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