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.
Kill a Headcrab using fire.
Accept G-Man’s offer of employment.
Decline G-Man’s offer of employment.
Don't kill any Vortigaunts in the Borderworld.
Complete Interloper without taking any laser damage.
Find the snack supply canister.
Kill a Controller without killing any of its mind-controlled Vortigaunt slaves.
Use an entire clip of Gluon ammo in one continuous shot.
Escape the Hangar in Surface Tension without alerting the Soldiers.
Kill 5 enemies with one grenade.
Kill 10 Airborne Headcrabs using the Shotgun.
Kill 20 enemies with the Hivehand.
Kill an Icthyosaur with either the Tau or Gluon.
Kill an Assassin with the .357 Magnum.
Headshot 20 enemies with the .357 magnum.
Kill a Barnacle with a Satchel.
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.
Interfere with the alarm and laptop in Anomalous Materials.
Perform surgical caffeine extraction from 20 machines.
Kill 10 enemies with a reprogrammed Sentry.
Conduct all of the questionable research experiments.
Kill 10 enemies with Snarks.
Drown in Lambda Core's coolant.
Kill a Marine with their own grenade.
Get overtaken by a Headcrab's ample anterior.
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.
Kill 10 Enemies with Tripmines.
Wait too long to jump into the Lambda Teleporter.
Assemble all the possible Scientists and Guards at the end of Office Complex.
Die in the AMS Beam before starting the experiment.
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.
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.
Cook a Grenade for too long.