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.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Get whacked into oblivion in the ledge fight.
Skip the opening Xen island with a secret jump.
Kill a Barnacle with a Satchel.
Use the alternate path in Office Complex.
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.
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.
Deliver the finishing blow to Gonarch with your Crowbar.
Use the welcome mat.
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.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 20 enemies with the Hivehand.
Kill 10 enemies with Snarks.
Kill an Icthyosaur with either the Tau or Gluon.
Conduct all of the questionable research experiments.
Overcharge it anyway.
Get killed by your own Snarks.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Cook a Grenade for too long.
Kill 10 enemies with a reprogrammed Sentry.
Kill 10 Airborne Headcrabs using the Shotgun.
Help the Barnacle and Headcrab find true love.
Kill a Marine with their own grenade.
Kill 5 enemies with one grenade.
Kill a Headcrab using fire.
Get overtaken by a Headcrab's ample anterior.
Headshot 20 enemies with the .357 magnum.
Perform surgical caffeine extraction from 20 machines.
Pass the toilet paper to the scientist in need.
Ruin the microwave casserole.
Send the Hidden Hat to Xen.
Kill all Protozoans in the Borderworld.
Carry the Hidden Hat to Endgame.
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.