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