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