How to get someone to suffocate faster
I’m writing a murder mystery. The case I’m having trouble with has a character suffocate in a very tight, poorly designed, system of tubes. The problem lies in the fact I need her to die within a four hour window and I need the killer to be certain she will die within this four hour window. I know suffocation like this typically takes longer, so I need a way I can get her to die faster. So far I’ve made it so she’s positioned upside down, has a concussion, and is gaged. Is there anything else I could do?