In a grain silo, the top layer may appear hard and it may appear that everything is solid below you. However, there could be voids and the grain underneath is still loose. You can easily break through, get trapped, and suffocate in grain. This image actually appears to be from the wikipedia I came to link, heh: https://en.wikipedia.org/wiki/Grain_entrapment
3 minutes to suffocate as well According to the Wikipedia your only chance of survival in that situation is to attempt to find or create a airpocket
One guy whom had a dust respirator was trapped for 5 hours sliping in and out of consciousness sounds terrifying not having control of your limbs stuck upto your head in grain alone in the freezing pitch dark and the risk of hypothermia or suffocation looms over you what a way to go
I wonder how much adrenaline your body can produce. I'm not looking to find out. Some people, though. Like people who go snow boarding/skiing on remote mountains and get trapped in the snow.
Yeah I am not looking to find out either and it sounds like a miserable way to go out. But I also like skiing.
So personal tip, you can spit to figure out which way you are oriented because being upsidedown cclan cause you to lose consciousness faster from blood pooling in your head. If you are trying to flex to keep blood flowing, you can try to wiggle your wrists and arms slowly to pack the snow and see of you can push against it but you can risk slipping in further.
And if you are deeply in the wilderness give people your exact schedule and wear a device that allows for people to locate you without you having to do anything. Honestly the same can be said for working near or I'm grain bins