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.
Complete Interloper without taking any laser damage.
Don't use the Cyanogen and let the Gonarch live.
Use Cyanogen to kill Gonarch.
Find each member of the missing research teams.
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.
Deliver the finishing blow to Gonarch with your Crowbar.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Kill an Icthyosaur with either the Tau or Gluon.
Skip the opening Xen island with a secret jump.
Send the Hidden Hat to Xen.
Drown in Lambda Core's coolant.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 10 enemies with a reprogrammed Sentry.
Kill 20 enemies with the Hivehand.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Kill 10 enemies with Snarks.
Get killed by your own Snarks.
Kill 10 Enemies with Tripmines.
Help the Barnacle and Headcrab find true love.
Kill a Marine with their own grenade.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Use the alternate path in Office Complex.
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.
Perform surgical caffeine extraction from 20 machines.
Interfere with the alarm and laptop in Anomalous Materials.
Decline G-Man’s offer of employment.
Accept G-Man’s offer of employment.
Use an entire clip of Gluon ammo in one continuous shot.
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.
Kill a Headcrab using fire.
Wait too long to jump into the Lambda Teleporter.
Kill an Assassin with the .357 Magnum.
Kill a Barnacle with a Satchel.
Kill 10 Airborne Headcrabs using the Shotgun.
Cook a Grenade for too long.
Headshot 20 enemies with the .357 magnum.
Kill 5 enemies with one grenade.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.