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