HANK you for your very illustrative pictures (September 20) showing the scaffolding collapse in George Street, Glasgow, particularly as you show standing scaffolding in the background, depicting the good and bad faces of scaffolding.

The standing scaffolding shows transverse diagonal bracing which ensures that the rectangles stay rectangles and do not deform into trapeziums, as every schoolboy knows. It is especially this bracing, across the width of the platform, which is so often left out, with the whole scaffolding tending to fall backwards, away from the building.

Council engineers ''solve'' this by bolting the scaffolding on to the building, and sometimes the falling scaffolding takes the wall with it, as has happened in Princes Street, Edinburgh.

Now your picture shows an alternative type of collapse, because the outside uprights have buckled, due to the lack of the same transverse bracing. The parts bolted to the wall have been torn asunder.

Without adequate bracing, one is asking for trouble. This hardly matters in the horizontal plane, where the planking provides some stiffness, and in the longitudinal plane, bracing is usually provided. It is the lack of transverse bracing which causes most of the collapses, time and time again.

You mention Mr Hedley Horsler of the Health and Safety Executive, who expressed concern in the words, ''We can't keep relying on luck''. Perhaps you could pass a copy of this letter to him.

Thomas Gardner,

145 Bruntsfield Place,

Edinburgh.

September 24.