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