Here is the full list of all 35 Insurgency: Sandstorm achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Kill 3 enemies with a headshot in a row.
Win a match of Checkpoint.
Kill an enemy with the last bullet of your magazine.
Purchase your first item in the Appearance menu.
Capture an objective as the last member of the team alive.
Kill an enemy with a knife.
Get the first kill in a round.
Win a match of Firefight.
Kill an enemy after blinding them with a flashbang
Kill an enemy while they are reloading.
Win a match of Push.
Kill an enemy by shooting through something.
Block an objective from being captured and then clear it.
Kill an enemy without using weapon sights.
Kill an enemy right after performing a speed reload.
Complete the tutorial mission.
Destroy an enemy weapon cache using a remote explosive charge.
Successfully rig and destroy an enemy weapon cache.
Kill an enemy with an enemy's live grenade.
Kill three or more enemies with a single grenade or explosive.
As a Commander, kill an enemy using fire support.
Kill an enemy by bashing in a door.
Destroy an enemy air support vehicle.
Destroy an enemy vehicle with a mine.
Drive a vehicle full of teammates for more than 15 seconds.
Kill an enemy with a vehicle.
Kill an enemy using the mounted weapon on a vehicle.
Kill an enemy driver with the mounted weapon of their vehicle.
Be the Most Valuable Player of a round.
Capture 100 objectives.
Call in fire support ten times as an Observer.
Kill an enemy while blinded by a flashbang
Kill an enemy while vaulting.
Kill an enemy by burning them.
Navigate through chemical gas while wearing a gas mask.