Geoff, I don't have access to the standards to check the exact wording, but I'd suggest the best standard to look at is IEC (or BS EN) 61010-2-020.
In any event, you must be sure that the machine will protect the user, even if the user is blind, drunk or blind drunk.
Lids cannot be allowed to be opened whilst the machine is spinning for obvious reasons, but there are other aspects of the standard where inference is given to certain safety considerations but the phraseing given is often very vague.
For instance, not all machines can boast sample containment in event of a disruption. If you are spinning high risk samples, even in small machines, a lid seal and motor seal are paramount to ensure the sample remains contained within the bowl.
You pays your money, you takes your choice...
