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