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.
Carry the Hidden Hat to Endgame.
Accept G-Man’s offer of employment.
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.
Deliver the finishing blow to Gonarch with your Crowbar.
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.
Wait too long to jump into the Lambda Teleporter.
Kill 10 Enemies with Tripmines.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Die in the AMS Beam before starting the experiment.
Cook a Grenade for too long.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Skip the opening Xen island with a secret jump.
Decline G-Man’s offer of employment.
Send the Hidden Hat to Xen.
Help the Barnacle and Headcrab find true love.
Get killed by your own Snarks.
Kill 10 enemies with Snarks.
Kill a Headcrab using fire.
Kill 10 enemies with a reprogrammed Sentry.
Use the alternate path in Office Complex.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Kill 10 Airborne Headcrabs using the Shotgun.
Drown in Lambda Core's coolant.
Use an entire clip of Gluon ammo in one continuous shot.
Headshot 20 enemies with the .357 magnum.
Kill 20 enemies with the Hivehand.
Kill 5 enemies with one grenade.
Get overtaken by a Headcrab's ample anterior.
Kill an Icthyosaur with either the Tau or Gluon.
Kill a Marine with their own grenade.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Kill an Assassin with the .357 Magnum.
Interfere with the alarm and laptop in Anomalous Materials.
Perform surgical caffeine extraction from 20 machines.
Kill a Barnacle with a Satchel.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.