Complex sentence: Since the ship carried chemical suits, instead of radiation suits, they were certain to be lethally contaminated, but the repair team was not aware of that, believing the suits they wore would protect them from contamination.
Split into simpler sentences: Since the ship carried chemical suits, instead of radiation suits, they were certain to be lethally contaminated. But the repair team was not aware of that, believing the suits they wore would protect them from contamination.