned with a bullet resistant structure of laminated character comprising outer faces or piles of safety glass with an intermediary ply formed of a polycarbonate a resin.
U.S. Pat. No. 4,312,903 deals with an impact resistant double glazed structure and is concerned in particular with the thickness of the layers of the laminated window panes, and their chemical compositions.
U.S. Pat. No. 5,059,467 is concerned with a protective ballistic panel including a first-impact, front layer and a second rear layer. The layers being spaced from one another by a semi-elastic material, defining a sealed space. However, the panel is for use as a personnel protective shield and is not concerned at all with providing blast resistant protection or with serving as a window system.
U.S. Pat. No. 4,625,659 discloses a bullet and explosion proof window or door system comprising two spaced apart panels, whereby the outer panel is spaced from a support soffit such that a gap is formed for providing a ventilation channel. However, peripheral portions of the panels are fitted with a security layer in order to prevent projectiles from entering through the ventilation gap.
It is an object of the present invention to provide a window system offering impact and blast resistance whilst not interfering with its function as a window, namely, providing good visibility therethrough as well as good climatic and acoustic isolation between an in-side and on out-side thereof.