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