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