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