Dust and smoke particles image - Diffusion mod for Half-Life

You, James Smith (served in SWAT for a decade with no failed ops), on vacation and driving your car to some nice place, to take a break from your usual work routines. Driving on a deserted road somewhere in Utah, the car breaks down. With miles of nothing behind, J. decides to go forward and stumbles upon an abandoned rock/sand processing factory with just one yawning guard sitting there. Pointed by the guard, J. walks behind the factory to find the phone. When he comes back, he only sees two army trucks and the dead guard… J.'s curiosity leads him inside the factory only to find that this place is absolutely not what it seems to be…