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