Other mistake: When the gate is activated (after O'Neill tells Woosley about the order to nuke the city), a member of the Atlantis team is on the bottom right, even though the Replicators have control of the city and no one from the Atlantis team is in the control room. This is because it's a reused establishing shot used throughout the series, including the series finale when the gate is activated (after Harriman says the Earth Stargate is offline).
Other mistake: McKay and Jackson enters a room and runs into 2 armored figures, Jackson eventually reveals that they are empty suits, however in every shot shot from behind the suits, the suits are constantly moving, as if they are hanging on strings.
Other mistake: In Shepard's apartment, there is a fresh pineapple and other fruit in his kitchen. This despite him having been in Atlantis for several months. This later turns out to be an artificial reality, but that should've been a big hint.
Answer: Those are actually suits that protect from hazardous chemicals. They are cheaper for the prop department and look nearly the same as biohazard suits. A real biohazard suit would indeed have a helmet that seals to the neck.
Grumpy Scot