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