The airborne concentrations of substances (such as hydrogen sulfide) under which nearly all workers may be repeatedly exposed without adverse effects are called __________.

Correct Answer: Option C — threshold limit values

Threshold Limit Values (TLVs) represent the airborne concentration of substances to which nearly all workers can be exposed day after day without adverse health effects. These values are established by the ACGIH and are critical for maintaining a safe working environment in hazardous maritime engineering spaces.