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.
Accept G-Man’s offer of employment.
Decline G-Man’s offer of employment.
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.
Find the snack supply canister.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Get whacked into oblivion in the ledge fight.
Use the welcome mat.
Skip the opening Xen island with a secret jump.
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.
Kill 10 enemies with a reprogrammed Sentry.
Kill an Icthyosaur with either the Tau or Gluon.
Kill 10 enemies with Snarks.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 10 Enemies with Tripmines.
Kill 20 enemies with the Hivehand.
Get killed by your own Snarks.
Overcharge it anyway.
Conduct all of the questionable research experiments.
Kill an Assassin with the .357 Magnum.
Headshot 20 enemies with the .357 magnum.
Kill 5 enemies with one grenade.
Kill a Barnacle with a Satchel.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill a Marine with their own grenade.
Kill a Headcrab using fire.
Cook a Grenade for too long.
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.
Ruin the microwave casserole.
Pass the toilet paper to the scientist in need.
Use the alternate path in Office Complex.
Send the Hidden Hat to Xen.
Help the Barnacle and Headcrab find true love.
Kill all Protozoans in the Borderworld.
Carry the Hidden Hat to Endgame.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Deliver the finishing blow to Gonarch with your Crowbar.
Find each member of the missing research teams.
Use Cyanogen to kill Gonarch.
Don't use the Cyanogen and let the Gonarch live.
Complete Interloper without taking any laser damage.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
View the *other* secret ending.