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