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Faster RPM also increases velocity of would-be shrapnel. Either you prepare for the risk of a slowly-rotating, large rotor/axis assembly failing catastrophically, or a faster-rotating, smaller assembly shedding poorly-fastened bits from the ends of its rotor.

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Actually no.

The velocity of the shrapnel tracks the energy stored in the device. Meaning a larger radius has faster shrapnel.

Note: velocity as used in my earlier message is circular velocity, (AKA RPM), not linear velocity.

The velocity of the shrapnel is the same as the linear velocity of the part it detached from. If it detaches from a faster moving surface, it will fly faster.

Sorry for fudging may response with a term for angular velocity, instead of linear velocity. I was writing from the assumption that the primary point of a smaller centrifuge would be to safely get higher centrifugal forces at the ends of the rotor, which would require that the ends of the shorter rotor move at greater linear velocity.

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