The airborne concentrations of substances (such as H2S) under which nearly all workers may be repeatedly exposed without adverse effects defines which of the following phrases?

Correct Answer: Option C — threshold limit values

Threshold Limit Values (TLV) are established by industrial hygiene standards to define the airborne concentration of a substance to which nearly all workers can be exposed day after day without adverse health effects. These values are critical for maintaining a safe working environment aboard vessels handling hazardous materials like H2S.