Complex sentence: Once the inflatable survival suit has been put on and zipped shut, the wearer puts firing handles on compressed carbon dioxide cartridges, which punctures the cartridges and rapidly inflates the suit into a highly buoyant, rigid shape that also offers very high thermal retention properties.
Split into simpler sentences: Once the inflatable survival suit has been put on and zipped shut, the wearer activates firing handles on compressed carbon dioxide cartridges, which punctures the cartridges and rapidly inflates the suit. This results in a into a highly buoyant, rigid shape that also offers very high thermal retention properties.