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Glass & Glazing – Part N


Glass & Glazing

Protection against impact – N1

Glazing, with which people are likely to come into contact whilst moving in or about the building, shall:-

a) If broken on impact, break in a way which is unlikely to cause injury: or

b) Resist impact without breaking: or

c) Be shielded or protected from


All glazing which is highlighted in the shaded areas of the diagram above is subject to the requirements of Part N1. The exception being small panes which have a smaller dimension not exceeding 250mm and an area not exceeding 0.5m2 each measured between glazing beads.

Testing & Classifications

The impact safety performance of glass is determined in accordance with BS 6206. It requires that the glass does not break or breaks safely when subjected to impact from a lead-shot filled bag weighing 45kg, Three classifications levels are achievable, with Class A being the highest.
BS EN 12600 is the new pendulum impact test standard for classifying flat glass products by performance under impact and by mode of breakage. In the future references to BS 6206-4 and relevant Building Regulations (e.g. Part N in England and Wales) are likely to be superceded by BS EN 12600:2002.

BS EN 12600 is similar to the swing bag test in BS 6206 a weight cushioned with two rubber tyres is allowed to swing at the glass from 3 heights.

Classification 3 – Drop Height 190mm
Classification 2 – Drop Height 190 and 450mm
Classification 1 – Drop Height 190, 450 and 1200mm

The three-part classification (e.g 2(B)2) is defined by;

First digit is the Drop Height classification (i.e. 3, 2 or 1) at which the product did not break or where it broke in accordance with the first two types of breakage as follows:

a) Numerous cracks appear, but no shear or opening that allows 76mm
dia sphere to pass through when a maximum force of 25N is applied. There is also a measurement of glass spall weight taken after a period from the impact.

b) Disintegration occurs and the 10 largest crack free particles are collected within a period after impact and weighed all together and found to be under a prescribed limit.

Second digit is the mode of breakage defined as:

Type (A) – numerous cracks appear forming separate fragments with sharp edges, some of which are large. Typical of annealed glass.

Type (B) – numerous cracks appear, but the fragments hold together and do not separate. Typical of laminated glass

Type (C) – disintegration occurs , leading to a large number of small particles
that are relatively harmless. Typical of toughened glass.

The third digit is the highest drop height at which the product did not break or when broke, broke in accordance with the style of break a) from the paragraph 1) above. If a glass breaks at the minimum drop height and the breakage is not in accordance with style of break a) from the paragraph 1) above then the last classification figure is zero.


Laminated glass maybe 2(B)2

Toughened glass maybe 1(C)3