around 2.5x the floor thickness so 22mm would be 50-55mm x4.5 or 5mm [2"xno8 or 10]
keep in mind safe zone is within 50mm off the surface but other wires pipes or services can be any where at any depth
safe zones dont get marked as they are greater than 50mm below surface mostly through stud walls
when it comes to floors you always assume pipes cables and services at zero depth and work accordingly
going as near as possible to old fixings for extra support is a good idea as it reduces the risk off finding a service but can still go wrong
mark with chalk on walls and the flooring where services are and avoid the 30mm either side if possible
if you are going flooring on top off flooring choose a screw 5mm less than the combined thickness to allow a 3mm countersink without danger but wont help iff you find a servivce channel shaved under the floor board
never used them to be honest
i use general 4.5mm-5x50 like these from axminster or any other source like tool station or screwfix
others will have other ideas and will comment
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