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