Remember, there is a marked difference between guards and screens. Guards are simply for avoidance of operator contact with moving machinery/parts. Screens are there as alternatives to PPE, or where others, without protection from flying chips, might approach within range.
Guards need to be fixed such that they are not easily removed without tools – or, movement immediately halts the machine operation and removal prevents the machine from starting.
Guards, I would suggest, are compulsory from the elf’n’safty point of view while screens are dependant on other factors – like getting splashed by coolant is different than a mangled hand after contact with moving machinery.