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