Three standards you need to worry about. Can't be arsed to check the numbers, sorry.
1. The industrial one. A crap standard, which forbids the decent chinstraps (for trapped miners' sake) essential for work at height, and only requires a couple of cursory drop tests right on the centre top. This is the reason most cheap site hats have a central ridge. If it misses that, you're fucked. Other requirements are for protection against live wires and spatter - i.e. ventilation holes not allowed.
2. The mountaineering standard. Decent chinstrap required. More drop tests, from greater heights and varied angles. A decent standard, but aimed at protection from falling objects, not so much head protection in a fall.
3. The cycling standard, which is all about head protection in a fall.
Decent lightweight climbing helmets will meet 2 and 3. Old school lids just 2. Most rope access lids meet a combination of 1 and 2 (e.g. strong chinstrap, no holes, less drop tests), though you can justify using 2 and 3 in your risk assessment as appropriate - i.e ventilation more of an issue than hot works or electrical cables. Jobsworth safety officers who don't like chinstraps = undo it when on floor.
