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