New materials, new technologies and deleterious materials

Posted: 16/11/2012


Those procuring new buildings or new infrastructure are generally well aware that the use of certain materials should be avoided. These materials are generally described as “Deleterious Materials”, and they are sometimes referenced as “Prohibited Materials” in some building contracts. Such materials might fail, or cause the fabric of the building or infrastructure to fail, or they may cause harm to individuals and their use should be avoided wherever possible.

On more straightforward projects, the approach has long been to define deleterious materials by reference to what became known as the 'Ove Arup Guide', or the Good Practice in the Selection of Construction Materials published in 1997 and authored by Arup & Partners. That guide was updated last year and it is recommended that reference is now made to Good Practice in the Selection of Construction Materials 2011, now authored by Hoare Lea and Partners.

Sometimes, at the time materials are used, they are not known to be problematic. One good example is asbestos, which was used extensively throughout the 1960’s and 1970’s until its long-term harmful effects were more widely understood. One more recent example is in glazing materials, where advances in manufacturing processes brought about an improved product - but with unknown serious consequences.

Advances in glazing manufacture led to increased use of heat-treatment, to create strengthened and tempered safety glass. This was welcomed by architects and designers working on an increasing numbers of glass façaded commercial projects across the City, and across the country. Some time after the new product had been introduced, it became apparent that the manufacturing process had led to an inherent problem not initially anticipated. Microscopic particles occur in glass and they are impossible to avoid completely. These are termed inclusions, and the manufacturing process leads to some inclusions comprised of nickel sulphide. As part of the tempering process the glass, and the inclusions, are heated to high temperatures, but after rapid cooling the nickel sulphide inclusions remain in a high-temperature (or alpha-phase) form. At time of manufacture this isn’t problematic as the structures are microscopic, but over time the nickel sulphide inclusions return to a cold-temperature (or beta-phase) form and they expand, increasing in volume and causing panes to shatter – apparently spontaneously.

Often, office workers would return after the weekend, when the building’s heating was turned off, to find random panes shattered for no apparent reason. Sometimes the inner pane of a triple glazed unit would shatter leaving the outer panes intact and leaving the conundrum of what caused the failure. Nickel sulphide inclusions are now well understood by specialists and by glazing manufacturers, and BS EN 14179-2:2005 now requires a heat-soak process that generally eliminates the problem.

At the time, as this glazing wasn’t known to suffer any problems, those putting contracts together or specifying materials didn’t seek to exclude tempered glass – they actively specified it. However, problems soon arose with many glass panes shattering with a signature “butterfly” shattering caused by the expansion of nickel sulphide inclusions. There were notable high-profile failings, often on a large scale. For example at City Hall, home of the London Mayor, and at Waterloo Station, then home of the Eurostar. The problem became so widespread that the occurrence of nickel sulphide inclusions was dubbed “glass cancer” by the construction press. A number of large projects were significantly affected, and the only remedy was to replace glazing units - often in, what were by then, fully operational commercial buildings.

It is not surprising that remedial works caused massive inconvenience and huge expense. But what was the remedy for building owners? The answer wasn’t always clear. Building contractors had installed what they were contracted to install – such glazing had usually been specified. Architects and designers had specified the glazing but often they hadn’t been negligent as the problem wasn’t widely known at time of specification. On larger projects, some owners were astute enough to procure collateral warranties direct from the manufacturers and so they generally found remedies more readily. On smaller projects this wasn’t the case and owners often struggled to find effective commercial resolutions. Nickel sulphide inclusions therefore provide a cautionary tale about adopting new materials in to any new building or infrastructure. If new materials are included, consideration should be given to securing extra contractual protection to the employer – such as direct warranties from the manufacturers.

It is clear that those procuring projects will need to take care when considering using new materials. Special care is also required when procuring new technologies. Many materials may be perfectly harmless when used in normal circumstances but they may not be suitable when used in unusual, special or new situations. For example, many new technologies involve chemical or biological processes and materials may react and respond differently, and they themselves may be adversely affected by the chemical or biological process.

The growth in renewable energy projects has led to a large number of new biogas projects. Often these are procured on an EPC (Engineer, Procure, Construct) basis because the technology provider is the only party that has any real degree of knowledge of the process. New employers may know that they want a plant capable of producing a certain amount of electricity, but they may have a limited knowledge of how the technology really works. Sometimes an employer can turn to consultants expert in the area, but this isn’t always possible. The employing client is therefore largely reliant upon the sector knowledge, and design capability, of the EPC contractor.

In these circumstances, it isn’t possible for the employing client to list unsuitable materials because the client simply doesn’t have that expertise to know which materials are suitable when used in this new technology. Here, the client has no alternative but to rely on the expertise of the EPC contractor. The employing client will therefore need to ensure that the EPC contractor adopts good industry practice, and that the EPC contractor is judged by reference to knowledge that he should have as a specialist in that sector. So, for example, with regard to a new technology such as anaerobic digestion, the client is unlikely to be able to fully list all materials that are likely to be deleterious. As such, the EPC contract will require careful wording of the “Deleterious Material” or “Prohibited Material” provision to be clear that the contractor is held to operate to that standard that would reasonably be applied by a contractor designing and constructing in the specialist field of anaerobic digestion, and that materials are not used in construction that might adversely affect the effectiveness of the plant, or that might themselves be adversely affected by the technology.

It is often said that the pace of change is quickening. In times of new technologies and new materials, those procuring new buildings or new infrastructure should take extra care when preparing their contracts.


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