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