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