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