A bio-hazard locker was a containment compartment used aboard Enterprise NX-01, for the purpose of storing material that could be hazardous or toxic to the crew. In 2153, upon discovering that trellium-D was toxic to Vulcans, Captain Archer ordered their supply of trellium be stored in a bio-hazard locker so that T'Pol would not be affected by it. (ENT: "Impulse")