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.
Die in the AMS Beam before starting the experiment.
Accept G-Man’s offer of employment.
Decline 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.
Defeat Nihilanth in under 4 minutes.
Carry the Hidden Hat to Endgame.
Complete Interloper without taking any laser damage.
Don't kill any Vortigaunts in the Borderworld.
Find the snack supply canister.
Find each member of the missing research teams.
Use the welcome mat.
Escape the Gargantua’s Lair without taking any damage from Gargantuas.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Don't use the Cyanogen and let the Gonarch live.
Use Cyanogen to kill Gonarch.
Kill all Protozoans in the Borderworld.
Deliver the finishing blow to Gonarch with your Crowbar.
Get whacked into oblivion in the ledge fight.
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.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Kill 10 Enemies with Tripmines.
Cook a Grenade for too long.
Use an entire clip of Gluon ammo in one continuous shot.
Kill 20 enemies with the Hivehand.
Send the Hidden Hat to Xen.
Drown in Lambda Core's coolant.
Conduct all of the questionable research experiments.
Kill 10 enemies with Snarks.
Kill an Icthyosaur with either the Tau or Gluon.
Kill 10 enemies with a reprogrammed Sentry.
Overcharge it anyway.
Get killed by your own Snarks.
Kill an Assassin with the .357 Magnum.
Kill 5 enemies with one grenade.
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.
Use the alternate path in Office Complex.
Headshot 20 enemies with the .357 magnum.
Perform surgical caffeine extraction from 20 machines.
Get overtaken by a Headcrab's ample anterior.
Kill a Headcrab using fire.
Interfere with the alarm and laptop in Anomalous Materials.
Refuse to insert the specimen into the Anti-Mass Spectrometer.
Ruin the microwave casserole.
Pass the toilet paper to the scientist in need.