The history of toughened glass in overhead glazing is shrouded in myths about nickel sulphide, and the HSE appears to have lost its way (NCE 17 February).
A toughened glass panel is considerably harder to break than any other glass panel of equal thickness. It has vastly superior resistance to thermal stress, which is another reason why it is used extensively in roof applications.
If toughened glass breaks, it disintegrates. The weight which would hit a person standing underneath would be far less than the weight of other glass types.
When laminated glass breaks, it should stay in place. But if impacted by an excessive load, the whole piece may spring from the frame, and a much heavier weight of glass will hit any person unfortunate enough to be standing beneath.
Provided that the glass, frames and fixings are designed to meet the service loads, glass will stay in place in a roof unless vandalised or subjected to an Act of God. It seems, therefore, a gross over-reaction by the HSE to demand the replacement of overhead toughened glass by laminated.
John Weir, standards secretary, Glass & Glazing Federation