3 hours ago, Rakaydos said:A typical submarine experiences far greater pressure differential than a spacecraft. A quick gogle says 700 PSI at 500m. Space to sea level pressure is 14.7 PSI. And subs have been made out of steel since at least 1775.
The information about concrete was simply for context, you could use a similar material such as steel and I would be very surprised if the concrete doesn't have steel rebars. Reinforced concrete gets used in buildings because it's good in compression and tension and at a reasonable price. A concrete sub is, for a variety of reasons, a little less sensible.
But I'm not sure how this relates to purrgil at all. We can see that a large pressure chamber needs pretty thick walls of a strong material like concrete. While we don't know atmospheric pressure on Lothal it's pretty reasonable to assume it's around 1 atmosphere. So comparing it to this chamber on Earth seems relevant.
If we saw purrgil dive underwater, that would suggest they are even stronger. But we don't; I'm honestly not sure where submarines come into this at all?