subject: How To Make Glass Safe In The Event Of Unexpected Breakage [print this page] Most overhead glazing to be found in our many shopping centres and public buildings is heat tempered toughened glass. This type of glass is the material of choice as opposed to laminated glass because of its lighter weight however the downside to this type of glass is fragmentation in the event of breakage.
Breakage can occur for a number of reasons including vandalism and accidental impact however the main cause can be viewed as something of a phenomenon. Spontaneous breakage of toughened glass is the collective name given to sudden shattering for no apparent reason. In actual fact there are several possible contributory factors that can lead to such an event, these being edge damage during installation, tight fitting of glass in the frame, wind load and something called nickel sulphide inclusion.
Nickel sulphide inclusion is the occurrence of impurities left within glass during the manufacturing process. These can be in the form of tiny stainless steel shavings left behind by the machinery used in the manufacturing and handling processes or minute pieces of brick from the inside of the heat furness.The presence of these inclusions will often in time cause an anomaly with the surrounding glass during times of heat or kinetic stress resulting in an "explosive" outcome.
How do you make glass safe in the event of unexpected sudden breakage? The simple answer to this is to install a containment solution consisting of a tough polyester window film in conjunction with an edge retention system. Safety or security window film is an optically clear, smoked or reflective laminate adhered to glazing by an extremely strong adhesive. The film is available in varying thicknesses from 100 micron up to 350 micron depending on the specific requirement. For example for facilitating safe breakage of annealed glass in a door or side panel, 100 micron will achieve the necessary En safety standards as specified in Regulation 14. For "anti bandit" or blast mitigation a much thicker film is usually required.
For the purpose of glass fragment containment a 175 or 200 micron film is normally more than adequate.This combined with an edge retention system is by far the most effective solution.
There are three main types of edge retention methods used in the window film industy.They are:
1/ Aluminium profile - An angled aluminium bead held in place with a high specification double sided tape. One side bonded to the newly filmed glass and the other to the window frame.
2/ Two parallel plastic beads held together down the centre by a flexible plastic fillet. This again enables one edge to be bonded to the glass using the same double sided tape and the other to the frame.
3/ Structural Silicone - A large fillet of a highly aggressive structural silicone such as Dow Corning 995 is applied to the frame and the filmed glass. From an aesthetic point of view the aluminium profile is probably the best method as this can be powder coated to match the existing frame colour however not all frame profiles allow for this method to be adopted.
Providing that safe access to the glazing can be achieved, the application of window film with edge retention is the only realistic way of countering a very real problem.
