Here is the full list of all 50 Black Mesa achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Don't kill any Vortigaunts in the Borderworld.
View the *other* secret ending.
Kill all Protozoans in the Borderworld.
Don't use the Cyanogen and let the Gonarch live.
Use Cyanogen to kill Gonarch.
Find each member of the missing research teams.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Carry the Hidden Hat to Endgame.
Deliver the finishing blow to Gonarch with your Crowbar.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Wait too long to jump into the Lambda Teleporter.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 10 Enemies with Tripmines.
Skip the opening Xen island with a secret jump.
Complete Interloper without taking any laser damage.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Find the snack supply canister.
Defeat Nihilanth in under 4 minutes.
Accept G-Man’s offer of employment.
Decline G-Man’s offer of employment.
Cook a Grenade for too long.
Die in the AMS Beam before starting the experiment.
Send the Hidden Hat to Xen.
Kill 5 enemies with one grenade.
Help the Barnacle and Headcrab find true love.
Kill a Headcrab using fire.
Get overtaken by a Headcrab's ample anterior.
Kill 10 enemies with Snarks.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill 10 enemies with a reprogrammed Sentry.
Kill an Icthyosaur with either the Tau or Gluon.
Kill 20 enemies with the Hivehand.
Kill a Barnacle with a Satchel.
Kill a Marine with their own grenade.
Use an entire clip of Gluon ammo in one continuous shot.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Drown in Lambda Core's coolant.
Kill an Assassin with the .357 Magnum.
Conduct all of the questionable research experiments.
Headshot 20 enemies with the .357 magnum.
Use the alternate path in Office Complex.
Perform surgical caffeine extraction from 20 machines.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.
Get killed by your own Snarks.
Overcharge it anyway.