IRA Bombing, Manchester 1996: a tale of two shop fronts

One storefront (left) used annealed glass while the other (right) used laminated glass.

When the Irish Republican Army (IRA) bombed Manchester City Center in the summer of 1996, investigators recorded the damage. UK Home Office blast expert Nick Johnson told LGN: "There were two shop fronts at approximately 80 m from the explosion. One shop front used 10 mm annealed glass while the other used 11.5 mm laminated glass. The laminated glass crazed but stayed in the frame while the annealed glass broke and sent hazardous glass shards flying inside and outside the shop. To my mind, this is an excellent case in point for shop fronts to use laminated glass."

Following this incident and similar ones, UK Government bomb blast experts have worked with Security Glazing Committee specialists on European (CEN) and International (ISO) standards for blast-resistant window systems. They propose that a key test for an ISO Standard should involve a 100 kg TNT equivalent charge at 25 m against a test window of about 1.5 m 2 .

Johnson said: "In this test we found that a sealant-bonded, 7.5 mm thick laminated glass window pane remains firmly in place. An insulated glass unit of 6 mm toughened glass plus 7.5 mm thick laminated glass with a gasket also remains in place. For each, the frame has to be strong enough and provide about 30 mm edge cover, where the edge cover is usually about 5 m less than the physical depth of the frame rebate (the slot where the glass is placed).

"For comparison purposes, and using the same charge threat, a 6 mm + 6 mm annealed glass insulated glass unit would be a dangerous option, in that it would send shards of glass flying in all directions up to 40 m away. Meanwhile, a 6 mm annealed single glazed unit would be even more dangerous, sending flying shards as far as 70 m away. Our standard policy is therefore to recommend the use of laminated glass in new or refurbished Government office buildings."