You can unlock this achievement in Casual but make sure you don't have any modifiers.

Once you turn on the power, head to the Generators and activate the console to Enable Ventilation Systems. Then Survive the lockdown.

Next repair the 4 ventilation Units located in houses which are emitting nova gas.

Once that is complete you will unlock the achievement if you do it by round 5.



Achievement is worth 15 Gamerscore.