Can someone explain this please: (From ASME A17.1-2013)

2.26.1.5.1 When switching to either “BYPASS” or “OFF” position, they shall
(a) have contacts that are positively opened mechanically; their opening shall not be solely dependent on springs, or
(b) be SIL rated with a SIL equal to or greater than the SIL indicated for the applicable device shown in Table 2.26.4.3.2