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