"nightjar .me.uk>"
Ordinary kitchen chair, right? Unsafe to step onto it because the step is too high? Oops, better stop doing any hillwalking, scrambling, climbing, caving then - they're clearly too dangerous. And don't let anybody see I rarely take staircases one step at a time.
re the material - I'd suggest that one should be obvious - eg I probably wouldn't stand on the rather tired one with the frame coming apart which sits in the shed as an occasional doorstop, but I'm entirely happy about standing on the chairs in my kitchen a.t.m. (solid seat with cushion - take cushion off before standing on it).
And yes, I could write a formal risk assesment for those decisions in a working environment as well as home.
cheers, clive