What action constitutes a violation of OSHA standards in chemical safety?

Pouring water into acid is a significant violation of safety protocols related to chemical handling and can lead to dangerous reactions. When water is added to concentrated acid, it can cause an exothermic reaction that releases heat rapidly, leading to splattering or boiling. This method of dilution can result in severe burns or explosions, making it critical to adhere to proper procedures, which specify adding acid to water instead.

The actions associated with the other choices, while serious and also represent safety violations or poor practices, do not necessarily reflect the immediate and acute danger related to chemical reactions that is exemplified in the case of improper mixing of water and acid. Each of those situations—using unmarked containers, not wearing personal protective equipment, and failing to label hazardous materials—also poses risks, but they do not have the same level of immediate chemical reaction hazards as improperly mixing water and acid.