He seems to be doing it fairly safely by having it housed in a building a whole 50m away from the main dwelling. A fire from there could spread to the house or elsewhere but it's no longer a metal fire so it's a lot easier to deal with and just contain the fire in/around the shed. I'd probably add a nice gravel buffer around it to help that and live in a reasonably well hydrated part of the country so there's not as big a fire risk from embers.

Great if you are a skilled electrical engineer who owns a bunch of land somewhere that doesn't have any fire risk.