Case Study: Nickel Sulphide Inclusion | Shattered Glass Balustrade | London |

Phil-Rock-01
Jan 20
3 min read

Replacement of a shattered glass balustrade on the balcony of a luxury apartment high rise in London.

The glass balustrade was fine at bedtime, but without evidence of an incident, the single balustrade was shattered in the morning.

Rock Maintenance safely removed the damaged balustrade and installed a new glazed unit. It was discovered that a common culprit was the cause of the breakage. Nickel Sulphide Inclusion (NSI)

What is Nickel Sulphide Inclusion (NSI)?

Nickel sulphide inclusion is a deposit of residue formulated during the production of float glass - like that used in the balustrade. Microscopic mineral deposits formed in the heat of the furnace during the production process of glazing. The resulting deposit is a fault that interferes with the usually resilient glass integrity causing issues like uneven heat dissipation of the glass and a weak point in the structure. ¹

What is glass made from?

Glass is made from natural minerals such as Silica, Soda ash, Dolomite, Limestone, and Cullet. Glass has been made to increasing degrees of clarity and quality for over 3000 years. The methods used today are similar to those first used by our ancestors. In basic terms, minerals are heated in a furnace to combine in a liquid form, then formed into the required shape and the cooling controlled to ensure strong glass. Despite extreme effort and thorough methods to isolate the individual minerals required to produce glass, minuscule impurities can remain. In the heat of the furnace (up to 1600 degrees centigrade), these impurities form nickel sulphide and are permanently sealed within the finished glass pane.

What stresses can glass resist?

12mm safety glass, heated and cooled correctly in production to be ‘toughened’, can withstand around 90MPa’s - (90 Newtons per square millimetre).

This is plenty to withstand negative and positive wind pressure, knocks, bird strikes, tennis balls, maybe even something more substantial coming into contact with it.

But, with a very specific set of conditions, the integrity of glass can be compromised.

How did the balustrade shatter?

Glass is much more flexible than most people realise - It warps, flexes, contracts and expands to incredible tolerances. NSI disrupts the integrity of the usually resilient glass. NSI causes a weak spot in the structure of the glass. A point where the stresses applied to the glass is focussed - irregularly. In periods of extreme cold or heat, a sudden change in temperature, a gust of wind in the right direction, even vibration from passing vehicles can cause the glass to shatter at the nickel sulphide deposit. This is what happened to the exploding balustrade.

What can we do about NSI ?

Very little - incredible efforts are made to ensure purity of materials used for the production of glass. Here’s some examples of the measures taken by the automotive industry in the United States in their glass production:

1. Green sand transported by railroad is processed through several filters to remove nickel in mineral form or perhaps from stainless steel tools, nuts, bolts, washers. (Stainless steel cannot be detected by magnets).

2. Bulk recycled glass is inspected in a similar way.

3. Every machinery maintenance procedure is carried out by staff trained to avoid contamination with nickel. Training is intense to ensure all workers understand how to prevent contamination of the plant.

4. Use of any nickel containing tool or material anywhere in the Ford Glass float facility was closely controlled to prevent contamination.

5. NSI can only be found with a Scanning Electron Microscope. If there is a chance of contamination, the glass is scanned and the contaminated glass destroyed.

How an Rock Maintenance help?

Rock maintenance has the experience and skill to replace architectural glass anywhere. From commercial shop fronts, to luxury high rise apartment glass, Rock Maintenance specialises in specialist access and bespoke glazing.