Hello Tyler ,
When you shut down a gasifier and close all your valves it is kinda like covering a camp fire . Oxygen can’t get to the fire and it will go out after a while . If needed you can uncover and bring the fire back to life if you don’t wait too long.
I find if I am using dry hard wood I can start the gasifier without relighting up until about 3 hours .
A small amount of gas might linger in the system but not much .
Sometime there might be a burp out of the hopper and seems it may happen more at start up than any other time .
(could it possibly build pressure in the system enough to blow up? thanks, tyler.)
There will be too many places for any pressure to leak out .