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.
Find each member of the missing research teams.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Use the alternate path in Office Complex.
View the *other* secret ending.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Find the snack supply canister.
Complete Interloper without taking any laser damage.
Kill all Protozoans in the Borderworld.
Carry the Hidden Hat to Endgame.
Send the Hidden Hat to Xen.
Don't kill any Vortigaunts in the Borderworld.
Get whacked into oblivion in the ledge fight.
Deliver the finishing blow to Gonarch with your Crowbar.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Don't use the Cyanogen and let the Gonarch live.
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.
Use Cyanogen to kill Gonarch.
Use the welcome mat.
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.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill an Icthyosaur with either the Tau or Gluon.
Kill 20 enemies with the Hivehand.
Kill 10 enemies with Snarks.
Get killed by your own Snarks.
Overcharge it anyway.
Conduct all of the questionable research experiments.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Headshot 20 enemies with the .357 magnum.
Kill a Barnacle with a Satchel.
Kill a Marine with their own grenade.
Kill 10 enemies with a reprogrammed Sentry.
Kill 10 Airborne Headcrabs using the Shotgun.
Cook a Grenade for too long.
Kill 5 enemies with one grenade.
Help the Barnacle and Headcrab find true love.
Kill a Headcrab using fire.
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.
Perform surgical caffeine extraction from 20 machines.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Interfere with the alarm and laptop in Anomalous Materials.