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