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