Flexible structural adhesive prevents glass shattering at Heathrow Terminal 5

Glass is one of the most striking features of Terminal 5 at Heathrow Airport, but also a potential vulnerability. In the event of a terror attack shattering the glass, a high percentage of injuries in an explosion or bomb blast are caused by flying glass fragments rather than any incendiary device itself. Ensuring that can’t happen is a bonding solution from Advanced Adhesives.

Opened in 2008 and with a capacity to handle over 30 million passengers a year, Heathrow Terminal 5 was designed by Rogers, Stirk, Harbour and Partners. As a design feature, it makes extensive use of glass, not just as a fascia for the building itself but also within the terminal. Numerous internal panels are structures all formed from glass, as well as shop windows and dividers, contributing to the bright, airy and modern feel of the building.

A key consideration for the architects, though, was ensuring that all of this glass would be resistant to terror attack, with a terror attack on a major airport thought to be a question not of if, but of when. “If it happened at Terminal 5, it wouldn’t be the bomb blast that did the real harm; it would be the flying glass fragments that would cause a high percentage of injuries,” explains Advanced Adhesives managing director Graham Crozier.

To ensure this couldn’t happen, Advanced Adhesives was one of a number of companies asked to provide a bonding solution that would hold the glass, aluminium and/or Corian sheets together so that it wouldn’t shatter and spread glass shards throughout the area if there was an explosion. “All of the panels needed a high degree of internal flexibility, which meant a bonding solution with an adhesive with a high tensile elongation,” says Crozier. “So to bond the glass to the varying substrates, we supplied our 8062 adhesive for test, which offers up to 110% tensile elongation.”

Resisting impact loads

The 8062 adhesive has a high degree of ‘inbuilt’ tensile elongation which is generally utilised in the adhesive to resist impact loads, to cope with the expansion and contraction of dissimilar materials as they heat up and cool down in operation, or to handle the climate the bonded components are operating in. This tensile elongation is also used to resist the stresses applied to a bonded assembly in operation where movement or flexibility in the components can be experienced in some applications. However, in Heathrow Terminal 5 application, the adhesive’s tensile elongation – its internal flexibility – could enable the energy from the explosion to be absorbed, holding any broken glass in place, essentially utilising the impact resistance effect the adhesive has.

The tests were carried out at RAF Spadeadam in Cumbria, where a bomb was exploded behind the bonded panel, measuring 1.2m by 2m. “It goes without saying that we’ve never had an application like this one, and honestly we had no idea what would happen,” says Crozier. “The bomb exploded, the panel flexed, but it didn’t shatter and spread fragments of glass. We were shocked and excited – ours was the only adhesive that passed the test.”

The result meant that by using 8062 adhesive, the architects could specify standard glass for the project rather than blast resistant glass, at a massive cost saving. “The glass fronting on a shop, for example, could cost upwards of £50,000 if you had to use blast resistant glass,” says Crozier. “Being able to use a more standard glass product was a huge saving.

“Customers come to us precisely because they need a solution to something that can seem almost impossible,” he concludes. “But we are adhesive experts, and we’ve yet to find a bonding challenge where we couldn’t formulate an appropriate solution.”