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