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