I know what you mean. I too have had hundreds of troops out on parade grounds all day. Not a single fall out or issue. The troops are told to pre-hydrate and we kept an eye on them. Water was available throughout. Sitting in a shaded arena and listening to a devout Marxist would give me nausea and vomiting, but it wouldn't be due to heat.
If anything, passing out would be a blessing under those circumstances. I know that after the first hour, I'd have locked my knees and started counting backwards from 100,