Rudimentary carbon dioxide scrubbers[0], with a reserve oxygen supply.<p>0:<a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Soda_lime#Undersea_use" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Soda_lime#Undersea_use</a>