What is the purpose of the lab in The Divide?

It doesn't look like it explains the lab

After time passes the shelter's door is broken open and the shelter is invaded by armed soldiers in biohazard suits; the men's speech is unintelligible and their allegiance remains ambiguous.

After exploring the lab, Josh runs back into the shelter after being identified at which point the door is welded shut. This leads me to believe that the lab was setup there for some other purpose other than the occupants of the shelter and may have originally burst in because they intended to occupy it for themselves but after finding resistance they retreated, but not without first taking a test subject.

Josh's outfit allows him to explore the lab where he discovers several unconscious children—including Wendi—in stasis units; their hair shaved off and their eyes bandaged.

Being in a post-apocalyptic setting, it's possible that the lab was setup to prevent contamination and the children may have been shaved to get rid of radioactive contamination and placed in the stasis tanks to be protected or cleansed.

Or, the lab was setup to perform experiments on people and that's why suits broke into the shelter to begin with. Who knows. But with the reaction to Josh when they see he isn't supposed to be there, they were either there to do harm or he was just mad about his buddies getting attacked in the previous encounter with the shelter inhabitants.

If you examine the final scene after Eva escapes, she finds the city in ruin. So it doesn't seem as if the lab was actually there for malicious purposes or containment (like in Quarantine).

However, the real reason is not revealed to us and is just there to add an element of terror and explain why they just can't walk out the door. It has even less significance when you consider that once the door was welded shut, the lab and suits were forgotten.

There is a lot of ambiguity and confusion as to the purpose of the lab which suggests it wasn't meant to be explained as part of the story line.