The HAZMAT Unit members wear white suits with a light green tinted visor and tall white boots. They have red tanks on their backs. In "Pineapple Invasion," they have visible eyes, while their eyes are not visible in their first two appearances.
The HAZMAT Unit first appears in "Best Frenemies," to remove the toxic material that was sold in the Kelpshake restaurants.
Lastly, the HAZMAT Unit appears in "Jolly Lodgers" when Squidward calls them in order for them to send exterminators to condemn the hotel so he could get out of the situation with the jellyfishing convention, even though there was no danger actually happening.