The SFP modules '490NAC0100 or 490NAC0201) are the fiber optic or a copper transceivers which are used to connect the twice M580 CPU in a Hotstandby system
it's not recommended to insert or extract an SFP module while the HSBY CPU is powered on.
From an EMC point of view, if you take the SFP in your hand, this one will be charge with your electrostatic charge. So when you'll insert the SFP inside the CPU this could disturb the CPU.
=> So before insert or extract an SFC transceiver, check that the CPU is powered off.