Dont know a about avalons but I shut down my s9s and m3s trough ssh, command poweroff. Leave them to cool down and then unplug psu.
And THAT has got to be the absolute safest way!
Well I suppose it is. I just dont feel comfortable unpluging something that drains 2.2kw (like M3) without proper shutdown. Not to mention sparkling effect that is sometimes seen in the socket. Also this way chips can properly cool down, if you just unplug them while they are at 85 degrees whole miner gets damn hot.