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