Gas Masks should be a Tier 2 item, Tier 3 at the latest, not Tier 5. There's no good reason Ficsyt wouldn't provide their planet side employees with equipment to protect them from local hazards like poison gas. Gas masks should unlock as soon as coal unlocks, which can be used to make charcoal, which itself can be converted to activated charcoal and is a key material in real life gas masks that protect against toxins and poisons in the air, such as from chemical attacks.