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