The S90 Gas Mask is a type of Gas mask used by the UNSC Marine Corps. Gas masks are used by ground forces for protection against chemical or biological weapons. Each S90 Gas mask weighs about 0.3 kilograms (0.66 lb). The gas masks might also be used as part of a survival kit like the ones that John-117 mentioned at the Battle of Sigma Octanus IV.
- This piece of UNSC equipment is not seen in gameplay but is seen labeled on cargo containers in Halo 2 and Halo 3.
- The gas mask that appears on the crate resembles the real life British S10 gas mask.