From Black Mesa: Wiki

Overview

The Hazard Course was originally featured as an optional training level in Half-Life. It is a tutorial for those who are new to the game.

Gameplay

The player is guided through the course by a holographic version of Gina Cross (for HEV Suit users) and Miller (for Black Mesa Security Personnel). The course covers the basic functions of the Hazardous Environment Suit; simple movements such as jumping, crouching and swimming; weapons training; and cooperating with other Black Mesa Personnel.

Black Mesa's Cut

In Raminator's own words, the Hazard Course "is a waste of development time that would be better spent on polishing the singleplayer component and getting the multiplayer component to a releasable beta status (...). It has nothing to do with the storyline, and I think we can agree that games these days have moved beyond the need for a separate training section". [1]

So, while the Hazard Course was originally slated to be a part of the release, it was dropped in favor of better developing other parts of the mod. Should the player require assistance, however, Black Mesa will give instructions in HUD hints throughout Anomalous Materials and Unforeseen Consequences, similar to the ones in Half-Life 2 and the Episodes.

Trivia

• Victoria Teunissen completed the voice recordings for Black Mesa's Gina Cross before the Hazard Course was cut. [2]
• After its cancellation, the Black Mesa community began developing their own version of the Hazard Course in Source. For more details, check here.