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