There are different kinds of safety hooks that exist for different purposes. Two very different ones are shown in the link above. Both of these are used in personal tethers that are used for "via ferata" type mountain climbing & offshore boat racing safety. Each type is there for a different reason.How do you define a safety snap?
My understanding is that it is a safety against accidental unhooking. English is not my first language so could be wrong.
Do you have a source for the tensile strength to break for it to be safe for towing a flag?
Stainless steel hardware snap hooks safety | Wichard Marine
All our references in Stainless steel hardware snap hooks safety at Wichard Marine ! Quality products ensuring safety and performance for more than 100 years.marine.wichard.com
Double action safety hook - Fluorescent - Length: 115 mm | Wichard Marine One that looks like this is used for the end of the tether that attaches to the jack line or safety cable. These are designed to not come off by accident.
Snap hook with fixed eye - For 20 mm webbing - Length: 44 mm | Wichard Marine One that looks like this is attached to the harness on the person. These are designed so that they can be released under load. I will tell you from personal experience, that releasing these under load is not always an easy thing. I tried to release one while getting dragged behind a boat several years ago. It didn't go well. I now use shorter tethers that don't let me get past the edge of the deck so that I will not be likely to need to deal with that issue again.
I would not use either of these two hooks for the safety break away purpose being discussed here. The second type would be a better choice than the first type, but only in the same way that a broken finger would be better than a broken arm. I would prefer neither rather than choosing between those two.
