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.
Accept G-Man’s offer of employment.
View the *other* secret ending.
Take out all three Healing Crystals in Nihilanth’s Chamber at the same time.
Complete Interloper without taking any laser damage.
Don't kill any Vortigaunts in the Borderworld.
Conduct all of the questionable research experiments.
Kill 10 enemies with a reprogrammed Sentry.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Decline G-Man’s offer of employment.
Carry the Hidden Hat to Endgame.
Defeat Nihilanth in under 4 minutes.
Kill all Protozoans in the Borderworld.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
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 Cyanogen to kill Gonarch.
Don't use the Cyanogen and let the Gonarch live.
Find each member of the missing research teams.
Get whacked into oblivion in the ledge fight.
Kill an Icthyosaur with either the Tau or Gluon.
Use the welcome mat.
Skip the opening Xen island with a secret jump.
Send the Hidden Hat to Xen.
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.
Kill 20 enemies with the Hivehand.
Cook a Grenade for too long.
Kill 5 enemies with one grenade.
Kill 10 enemies with Snarks.
Overcharge it anyway.
Get killed by your own Snarks.
Kill an Assassin with the .357 Magnum.
Kill 10 Enemies with Tripmines.
Headshot 20 enemies with the .357 magnum.
Kill a Barnacle with a Satchel.
Kill 10 Airborne Headcrabs using the Shotgun.
Help the Barnacle and Headcrab find true love.
Kill a Marine with their own grenade.
Get overtaken by a Headcrab's ample anterior.
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 a Headcrab using fire.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
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.