Biohazard guards are simply mercenaries wearing protective Hazmat suits. They initially wield M4s but later in the game they will carry P90s. One is also seen wielding a Desert Eagle once in the entire game. These guards are rare and typically found in hazardous environments such as the catacombs where nerve gas was deployed to counter the Trigens but are not particularly a large threat, especially compared to other mercenaries and the Trigens. The only unique trait they have that the other mercs lack is they can travel through areas which are saturated with nerve gas.
- Though Biohazard guards are never seen wielding or using Jackhammers, it is interesting to note that at the start of the level Rebellion, near the first trigen seen in the level, a jackhammer is on the ground. If the player goes to the next room, the corpse of a Biohazard guard is in the room but there are no weapons around him, which mean he could have been wielding the weapon but was killed by the trigens and was either flung or dragged into the next room .
- It is possible that the Jackhammer at the very start of the level Rebellion belonged to one of the 3 dead indoor guard mercenaries found in the room after the Corpse of the Biohazard guard.