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 use the Cyanogen and let the Gonarch live.
Find each member of the missing research teams.
Use Cyanogen to kill Gonarch.
Kill all Protozoans in the Borderworld.
Use the welcome mat.
Get whacked into oblivion in the ledge fight.
Decline G-Man’s offer of employment.
Accept G-Man’s offer of employment.
Carry the Hidden Hat to Endgame.
Defeat Nihilanth in under 4 minutes.
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.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Deliver the finishing blow to Gonarch with your Crowbar.
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.
Use an entire clip of Gluon ammo in one continuous shot.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 20 enemies with the Hivehand.
Kill 10 enemies with Snarks.
Kill an Icthyosaur with either the Tau or Gluon.
Get killed by your own Snarks.
Overcharge it anyway.
Conduct all of the questionable research experiments.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Headshot 20 enemies with the .357 magnum.
Kill a Barnacle with a Satchel.
Kill 5 enemies with one grenade.
Help the Barnacle and Headcrab find true love.
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.
Kill 10 Airborne Headcrabs using the Shotgun.
Use the alternate path in Office Complex.
Cook a Grenade for too long.
Kill a Headcrab using fire.
Perform surgical caffeine extraction from 20 machines.
Get overtaken by a Headcrab's ample anterior.
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.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.