A post below made me think of this. When I was a kid, I did about 2 minutes. These days, I can hit maybe a minute. SST...Ever have a scary situation while diving? As a Firefighter, I always worried about being stuck in a bad environment while wearing my SCBA. During Fires, I often practiced controlling my breathing while exerting myself (That could be a BOOGER!) Something I would do that looked silly as hell without a mask would be to sorta pucker or raise my upper lip / gum towards my nose. Sounds silly but it helped.