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