A severe economic episode should chew through only half of Westpac's capital conservation buffer, if the bank's thinking about scenarios is plausible.Peter King, Westpac's chief financial officer, yesterday outlined at an investor briefing the bank board's preliminary thinking on the reviewing of capital ranges required from 2016, once the 3.5 per cent capital conservation buffer comes into force. This includes the one per cent surcharge for domestic systemically important banks.King explained that the bank's  "preferred buffer for normal times" would be "above the capital conservation buffer", which means a core equity tier one ratio of at least eight per cent.This ratio was 8.8 per cent at March 2014.He said the "risk appetite for a severe scenario" would be to "not be below the mid point of the capital conservation buffer."