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