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