It is not the most secure of fences as anyone with a spanner can make a gap (and during your BJC at least 2 of the jugglers who should know better, will do just that).
400m of Heras complete with base blocks and clips weighs 3/4 of a ton, so many volunteers can help here.
At BJC 2008, one guy from the venue put up 1km of Heras in 1 day. He had a big trolley that he used to move the stuff around. More normally it can take six volunteers with no trolley one day. If it's cold or wet, a big supply of rigger gloves will help.