What type of signs are acceptable for laboratories that store or use severely hazardous materials?

Lettered or pictured signs are acceptable for laboratories that store or use severely hazardous materials because they effectively communicate the specific risks associated with those materials. These signs can include clear letters, symbols, or images that provide immediate recognition and understanding of the hazards present, thereby enhancing safety within the laboratory environment. The use of recognizable visuals or written warnings helps ensure that all personnel, regardless of language proficiency or familiarity with chemical names, can quickly identify potential dangers and take appropriate precautions.

In contrast to the other options, which may not provide the necessary clarity or immediacy, lettered or pictured signs are specifically designed to convey critical safety information in an easily understandable manner, making them a standard requirement in hazardous environments.