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