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