What is it that makes BIP149 safer to activate than BIP148?
BIP 149 is different in that it does not enforce orphaning of blocks that don't signal readiness for SegWit. Instead just the supporters enforce the rules on any blocks that contain SegWit data and allow regular blocks to be mixed into the chain. Thus, miners that don't change anything will build on the SegWit chain. 

To split the network, miners would need to deliberate fork the chain, either by continuously rejecting every SegWit block and outpacing the BIP149 chain, or by mining a block with an invalid SegWit transaction that legacy nodes accept and SegWit nodes reject and building on top of that.