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