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