Gary R. Lloyd wrote:

Canada's IDEAS (post R2000) air infiltration standard specs 0.15 m^3/h
per m^2 of envelope, tested at 50 Pa, which translates into a natural air
leakage of about 2.5 cfm, or 0.008 ACH for a 2400 ft^2 1-story house,
125X less than a typical 1 ACH US house.

Is that enough fresh air to sustain life?

Almost. Early UK coal miners fell asleep with less than 5 cfm each.

Current ASHRAE humans require 15 cfm.

Nick