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