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