I don't think this would play out the way you're thinking. Regardless of the incorrect perception of the 30 meter depth, you would still need to be considerably deep to get caught in one of these nets. Again, if you're there without any tools and you're that deep, fuck man the only thing I can say is do not do that lol. There's a reason saws are very common on a variety of vessels, ocean or otherwise. Divers are definitely trained to carry cutting tools on them, I know I was taught to carry a dive knife and wire cutters — to be honest a saw doesn't sound ridiculous.