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