How do I get the "Ethically Questionable" achievement in Black Mesa?

I've almost completed Chapter 3 "Unforeseen Consequences" and haven't seen anything which looks like it could be related to this achievement. What do I need to do in order to unlock this achievement?

The Ethically Questionable achievement comprises of the following actions and occur during the 'Questionably Ethical' chapter;

• Killing an alien grunt with poisonous gas
• Using the tesla discharge on the bullsquid
• Using poisonous gas on the headcrabs in their habitat
• Shooting the headcrabs with a laser
• Firing the snark cannon until it breaks

As mentioned by PWhite these are all segmented off in their own separate rooms where you're generally presented with a button to press to activate lasers.

I am unsure about in BMS, but in the original Half-Life, some room contained what could be considered "questionable experiments." They occur later in the game, and take the form of rooms where there are (usually caged) aliens and a button. Pressing the button will kill the aliens. This may be what you are searching for.